CbC/CbC_llvm: docs/AliasAnalysis.rst annotate

annotate docs/AliasAnalysis.rst @ 18:5abb684876c4

report error when code segment's tail call flag was changed false

author	Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
date	Sun, 06 Oct 2013 00:17:31 +0900
parents	9ad51c7bc036
children	54457678186b

rev	line source
3 9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	1 ==================================
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	2 LLVM Alias Analysis Infrastructure
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	3 ==================================
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	4
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	5 .. contents::
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	6 :local:
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	7
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	8 Introduction
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	9 ============
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	10
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	11 Alias Analysis (aka Pointer Analysis) is a class of techniques which attempt to
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	12 determine whether or not two pointers ever can point to the same object in
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	13 memory. There are many different algorithms for alias analysis and many
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	14 different ways of classifying them: flow-sensitive vs. flow-insensitive,
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	15 context-sensitive vs. context-insensitive, field-sensitive
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	16 vs. field-insensitive, unification-based vs. subset-based, etc. Traditionally,
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	17 alias analyses respond to a query with a `Must, May, or No`_ alias response,
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	18 indicating that two pointers always point to the same object, might point to the
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	19 same object, or are known to never point to the same object.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	20
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	21 The LLVM `AliasAnalysis
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	22 <http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html>`__ class is the
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	23 primary interface used by clients and implementations of alias analyses in the
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	24 LLVM system. This class is the common interface between clients of alias
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	25 analysis information and the implementations providing it, and is designed to
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	26 support a wide range of implementations and clients (but currently all clients
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	27 are assumed to be flow-insensitive). In addition to simple alias analysis
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	28 information, this class exposes Mod/Ref information from those implementations
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	29 which can provide it, allowing for powerful analyses and transformations to work
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	30 well together.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	31
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	32 This document contains information necessary to successfully implement this
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	33 interface, use it, and to test both sides. It also explains some of the finer
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	34 points about what exactly results mean. If you feel that something is unclear
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	35 or should be added, please `let me know <mailto:sabre@nondot.org>`_.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	36
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	37 ``AliasAnalysis`` Class Overview
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	38 ================================
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	39
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	40 The `AliasAnalysis <http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html>`__
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	41 class defines the interface that the various alias analysis implementations
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	42 should support. This class exports two important enums: ``AliasResult`` and
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	43 ``ModRefResult`` which represent the result of an alias query or a mod/ref
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	44 query, respectively.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	45
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	46 The ``AliasAnalysis`` interface exposes information about memory, represented in
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	47 several different ways. In particular, memory objects are represented as a
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	48 starting address and size, and function calls are represented as the actual
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	49 ``call`` or ``invoke`` instructions that performs the call. The
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	50 ``AliasAnalysis`` interface also exposes some helper methods which allow you to
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	51 get mod/ref information for arbitrary instructions.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	52
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	53 All ``AliasAnalysis`` interfaces require that in queries involving multiple
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	54 values, values which are not `constants <LangRef.html#constants>`_ are all
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	55 defined within the same function.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	56
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	57 Representation of Pointers
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	58 --------------------------
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	59
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	60 Most importantly, the ``AliasAnalysis`` class provides several methods which are
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	61 used to query whether or not two memory objects alias, whether function calls
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	62 can modify or read a memory object, etc. For all of these queries, memory
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	63 objects are represented as a pair of their starting address (a symbolic LLVM
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	64 ``Value*``) and a static size.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	65
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	66 Representing memory objects as a starting address and a size is critically
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	67 important for correct Alias Analyses. For example, consider this (silly, but
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	68 possible) C code:
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	69
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	70 .. code-block:: c++
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	71
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	72 int i;
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	73 char C[2];
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	74 char A[10];
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	75 /* ... */
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	76 for (i = 0; i != 10; ++i) {
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	77 C[0] = A[i]; /* One byte store */
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	78 C[1] = A[9-i]; /* One byte store */
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	79 }
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	80
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	81 In this case, the ``basicaa`` pass will disambiguate the stores to ``C[0]`` and
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	82 ``C[1]`` because they are accesses to two distinct locations one byte apart, and
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	83 the accesses are each one byte. In this case, the Loop Invariant Code Motion
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	84 (LICM) pass can use store motion to remove the stores from the loop. In
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	85 constrast, the following code:
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	86
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	87 .. code-block:: c++
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	88
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	89 int i;
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	90 char C[2];
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	91 char A[10];
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	92 /* ... */
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	93 for (i = 0; i != 10; ++i) {
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	94 ((short)C)[0] = A[i]; / Two byte store! */
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	95 C[1] = A[9-i]; /* One byte store */
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	96 }
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	97
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	98 In this case, the two stores to C do alias each other, because the access to the
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	99 ``&C[0]`` element is a two byte access. If size information wasn't available in
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	100 the query, even the first case would have to conservatively assume that the
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	101 accesses alias.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	102
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	103 .. _alias:
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	104
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	105 The ``alias`` method
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	106 --------------------
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	107
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	108 The ``alias`` method is the primary interface used to determine whether or not
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	109 two memory objects alias each other. It takes two memory objects as input and
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	110 returns MustAlias, PartialAlias, MayAlias, or NoAlias as appropriate.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	111
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	112 Like all ``AliasAnalysis`` interfaces, the ``alias`` method requires that either
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	113 the two pointer values be defined within the same function, or at least one of
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	114 the values is a `constant <LangRef.html#constants>`_.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	115
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	116 .. _Must, May, or No:
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	117
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	118 Must, May, and No Alias Responses
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	119 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	120
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	121 The ``NoAlias`` response may be used when there is never an immediate dependence
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	122 between any memory reference based on one pointer and any memory reference
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	123 based the other. The most obvious example is when the two pointers point to
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	124 non-overlapping memory ranges. Another is when the two pointers are only ever
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	125 used for reading memory. Another is when the memory is freed and reallocated
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	126 between accesses through one pointer and accesses through the other --- in this
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	127 case, there is a dependence, but it's mediated by the free and reallocation.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	128
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	129 As an exception to this is with the `noalias <LangRef.html#noalias>`_ keyword;
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	130 the "irrelevant" dependencies are ignored.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	131
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	132 The ``MayAlias`` response is used whenever the two pointers might refer to the
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	133 same object.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	134
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	135 The ``PartialAlias`` response is used when the two memory objects are known to
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	136 be overlapping in some way, but do not start at the same address.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	137
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	138 The ``MustAlias`` response may only be returned if the two memory objects are
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	139 guaranteed to always start at exactly the same location. A ``MustAlias``
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	140 response implies that the pointers compare equal.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	141
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	142 The ``getModRefInfo`` methods
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	143 -----------------------------
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	144
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	145 The ``getModRefInfo`` methods return information about whether the execution of
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	146 an instruction can read or modify a memory location. Mod/Ref information is
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	147 always conservative: if an instruction might read or write a location,
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	148 ``ModRef`` is returned.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	149
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	150 The ``AliasAnalysis`` class also provides a ``getModRefInfo`` method for testing
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	151 dependencies between function calls. This method takes two call sites (``CS1``
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	152 & ``CS2``), returns ``NoModRef`` if neither call writes to memory read or
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	153 written by the other, ``Ref`` if ``CS1`` reads memory written by ``CS2``,
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	154 ``Mod`` if ``CS1`` writes to memory read or written by ``CS2``, or ``ModRef`` if
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	155 ``CS1`` might read or write memory written to by ``CS2``. Note that this
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	156 relation is not commutative.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	157
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	158 Other useful ``AliasAnalysis`` methods
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	159 --------------------------------------
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	160
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	161 Several other tidbits of information are often collected by various alias
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	162 analysis implementations and can be put to good use by various clients.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	163
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	164 The ``pointsToConstantMemory`` method
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	165 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	166
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	167 The ``pointsToConstantMemory`` method returns true if and only if the analysis
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	168 can prove that the pointer only points to unchanging memory locations
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	169 (functions, constant global variables, and the null pointer). This information
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	170 can be used to refine mod/ref information: it is impossible for an unchanging
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	171 memory location to be modified.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	172
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	173 .. _never access memory or only read memory:
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	174
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	175 The ``doesNotAccessMemory`` and ``onlyReadsMemory`` methods
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	176 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	177
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	178 These methods are used to provide very simple mod/ref information for function
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	179 calls. The ``doesNotAccessMemory`` method returns true for a function if the
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	180 analysis can prove that the function never reads or writes to memory, or if the
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	181 function only reads from constant memory. Functions with this property are
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	182 side-effect free and only depend on their input arguments, allowing them to be
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	183 eliminated if they form common subexpressions or be hoisted out of loops. Many
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	184 common functions behave this way (e.g., ``sin`` and ``cos``) but many others do
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	185 not (e.g., ``acos``, which modifies the ``errno`` variable).
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	186
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	187 The ``onlyReadsMemory`` method returns true for a function if analysis can prove
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	188 that (at most) the function only reads from non-volatile memory. Functions with
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	189 this property are side-effect free, only depending on their input arguments and
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	190 the state of memory when they are called. This property allows calls to these
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	191 functions to be eliminated and moved around, as long as there is no store
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	192 instruction that changes the contents of memory. Note that all functions that
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	193 satisfy the ``doesNotAccessMemory`` method also satisfies ``onlyReadsMemory``.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	194
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	195 Writing a new ``AliasAnalysis`` Implementation
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	196 ==============================================
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	197
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	198 Writing a new alias analysis implementation for LLVM is quite straight-forward.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	199 There are already several implementations that you can use for examples, and the
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	200 following information should help fill in any details. For a examples, take a
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	201 look at the `various alias analysis implementations`_ included with LLVM.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	202
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	203 Different Pass styles
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	204 ---------------------
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	205
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	206 The first step to determining what type of :doc:`LLVM pass <WritingAnLLVMPass>`
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	207 you need to use for your Alias Analysis. As is the case with most other
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	208 analyses and transformations, the answer should be fairly obvious from what type
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	209 of problem you are trying to solve:
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	210
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	211 #. If you require interprocedural analysis, it should be a ``Pass``.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	212 #. If you are a function-local analysis, subclass ``FunctionPass``.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	213 #. If you don't need to look at the program at all, subclass ``ImmutablePass``.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	214
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	215 In addition to the pass that you subclass, you should also inherit from the
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	216 ``AliasAnalysis`` interface, of course, and use the ``RegisterAnalysisGroup``
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	217 template to register as an implementation of ``AliasAnalysis``.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	218
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	219 Required initialization calls
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	220 -----------------------------
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	221
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	222 Your subclass of ``AliasAnalysis`` is required to invoke two methods on the
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	223 ``AliasAnalysis`` base class: ``getAnalysisUsage`` and
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	224 ``InitializeAliasAnalysis``. In particular, your implementation of
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	225 ``getAnalysisUsage`` should explicitly call into the
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	226 ``AliasAnalysis::getAnalysisUsage`` method in addition to doing any declaring
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	227 any pass dependencies your pass has. Thus you should have something like this:
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	228
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	229 .. code-block:: c++
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	230
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	231 void getAnalysisUsage(AnalysisUsage &AU) const {
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	232 AliasAnalysis::getAnalysisUsage(AU);
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	233 // declare your dependencies here.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	234 }
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	235
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	236 Additionally, your must invoke the ``InitializeAliasAnalysis`` method from your
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	237 analysis run method (``run`` for a ``Pass``, ``runOnFunction`` for a
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	238 ``FunctionPass``, or ``InitializePass`` for an ``ImmutablePass``). For example
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	239 (as part of a ``Pass``):
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	240
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	241 .. code-block:: c++
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	242
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	243 bool run(Module &M) {
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	244 InitializeAliasAnalysis(this);
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	245 // Perform analysis here...
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	246 return false;
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	247 }
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	248
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	249 Interfaces which may be specified
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	250 ---------------------------------
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	251
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	252 All of the `AliasAnalysis
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	253 <http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html>`__ virtual methods
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	254 default to providing :ref:`chaining <aliasanalysis-chaining>` to another alias
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	255 analysis implementation, which ends up returning conservatively correct
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	256 information (returning "May" Alias and "Mod/Ref" for alias and mod/ref queries
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	257 respectively). Depending on the capabilities of the analysis you are
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	258 implementing, you just override the interfaces you can improve.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	259
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	260 .. _aliasanalysis-chaining:
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	261
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	262 ``AliasAnalysis`` chaining behavior
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	263 -----------------------------------
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	264
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	265 With only one special exception (the :ref:`-no-aa <aliasanalysis-no-aa>` pass)
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	266 every alias analysis pass chains to another alias analysis implementation (for
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	267 example, the user can specify "``-basicaa -ds-aa -licm``" to get the maximum
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	268 benefit from both alias analyses). The alias analysis class automatically
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	269 takes care of most of this for methods that you don't override. For methods
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	270 that you do override, in code paths that return a conservative MayAlias or
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	271 Mod/Ref result, simply return whatever the superclass computes. For example:
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	272
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	273 .. code-block:: c++
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	274
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	275 AliasAnalysis::AliasResult alias(const Value *V1, unsigned V1Size,
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	276 const Value *V2, unsigned V2Size) {
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	277 if (...)
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	278 return NoAlias;
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	279 ...
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	280
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	281 // Couldn't determine a must or no-alias result.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	282 return AliasAnalysis::alias(V1, V1Size, V2, V2Size);
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	283 }
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	284
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	285 In addition to analysis queries, you must make sure to unconditionally pass LLVM
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	286 `update notification`_ methods to the superclass as well if you override them,
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	287 which allows all alias analyses in a change to be updated.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	288
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	289 .. _update notification:
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	290
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	291 Updating analysis results for transformations
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	292 ---------------------------------------------
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	293
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	294 Alias analysis information is initially computed for a static snapshot of the
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	295 program, but clients will use this information to make transformations to the
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	296 code. All but the most trivial forms of alias analysis will need to have their
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	297 analysis results updated to reflect the changes made by these transformations.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	298
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	299 The ``AliasAnalysis`` interface exposes four methods which are used to
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	300 communicate program changes from the clients to the analysis implementations.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	301 Various alias analysis implementations should use these methods to ensure that
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	302 their internal data structures are kept up-to-date as the program changes (for
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	303 example, when an instruction is deleted), and clients of alias analysis must be
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	304 sure to call these interfaces appropriately.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	305
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	306 The ``deleteValue`` method
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	307 ^^^^^^^^^^^^^^^^^^^^^^^^^^
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	308
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	309 The ``deleteValue`` method is called by transformations when they remove an
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	310 instruction or any other value from the program (including values that do not
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	311 use pointers). Typically alias analyses keep data structures that have entries
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	312 for each value in the program. When this method is called, they should remove
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	313 any entries for the specified value, if they exist.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	314
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	315 The ``copyValue`` method
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	316 ^^^^^^^^^^^^^^^^^^^^^^^^
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	317
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	318 The ``copyValue`` method is used when a new value is introduced into the
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	319 program. There is no way to introduce a value into the program that did not
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	320 exist before (this doesn't make sense for a safe compiler transformation), so
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	321 this is the only way to introduce a new value. This method indicates that the
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	322 new value has exactly the same properties as the value being copied.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	323
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	324 The ``replaceWithNewValue`` method
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	325 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	326
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	327 This method is a simple helper method that is provided to make clients easier to
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	328 use. It is implemented by copying the old analysis information to the new
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	329 value, then deleting the old value. This method cannot be overridden by alias
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	330 analysis implementations.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	331
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	332 The ``addEscapingUse`` method
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	333 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	334
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	335 The ``addEscapingUse`` method is used when the uses of a pointer value have
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	336 changed in ways that may invalidate precomputed analysis information.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	337 Implementations may either use this callback to provide conservative responses
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	338 for points whose uses have change since analysis time, or may recompute some or
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	339 all of their internal state to continue providing accurate responses.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	340
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	341 In general, any new use of a pointer value is considered an escaping use, and
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	342 must be reported through this callback, except for the uses below:
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	343
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	344 * A ``bitcast`` or ``getelementptr`` of the pointer
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	345 * A ``store`` through the pointer (but not a ``store`` of the pointer)
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	346 * A ``load`` through the pointer
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	347
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	348 Efficiency Issues
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	349 -----------------
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	350
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	351 From the LLVM perspective, the only thing you need to do to provide an efficient
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	352 alias analysis is to make sure that alias analysis queries are serviced
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	353 quickly. The actual calculation of the alias analysis results (the "run"
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	354 method) is only performed once, but many (perhaps duplicate) queries may be
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	355 performed. Because of this, try to move as much computation to the run method
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	356 as possible (within reason).
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	357
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	358 Limitations
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	359 -----------
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	360
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	361 The AliasAnalysis infrastructure has several limitations which make writing a
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	362 new ``AliasAnalysis`` implementation difficult.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	363
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	364 There is no way to override the default alias analysis. It would be very useful
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	365 to be able to do something like "``opt -my-aa -O2``" and have it use ``-my-aa``
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	366 for all passes which need AliasAnalysis, but there is currently no support for
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	367 that, short of changing the source code and recompiling. Similarly, there is
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	368 also no way of setting a chain of analyses as the default.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	369
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	370 There is no way for transform passes to declare that they preserve
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	371 ``AliasAnalysis`` implementations. The ``AliasAnalysis`` interface includes
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	372 ``deleteValue`` and ``copyValue`` methods which are intended to allow a pass to
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	373 keep an AliasAnalysis consistent, however there's no way for a pass to declare
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	374 in its ``getAnalysisUsage`` that it does so. Some passes attempt to use
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	375 ``AU.addPreserved<AliasAnalysis>``, however this doesn't actually have any
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	376 effect.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	377
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	378 ``AliasAnalysisCounter`` (``-count-aa``) and ``AliasDebugger`` (``-debug-aa``)
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	379 are implemented as ``ModulePass`` classes, so if your alias analysis uses
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	380 ``FunctionPass``, it won't be able to use these utilities. If you try to use
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	381 them, the pass manager will silently route alias analysis queries directly to
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	382 ``BasicAliasAnalysis`` instead.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	383
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	384 Similarly, the ``opt -p`` option introduces ``ModulePass`` passes between each
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	385 pass, which prevents the use of ``FunctionPass`` alias analysis passes.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	386
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	387 The ``AliasAnalysis`` API does have functions for notifying implementations when
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	388 values are deleted or copied, however these aren't sufficient. There are many
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	389 other ways that LLVM IR can be modified which could be relevant to
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	390 ``AliasAnalysis`` implementations which can not be expressed.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	391
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	392 The ``AliasAnalysisDebugger`` utility seems to suggest that ``AliasAnalysis``
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	393 implementations can expect that they will be informed of any relevant ``Value``
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	394 before it appears in an alias query. However, popular clients such as ``GVN``
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	395 don't support this, and are known to trigger errors when run with the
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	396 ``AliasAnalysisDebugger``.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	397
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	398 Due to several of the above limitations, the most obvious use for the
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	399 ``AliasAnalysisCounter`` utility, collecting stats on all alias queries in a
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	400 compilation, doesn't work, even if the ``AliasAnalysis`` implementations don't
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	401 use ``FunctionPass``. There's no way to set a default, much less a default
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	402 sequence, and there's no way to preserve it.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	403
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	404 The ``AliasSetTracker`` class (which is used by ``LICM``) makes a
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	405 non-deterministic number of alias queries. This can cause stats collected by
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	406 ``AliasAnalysisCounter`` to have fluctuations among identical runs, for
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	407 example. Another consequence is that debugging techniques involving pausing
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	408 execution after a predetermined number of queries can be unreliable.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	409
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	410 Many alias queries can be reformulated in terms of other alias queries. When
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	411 multiple ``AliasAnalysis`` queries are chained together, it would make sense to
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	412 start those queries from the beginning of the chain, with care taken to avoid
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	413 infinite looping, however currently an implementation which wants to do this can
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	414 only start such queries from itself.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	415
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	416 Using alias analysis results
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	417 ============================
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	418
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	419 There are several different ways to use alias analysis results. In order of
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	420 preference, these are:
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	421
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	422 Using the ``MemoryDependenceAnalysis`` Pass
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	423 -------------------------------------------
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	424
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	425 The ``memdep`` pass uses alias analysis to provide high-level dependence
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	426 information about memory-using instructions. This will tell you which store
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	427 feeds into a load, for example. It uses caching and other techniques to be
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	428 efficient, and is used by Dead Store Elimination, GVN, and memcpy optimizations.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	429
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	430 .. _AliasSetTracker:
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	431
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	432 Using the ``AliasSetTracker`` class
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	433 -----------------------------------
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	434
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	435 Many transformations need information about alias sets that are active in
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	436 some scope, rather than information about pairwise aliasing. The
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	437 `AliasSetTracker <http://llvm.org/doxygen/classllvm_1_1AliasSetTracker.html>`__
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	438 class is used to efficiently build these Alias Sets from the pairwise alias
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	439 analysis information provided by the ``AliasAnalysis`` interface.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	440
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	441 First you initialize the AliasSetTracker by using the "``add``" methods to add
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	442 information about various potentially aliasing instructions in the scope you are
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	443 interested in. Once all of the alias sets are completed, your pass should
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	444 simply iterate through the constructed alias sets, using the ``AliasSetTracker``
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	445 ``begin()``/``end()`` methods.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	446
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	447 The ``AliasSet``\s formed by the ``AliasSetTracker`` are guaranteed to be
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	448 disjoint, calculate mod/ref information and volatility for the set, and keep
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	449 track of whether or not all of the pointers in the set are Must aliases. The
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	450 AliasSetTracker also makes sure that sets are properly folded due to call
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	451 instructions, and can provide a list of pointers in each set.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	452
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	453 As an example user of this, the `Loop Invariant Code Motion
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	454 <doxygen/structLICM.html>`_ pass uses ``AliasSetTracker``\s to calculate alias
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	455 sets for each loop nest. If an ``AliasSet`` in a loop is not modified, then all
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	456 load instructions from that set may be hoisted out of the loop. If any alias
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	457 sets are stored to and are must alias sets, then the stores may be sunk
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	458 to outside of the loop, promoting the memory location to a register for the
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	459 duration of the loop nest. Both of these transformations only apply if the
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	460 pointer argument is loop-invariant.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	461
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	462 The AliasSetTracker implementation
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	463 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	464
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	465 The AliasSetTracker class is implemented to be as efficient as possible. It
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	466 uses the union-find algorithm to efficiently merge AliasSets when a pointer is
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	467 inserted into the AliasSetTracker that aliases multiple sets. The primary data
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	468 structure is a hash table mapping pointers to the AliasSet they are in.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	469
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	470 The AliasSetTracker class must maintain a list of all of the LLVM ``Value*``\s
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	471 that are in each AliasSet. Since the hash table already has entries for each
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	472 LLVM ``Value*`` of interest, the AliasesSets thread the linked list through
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	473 these hash-table nodes to avoid having to allocate memory unnecessarily, and to
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	474 make merging alias sets extremely efficient (the linked list merge is constant
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	475 time).
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	476
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	477 You shouldn't need to understand these details if you are just a client of the
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	478 AliasSetTracker, but if you look at the code, hopefully this brief description
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	479 will help make sense of why things are designed the way they are.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	480
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	481 Using the ``AliasAnalysis`` interface directly
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	482 ----------------------------------------------
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	483
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	484 If neither of these utility class are what your pass needs, you should use the
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	485 interfaces exposed by the ``AliasAnalysis`` class directly. Try to use the
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	486 higher-level methods when possible (e.g., use mod/ref information instead of the
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	487 `alias`_ method directly if possible) to get the best precision and efficiency.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	488
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	489 Existing alias analysis implementations and clients
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	490 ===================================================
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	491
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	492 If you're going to be working with the LLVM alias analysis infrastructure, you
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	493 should know what clients and implementations of alias analysis are available.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	494 In particular, if you are implementing an alias analysis, you should be aware of
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	495 the `the clients`_ that are useful for monitoring and evaluating different
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	496 implementations.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	497
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	498 .. _various alias analysis implementations:
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	499
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	500 Available ``AliasAnalysis`` implementations
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	501 -------------------------------------------
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	502
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	503 This section lists the various implementations of the ``AliasAnalysis``
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	504 interface. With the exception of the :ref:`-no-aa <aliasanalysis-no-aa>`
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	505 implementation, all of these :ref:`chain <aliasanalysis-chaining>` to other
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	506 alias analysis implementations.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	507
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	508 .. _aliasanalysis-no-aa:
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	509
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	510 The ``-no-aa`` pass
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	511 ^^^^^^^^^^^^^^^^^^^
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	512
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	513 The ``-no-aa`` pass is just like what it sounds: an alias analysis that never
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	514 returns any useful information. This pass can be useful if you think that alias
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	515 analysis is doing something wrong and are trying to narrow down a problem.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	516
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	517 The ``-basicaa`` pass
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	518 ^^^^^^^^^^^^^^^^^^^^^
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	519
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	520 The ``-basicaa`` pass is an aggressive local analysis that knows many
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	521 important facts:
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	522
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	523 * Distinct globals, stack allocations, and heap allocations can never alias.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	524 * Globals, stack allocations, and heap allocations never alias the null pointer.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	525 * Different fields of a structure do not alias.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	526 * Indexes into arrays with statically differing subscripts cannot alias.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	527 * Many common standard C library functions `never access memory or only read
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	528 memory`_.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	529 * Pointers that obviously point to constant globals "``pointToConstantMemory``".
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	530 * Function calls can not modify or references stack allocations if they never
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	531 escape from the function that allocates them (a common case for automatic
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	532 arrays).
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	533
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	534 The ``-globalsmodref-aa`` pass
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	535 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	536
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	537 This pass implements a simple context-sensitive mod/ref and alias analysis for
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	538 internal global variables that don't "have their address taken". If a global
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	539 does not have its address taken, the pass knows that no pointers alias the
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	540 global. This pass also keeps track of functions that it knows never access
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	541 memory or never read memory. This allows certain optimizations (e.g. GVN) to
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	542 eliminate call instructions entirely.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	543
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	544 The real power of this pass is that it provides context-sensitive mod/ref
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	545 information for call instructions. This allows the optimizer to know that calls
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	546 to a function do not clobber or read the value of the global, allowing loads and
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	547 stores to be eliminated.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	548
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	549 .. note::
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	550
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	551 This pass is somewhat limited in its scope (only support non-address taken
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	552 globals), but is very quick analysis.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	553
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	554 The ``-steens-aa`` pass
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	555 ^^^^^^^^^^^^^^^^^^^^^^^
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	556
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	557 The ``-steens-aa`` pass implements a variation on the well-known "Steensgaard's
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	558 algorithm" for interprocedural alias analysis. Steensgaard's algorithm is a
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	559 unification-based, flow-insensitive, context-insensitive, and field-insensitive
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	560 alias analysis that is also very scalable (effectively linear time).
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	561
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	562 The LLVM ``-steens-aa`` pass implements a "speculatively field-sensitive"
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	563 version of Steensgaard's algorithm using the Data Structure Analysis framework.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	564 This gives it substantially more precision than the standard algorithm while
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	565 maintaining excellent analysis scalability.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	566
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	567 .. note::
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	568
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	569 ``-steens-aa`` is available in the optional "poolalloc" module. It is not part
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	570 of the LLVM core.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	571
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	572 The ``-ds-aa`` pass
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	573 ^^^^^^^^^^^^^^^^^^^
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	574
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	575 The ``-ds-aa`` pass implements the full Data Structure Analysis algorithm. Data
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	576 Structure Analysis is a modular unification-based, flow-insensitive,
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	577 context-sensitive, and speculatively field-sensitive alias
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	578 analysis that is also quite scalable, usually at ``O(n * log(n))``.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	579
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	580 This algorithm is capable of responding to a full variety of alias analysis
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	581 queries, and can provide context-sensitive mod/ref information as well. The
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	582 only major facility not implemented so far is support for must-alias
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	583 information.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	584
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	585 .. note::
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	586
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	587 ``-ds-aa`` is available in the optional "poolalloc" module. It is not part of
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	588 the LLVM core.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	589
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	590 The ``-scev-aa`` pass
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	591 ^^^^^^^^^^^^^^^^^^^^^
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	592
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	593 The ``-scev-aa`` pass implements AliasAnalysis queries by translating them into
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	594 ScalarEvolution queries. This gives it a more complete understanding of
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	595 ``getelementptr`` instructions and loop induction variables than other alias
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	596 analyses have.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	597
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	598 Alias analysis driven transformations
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	599 -------------------------------------
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	600
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	601 LLVM includes several alias-analysis driven transformations which can be used
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	602 with any of the implementations above.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	603
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	604 The ``-adce`` pass
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	605 ^^^^^^^^^^^^^^^^^^
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	606
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	607 The ``-adce`` pass, which implements Aggressive Dead Code Elimination uses the
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	608 ``AliasAnalysis`` interface to delete calls to functions that do not have
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	609 side-effects and are not used.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	610
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	611 The ``-licm`` pass
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	612 ^^^^^^^^^^^^^^^^^^
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	613
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	614 The ``-licm`` pass implements various Loop Invariant Code Motion related
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	615 transformations. It uses the ``AliasAnalysis`` interface for several different
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	616 transformations:
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	617
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	618 * It uses mod/ref information to hoist or sink load instructions out of loops if
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	619 there are no instructions in the loop that modifies the memory loaded.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	620
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	621 * It uses mod/ref information to hoist function calls out of loops that do not
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	622 write to memory and are loop-invariant.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	623
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	624 * If uses alias information to promote memory objects that are loaded and stored
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	625 to in loops to live in a register instead. It can do this if there are no may
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	626 aliases to the loaded/stored memory location.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	627
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	628 The ``-argpromotion`` pass
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	629 ^^^^^^^^^^^^^^^^^^^^^^^^^^
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	630
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	631 The ``-argpromotion`` pass promotes by-reference arguments to be passed in
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	632 by-value instead. In particular, if pointer arguments are only loaded from it
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	633 passes in the value loaded instead of the address to the function. This pass
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	634 uses alias information to make sure that the value loaded from the argument
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	635 pointer is not modified between the entry of the function and any load of the
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	636 pointer.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	637
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	638 The ``-gvn``, ``-memcpyopt``, and ``-dse`` passes
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	639 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	640
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	641 These passes use AliasAnalysis information to reason about loads and stores.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	642
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	643 .. _the clients:
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	644
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	645 Clients for debugging and evaluation of implementations
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	646 -------------------------------------------------------
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	647
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	648 These passes are useful for evaluating the various alias analysis
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	649 implementations. You can use them with commands like:
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	650
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	651 .. code-block:: bash
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	652
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	653 % opt -ds-aa -aa-eval foo.bc -disable-output -stats
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	654
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	655 The ``-print-alias-sets`` pass
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	656 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	657
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	658 The ``-print-alias-sets`` pass is exposed as part of the ``opt`` tool to print
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	659 out the Alias Sets formed by the `AliasSetTracker`_ class. This is useful if
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	660 you're using the ``AliasSetTracker`` class. To use it, use something like:
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	661
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	662 .. code-block:: bash
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	663
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	664 % opt -ds-aa -print-alias-sets -disable-output
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	665
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	666 The ``-count-aa`` pass
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	667 ^^^^^^^^^^^^^^^^^^^^^^
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	668
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	669 The ``-count-aa`` pass is useful to see how many queries a particular pass is
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	670 making and what responses are returned by the alias analysis. As an example:
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	671
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	672 .. code-block:: bash
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	673
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	674 % opt -basicaa -count-aa -ds-aa -count-aa -licm
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	675
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	676 will print out how many queries (and what responses are returned) by the
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	677 ``-licm`` pass (of the ``-ds-aa`` pass) and how many queries are made of the
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	678 ``-basicaa`` pass by the ``-ds-aa`` pass. This can be useful when debugging a
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	679 transformation or an alias analysis implementation.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	680
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	681 The ``-aa-eval`` pass
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	682 ^^^^^^^^^^^^^^^^^^^^^
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	683
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	684 The ``-aa-eval`` pass simply iterates through all pairs of pointers in a
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	685 function and asks an alias analysis whether or not the pointers alias. This
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	686 gives an indication of the precision of the alias analysis. Statistics are
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	687 printed indicating the percent of no/may/must aliases found (a more precise
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	688 algorithm will have a lower number of may aliases).
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	689
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	690 Memory Dependence Analysis
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	691 ==========================
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	692
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	693 If you're just looking to be a client of alias analysis information, consider
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	694 using the Memory Dependence Analysis interface instead. MemDep is a lazy,
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	695 caching layer on top of alias analysis that is able to answer the question of
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	696 what preceding memory operations a given instruction depends on, either at an
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	697 intra- or inter-block level. Because of its laziness and caching policy, using
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	698 MemDep can be a significant performance win over accessing alias analysis
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	699 directly.

Mercurial > hg > CbC > CbC_llvm

annotate docs/AliasAnalysis.rst @ 18:5abb684876c4