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reorgnization done
author Shinji KONO <kono@ie.u-ryukyu.ac.jp>
date Mon, 25 May 2020 11:55:54 +0900
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1 <!--===- documentation/Overview.md
2
3 Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 See https://llvm.org/LICENSE.txt for license information.
5 SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6
7 -->
8
9 # Overview of Compiler Phases
10
11 Each phase produces either correct output or fatal errors.
12
13 ## Prescan and Preprocess
14
15 See: [Preprocessing.md](Preprocessing.md).
16
17 **Input:** Fortran source and header files, command line macro definitions,
18 set of enabled compiler directives (to be treated as directives rather than
19 comments).
20
21 **Output:**
22 - A "cooked" character stream: the entire program as a contiguous stream of
23 normalized Fortran source.
24 Extraneous whitespace and comments are removed (except comments that are
25 compiler directives that are not disabled) and case is normalized.
26 - Provenance information mapping each character back to the source it came from.
27 This is used in subsequent phases to issue errors messages that refer to source locations.
28
29 **Entry point:** `parser::Parsing::Prescan`
30
31 **Command:** `f18 -E src.f90` dumps the cooked character stream
32
33 ## Parse
34
35 **Input:** Cooked character stream.
36
37 **Output:** A parse tree representing a syntactically correct program,
38 rooted at a `parser::Program`.
39 See: [Parsing.md](Parsing.md) and [ParserCombinators.md](ParserCombinators.md).
40
41 **Entry point:** `parser::Parsing::Parse`
42
43 **Command:**
44 - `f18 -fdebug-dump-parse-tree -fparse-only src.f90` dumps the parse tree
45 - `f18 -funparse src.f90` converts the parse tree to normalized Fortran
46
47 ## Validate Labels and Canonicalize Do Statements
48
49 **Input:** Parse tree.
50
51 **Output:** The parse tree with label constraints and construct names checked,
52 and each `LabelDoStmt` converted to a `NonLabelDoStmt`.
53 See: [LabelResolution.md](LabelResolution.md).
54
55 **Entry points:** `semantics::ValidateLabels`, `parser::CanonicalizeDo`
56
57 ## Resolve Names
58
59 **Input:** Parse tree (without `LabelDoStmt`) and `.mod` files from compilation
60 of USEd modules.
61
62 **Output:**
63 - Tree of scopes populated with symbols and types
64 - Parse tree with some refinements:
65 - each `parser::Name::symbol` field points to one of the symbols
66 - each `parser::TypeSpec::declTypeSpec` field points to one of the types
67 - array element references that were parsed as function references or
68 statement functions are corrected
69
70 **Entry points:** `semantics::ResolveNames`, `semantics::RewriteParseTree`
71
72 **Command:** `f18 -fdebug-dump-symbols -fparse-only src.f90` dumps the
73 tree of scopes and symbols in each scope
74
75 ## Check DO CONCURRENT Constraints
76
77 **Input:** Parse tree with names resolved.
78
79 **Output:** Parse tree with semantically correct DO CONCURRENT loops.
80
81 ## Write Module Files
82
83 **Input:** Parse tree with names resolved.
84
85 **Output:** For each module and submodule, a `.mod` file containing a minimal
86 Fortran representation suitable for compiling program units that depend on it.
87 See [ModFiles.md](ModFiles.md).
88
89 ## Analyze Expressions and Assignments
90
91 **Input:** Parse tree with names resolved.
92
93 **Output:** Parse tree with `parser::Expr::typedExpr` filled in and semantic
94 checks performed on all expressions and assignment statements.
95
96 **Entry points**: `semantics::AnalyzeExpressions`, `semantics::AnalyzeAssignments`
97
98 ## Produce the Intermediate Representation
99
100 **Input:** Parse tree with names and labels resolved.
101
102 **Output:** An intermediate representation of the executable program.
103 See [FortranIR.md](FortranIR.md).