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comparison docs/AddingConstrainedIntrinsics.rst @ 148:63bd29f05246

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merged
author Shinji KONO <kono@ie.u-ryukyu.ac.jp>
date Wed, 14 Aug 2019 19:46:37 +0900
parents c2174574ed3a
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146:3fc4d5c3e21e 148:63bd29f05246
1 ==================================================
2 How To Add A Constrained Floating-Point Intrinsic
3 ==================================================
4
5 .. contents::
6 :local:
7
8 .. warning::
9 This is a work in progress.
10
11 Add the intrinsic
12 =================
13
14 Multiple files need to be updated when adding a new constrained intrinsic.
15
16 Add the new intrinsic to the table of intrinsics.::
17
18 include/llvm/IR/Intrinsics.td
19
20 Update class ConstrainedFPIntrinsic to know about the intrinsics.::
21
22 include/llvm/IR/IntrinsicInst.h
23
24 Functions like ConstrainedFPIntrinsic::isUnaryOp() or
25 ConstrainedFPIntrinsic::isTernaryOp() may need to know about the new
26 intrinsic.::
27
28 lib/IR/IntrinsicInst.cpp
29
30 Update the IR verifier::
31
32 lib/IR/Verifier.cpp
33
34 Add SelectionDAG node types
35 ===========================
36
37 Add the new STRICT version of the node type to the ISD::NodeType enum.::
38
39 include/llvm/CodeGen/ISDOpcodes.h
40
41 In class SDNode update isStrictFPOpcode()::
42
43 include/llvm/CodeGen/SelectionDAGNodes.h
44
45 A mapping from the STRICT SDnode type to the non-STRICT is done in
46 TargetLoweringBase::getStrictFPOperationAction(). This allows STRICT
47 nodes to be legalized similarly to the non-STRICT node type.::
48
49 include/llvm/CodeGen/TargetLowering.h
50
51 Building the SelectionDAG
52 -------------------------
53
54 The switch statement in SelectionDAGBuilder::visitIntrinsicCall() needs
55 to be updated to call SelectionDAGBuilder::visitConstrainedFPIntrinsic().
56 That function, in turn, needs to be updated to know how to create the
57 SDNode for the intrinsic. The new STRICT node will eventually be converted
58 to the matching non-STRICT node. For this reason it should have the same
59 operands and values as the non-STRICT version but should also use the chain.
60 This makes subsequent sharing of code for STRICT and non-STRICT code paths
61 easier.::
62
63 lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
64
65 Most of the STRICT nodes get legalized the same as their matching non-STRICT
66 counterparts. A new STRICT node with this property must get added to the
67 switch in SelectionDAGLegalize::LegalizeOp().::
68
69 lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
70
71 Other parts of the legalizer may need to be updated as well. Look for
72 places where the non-STRICT counterpart is legalized and update as needed.
73 Be careful of the chain since STRICT nodes use it but their counterparts
74 often don't.
75
76 The code to do the conversion or mutation of the STRICT node to a non-STRICT
77 version of the node happens in SelectionDAG::mutateStrictFPToFP(). Be
78 careful updating this function since some nodes have the same return type
79 as their input operand, but some are different. Both of these cases must
80 be properly handled.::
81
82 lib/CodeGen/SelectionDAG/SelectionDAG.cpp
83
84 However, the mutation may not happen if the new node has not been registered
85 in TargetLoweringBase::initActions(). If the corresponding non-STRICT node
86 is Legal but a target does not know about STRICT nodes then the STRICT
87 node will default to Legal and mutation will be bypassed with a "Cannot
88 select" error. Register the new STRICT node as Expand to avoid this bug.::
89
90 lib/CodeGen/TargetLoweringBase.cpp
91
92 To make debug logs readable it is helpful to update the SelectionDAG's
93 debug logger:::
94
95 lib/CodeGen/SelectionDAG/SelectionDAGDumper.cpp
96
97 Add documentation and tests
98 ===========================
99
100 ::
101
102 docs/LangRef.rst