1 //===- LoopVersioning.h - Utility to version a loop -------------*- C++ -*-===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file defines a utility class to perform loop versioning. The versioned
11 // loop speculates that otherwise may-aliasing memory accesses don't overlap and
12 // emits checks to prove this.
14 //===----------------------------------------------------------------------===//
16 #ifndef LLVM_TRANSFORMS_UTILS_LOOPVERSIONING_H
17 #define LLVM_TRANSFORMS_UTILS_LOOPVERSIONING_H
19 #include "llvm/Analysis/LoopAccessAnalysis.h"
20 #include "llvm/Analysis/ScalarEvolution.h"
21 #include "llvm/Transforms/Utils/ValueMapper.h"
22 #include "llvm/Transforms/Utils/LoopUtils.h"
29 class ScalarEvolution;
31 /// \brief This class emits a version of the loop where run-time checks ensure
32 /// that may-alias pointers can't overlap.
34 /// It currently only supports single-exit loops and assumes that the loop
35 /// already has a preheader.
36 class LoopVersioning {
38 /// \brief Expects LoopAccessInfo, Loop, LoopInfo, DominatorTree as input.
39 /// It uses runtime check provided by the user. If \p UseLAIChecks is true,
40 /// we will retain the default checks made by LAI. Otherwise, construct an
41 /// object having no checks and we expect the user to add them.
42 LoopVersioning(const LoopAccessInfo &LAI, Loop *L, LoopInfo *LI,
43 DominatorTree *DT, ScalarEvolution *SE,
44 bool UseLAIChecks = true);
46 /// \brief Performs the CFG manipulation part of versioning the loop including
47 /// the DominatorTree and LoopInfo updates.
49 /// The loop that was used to construct the class will be the "versioned" loop
50 /// i.e. the loop that will receive control if all the memchecks pass.
52 /// This allows the loop transform pass to operate on the same loop regardless
53 /// of whether versioning was necessary or not:
57 /// if versioning is necessary version L
59 void versionLoop() { versionLoop(findDefsUsedOutsideOfLoop(VersionedLoop)); }
61 /// \brief Same but if the client has already precomputed the set of values
62 /// used outside the loop, this API will allows passing that.
63 void versionLoop(const SmallVectorImpl<Instruction *> &DefsUsedOutside);
65 /// \brief Returns the versioned loop. Control flows here if pointers in the
66 /// loop don't alias (i.e. all memchecks passed). (This loop is actually the
67 /// same as the original loop that we got constructed with.)
68 Loop *getVersionedLoop() { return VersionedLoop; }
70 /// \brief Returns the fall-back loop. Control flows here if pointers in the
71 /// loop may alias (i.e. one of the memchecks failed).
72 Loop *getNonVersionedLoop() { return NonVersionedLoop; }
74 /// \brief Sets the runtime alias checks for versioning the loop.
76 SmallVector<RuntimePointerChecking::PointerCheck, 4> Checks);
78 /// \brief Sets the runtime SCEV checks for versioning the loop.
79 void setSCEVChecks(SCEVUnionPredicate Check);
81 /// \brief Annotate memory instructions in the versioned loop with no-alias
82 /// metadata based on the memchecks issued.
84 /// This is just wrapper that calls prepareNoAliasMetadata and
85 /// annotateInstWithNoAlias on the instructions of the versioned loop.
86 void annotateLoopWithNoAlias();
88 /// \brief Set up the aliasing scopes based on the memchecks. This needs to
89 /// be called before the first call to annotateInstWithNoAlias.
90 void prepareNoAliasMetadata();
92 /// \brief Add the noalias annotations to \p VersionedInst.
94 /// \p OrigInst is the instruction corresponding to \p VersionedInst in the
95 /// original loop. Initialize the aliasing scopes with
96 /// prepareNoAliasMetadata once before this can be called.
97 void annotateInstWithNoAlias(Instruction *VersionedInst,
98 const Instruction *OrigInst);
101 /// \brief Adds the necessary PHI nodes for the versioned loops based on the
102 /// loop-defined values used outside of the loop.
104 /// This needs to be called after versionLoop if there are defs in the loop
105 /// that are used outside the loop.
106 void addPHINodes(const SmallVectorImpl<Instruction *> &DefsUsedOutside);
108 /// \brief Add the noalias annotations to \p I. Initialize the aliasing
109 /// scopes with prepareNoAliasMetadata once before this can be called.
110 void annotateInstWithNoAlias(Instruction *I) {
111 annotateInstWithNoAlias(I, I);
114 /// \brief The original loop. This becomes the "versioned" one. I.e.,
115 /// control flows here if pointers in the loop don't alias.
117 /// \brief The fall-back loop. I.e. control flows here if pointers in the
118 /// loop may alias (memchecks failed).
119 Loop *NonVersionedLoop;
121 /// \brief This maps the instructions from VersionedLoop to their counterpart
122 /// in NonVersionedLoop.
123 ValueToValueMapTy VMap;
125 /// \brief The set of alias checks that we are versioning for.
126 SmallVector<RuntimePointerChecking::PointerCheck, 4> AliasChecks;
128 /// \brief The set of SCEV checks that we are versioning for.
129 SCEVUnionPredicate Preds;
131 /// \brief Maps a pointer to the pointer checking group that the pointer
133 DenseMap<const Value *, const RuntimePointerChecking::CheckingPtrGroup *>
136 /// \brief The alias scope corresponding to a pointer checking group.
137 DenseMap<const RuntimePointerChecking::CheckingPtrGroup *, MDNode *>
140 /// \brief The list of alias scopes that a pointer checking group can't alias.
141 DenseMap<const RuntimePointerChecking::CheckingPtrGroup *, MDNode *>
142 GroupToNonAliasingScopeList;
144 /// \brief Analyses used.
145 const LoopAccessInfo &LAI;