1 //===- LoopRotation.cpp - Loop Rotation Pass ------------------------------===//
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 // This file implements Loop Rotation Pass.
10 //
11 //===----------------------------------------------------------------------===//
12
13 #include "llvm/Transforms/Scalar/LoopRotation.h"
14 #include "llvm/ADT/Statistic.h"
15 #include "llvm/Analysis/AssumptionCache.h"
16 #include "llvm/Analysis/InstructionSimplify.h"
17 #include "llvm/Analysis/LoopPass.h"
18 #include "llvm/Analysis/MemorySSA.h"
19 #include "llvm/Analysis/MemorySSAUpdater.h"
20 #include "llvm/Analysis/ScalarEvolution.h"
21 #include "llvm/Analysis/TargetTransformInfo.h"
22 #include "llvm/InitializePasses.h"
23 #include "llvm/Support/CommandLine.h"
24 #include "llvm/Support/Debug.h"
25 #include "llvm/Transforms/Scalar.h"
26 #include "llvm/Transforms/Scalar/LoopPassManager.h"
27 #include "llvm/Transforms/Utils/LoopRotationUtils.h"
28 #include "llvm/Transforms/Utils/LoopUtils.h"
29 using namespace llvm;
30
31 #define DEBUG_TYPE "loop-rotate"
32
33 static cl::opt<unsigned> DefaultRotationThreshold(
34 "rotation-max-header-size", cl::init(16), cl::Hidden,
35 cl::desc("The default maximum header size for automatic loop rotation"));
36
LoopRotatePass(bool EnableHeaderDuplication)37 LoopRotatePass::LoopRotatePass(bool EnableHeaderDuplication)
38 : EnableHeaderDuplication(EnableHeaderDuplication) {}
39
run(Loop & L,LoopAnalysisManager & AM,LoopStandardAnalysisResults & AR,LPMUpdater &)40 PreservedAnalyses LoopRotatePass::run(Loop &L, LoopAnalysisManager &AM,
41 LoopStandardAnalysisResults &AR,
42 LPMUpdater &) {
43 // Vectorization requires loop-rotation. Use default threshold for loops the
44 // user explicitly marked for vectorization, even when header duplication is
45 // disabled.
46 int Threshold = EnableHeaderDuplication ||
47 hasVectorizeTransformation(&L) == TM_ForcedByUser
48 ? DefaultRotationThreshold
49 : 0;
50 const DataLayout &DL = L.getHeader()->getModule()->getDataLayout();
51 const SimplifyQuery SQ = getBestSimplifyQuery(AR, DL);
52
53 Optional<MemorySSAUpdater> MSSAU;
54 if (AR.MSSA)
55 MSSAU = MemorySSAUpdater(AR.MSSA);
56 bool Changed = LoopRotation(&L, &AR.LI, &AR.TTI, &AR.AC, &AR.DT, &AR.SE,
57 MSSAU.hasValue() ? MSSAU.getPointer() : nullptr,
58 SQ, false, Threshold, false);
59
60 if (!Changed)
61 return PreservedAnalyses::all();
62
63 if (AR.MSSA && VerifyMemorySSA)
64 AR.MSSA->verifyMemorySSA();
65
66 auto PA = getLoopPassPreservedAnalyses();
67 if (AR.MSSA)
68 PA.preserve<MemorySSAAnalysis>();
69 return PA;
70 }
71
72 namespace {
73
74 class LoopRotateLegacyPass : public LoopPass {
75 unsigned MaxHeaderSize;
76
77 public:
78 static char ID; // Pass ID, replacement for typeid
LoopRotateLegacyPass(int SpecifiedMaxHeaderSize=-1)79 LoopRotateLegacyPass(int SpecifiedMaxHeaderSize = -1) : LoopPass(ID) {
80 initializeLoopRotateLegacyPassPass(*PassRegistry::getPassRegistry());
81 if (SpecifiedMaxHeaderSize == -1)
82 MaxHeaderSize = DefaultRotationThreshold;
83 else
84 MaxHeaderSize = unsigned(SpecifiedMaxHeaderSize);
85 }
86
87 // LCSSA form makes instruction renaming easier.
getAnalysisUsage(AnalysisUsage & AU) const88 void getAnalysisUsage(AnalysisUsage &AU) const override {
89 AU.addRequired<AssumptionCacheTracker>();
90 AU.addRequired<TargetTransformInfoWrapperPass>();
91 if (EnableMSSALoopDependency)
92 AU.addPreserved<MemorySSAWrapperPass>();
93 getLoopAnalysisUsage(AU);
94 }
95
runOnLoop(Loop * L,LPPassManager & LPM)96 bool runOnLoop(Loop *L, LPPassManager &LPM) override {
97 if (skipLoop(L))
98 return false;
99 Function &F = *L->getHeader()->getParent();
100
101 auto *LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
102 const auto *TTI = &getAnalysis<TargetTransformInfoWrapperPass>().getTTI(F);
103 auto *AC = &getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
104 auto &DT = getAnalysis<DominatorTreeWrapperPass>().getDomTree();
105 auto &SE = getAnalysis<ScalarEvolutionWrapperPass>().getSE();
106 const SimplifyQuery SQ = getBestSimplifyQuery(*this, F);
107 Optional<MemorySSAUpdater> MSSAU;
108 if (EnableMSSALoopDependency) {
109 // Not requiring MemorySSA and getting it only if available will split
110 // the loop pass pipeline when LoopRotate is being run first.
111 auto *MSSAA = getAnalysisIfAvailable<MemorySSAWrapperPass>();
112 if (MSSAA)
113 MSSAU = MemorySSAUpdater(&MSSAA->getMSSA());
114 }
115 // Vectorization requires loop-rotation. Use default threshold for loops the
116 // user explicitly marked for vectorization, even when header duplication is
117 // disabled.
118 int Threshold = hasVectorizeTransformation(L) == TM_ForcedByUser
119 ? DefaultRotationThreshold
120 : MaxHeaderSize;
121
122 return LoopRotation(L, LI, TTI, AC, &DT, &SE,
123 MSSAU.hasValue() ? MSSAU.getPointer() : nullptr, SQ,
124 false, Threshold, false);
125 }
126 };
127 } // end namespace
128
129 char LoopRotateLegacyPass::ID = 0;
130 INITIALIZE_PASS_BEGIN(LoopRotateLegacyPass, "loop-rotate", "Rotate Loops",
131 false, false)
INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)132 INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
133 INITIALIZE_PASS_DEPENDENCY(LoopPass)
134 INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass)
135 INITIALIZE_PASS_DEPENDENCY(MemorySSAWrapperPass)
136 INITIALIZE_PASS_END(LoopRotateLegacyPass, "loop-rotate", "Rotate Loops", false,
137 false)
138
139 Pass *llvm::createLoopRotatePass(int MaxHeaderSize) {
140 return new LoopRotateLegacyPass(MaxHeaderSize);
141 }
142