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/LazyBlockFrequencyInfo.h"
18 #include "llvm/Analysis/LoopPass.h"
19 #include "llvm/Analysis/MemorySSA.h"
20 #include "llvm/Analysis/MemorySSAUpdater.h"
21 #include "llvm/Analysis/ScalarEvolution.h"
22 #include "llvm/Analysis/TargetTransformInfo.h"
23 #include "llvm/InitializePasses.h"
24 #include "llvm/Support/CommandLine.h"
25 #include "llvm/Support/Debug.h"
26 #include "llvm/Transforms/Scalar.h"
27 #include "llvm/Transforms/Scalar/LoopPassManager.h"
28 #include "llvm/Transforms/Utils/LoopRotationUtils.h"
29 #include "llvm/Transforms/Utils/LoopUtils.h"
30 using namespace llvm;
31
32 #define DEBUG_TYPE "loop-rotate"
33
34 static cl::opt<unsigned> DefaultRotationThreshold(
35 "rotation-max-header-size", cl::init(16), cl::Hidden,
36 cl::desc("The default maximum header size for automatic loop rotation"));
37
38 static cl::opt<bool> PrepareForLTOOption(
39 "rotation-prepare-for-lto", cl::init(false), cl::Hidden,
40 cl::desc("Run loop-rotation in the prepare-for-lto stage. This option "
41 "should be used for testing only."));
42
LoopRotatePass(bool EnableHeaderDuplication,bool PrepareForLTO)43 LoopRotatePass::LoopRotatePass(bool EnableHeaderDuplication, bool PrepareForLTO)
44 : EnableHeaderDuplication(EnableHeaderDuplication),
45 PrepareForLTO(PrepareForLTO) {}
46
run(Loop & L,LoopAnalysisManager & AM,LoopStandardAnalysisResults & AR,LPMUpdater &)47 PreservedAnalyses LoopRotatePass::run(Loop &L, LoopAnalysisManager &AM,
48 LoopStandardAnalysisResults &AR,
49 LPMUpdater &) {
50 // Vectorization requires loop-rotation. Use default threshold for loops the
51 // user explicitly marked for vectorization, even when header duplication is
52 // disabled.
53 int Threshold = EnableHeaderDuplication ||
54 hasVectorizeTransformation(&L) == TM_ForcedByUser
55 ? DefaultRotationThreshold
56 : 0;
57 const DataLayout &DL = L.getHeader()->getModule()->getDataLayout();
58 const SimplifyQuery SQ = getBestSimplifyQuery(AR, DL);
59
60 Optional<MemorySSAUpdater> MSSAU;
61 if (AR.MSSA)
62 MSSAU = MemorySSAUpdater(AR.MSSA);
63 bool Changed =
64 LoopRotation(&L, &AR.LI, &AR.TTI, &AR.AC, &AR.DT, &AR.SE,
65 MSSAU.hasValue() ? MSSAU.getPointer() : nullptr, SQ, false,
66 Threshold, false, PrepareForLTO || PrepareForLTOOption);
67
68 if (!Changed)
69 return PreservedAnalyses::all();
70
71 if (AR.MSSA && VerifyMemorySSA)
72 AR.MSSA->verifyMemorySSA();
73
74 auto PA = getLoopPassPreservedAnalyses();
75 if (AR.MSSA)
76 PA.preserve<MemorySSAAnalysis>();
77 return PA;
78 }
79
80 namespace {
81
82 class LoopRotateLegacyPass : public LoopPass {
83 unsigned MaxHeaderSize;
84 bool PrepareForLTO;
85
86 public:
87 static char ID; // Pass ID, replacement for typeid
LoopRotateLegacyPass(int SpecifiedMaxHeaderSize=-1,bool PrepareForLTO=false)88 LoopRotateLegacyPass(int SpecifiedMaxHeaderSize = -1,
89 bool PrepareForLTO = false)
90 : LoopPass(ID), PrepareForLTO(PrepareForLTO) {
91 initializeLoopRotateLegacyPassPass(*PassRegistry::getPassRegistry());
92 if (SpecifiedMaxHeaderSize == -1)
93 MaxHeaderSize = DefaultRotationThreshold;
94 else
95 MaxHeaderSize = unsigned(SpecifiedMaxHeaderSize);
96 }
97
98 // LCSSA form makes instruction renaming easier.
getAnalysisUsage(AnalysisUsage & AU) const99 void getAnalysisUsage(AnalysisUsage &AU) const override {
100 AU.addRequired<AssumptionCacheTracker>();
101 AU.addRequired<TargetTransformInfoWrapperPass>();
102 if (EnableMSSALoopDependency)
103 AU.addPreserved<MemorySSAWrapperPass>();
104 getLoopAnalysisUsage(AU);
105
106 // Lazy BFI and BPI are marked as preserved here so LoopRotate
107 // can remain part of the same loop pass manager as LICM.
108 AU.addPreserved<LazyBlockFrequencyInfoPass>();
109 AU.addPreserved<LazyBranchProbabilityInfoPass>();
110 }
111
runOnLoop(Loop * L,LPPassManager & LPM)112 bool runOnLoop(Loop *L, LPPassManager &LPM) override {
113 if (skipLoop(L))
114 return false;
115 Function &F = *L->getHeader()->getParent();
116
117 auto *LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
118 const auto *TTI = &getAnalysis<TargetTransformInfoWrapperPass>().getTTI(F);
119 auto *AC = &getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
120 auto &DT = getAnalysis<DominatorTreeWrapperPass>().getDomTree();
121 auto &SE = getAnalysis<ScalarEvolutionWrapperPass>().getSE();
122 const SimplifyQuery SQ = getBestSimplifyQuery(*this, F);
123 Optional<MemorySSAUpdater> MSSAU;
124 if (EnableMSSALoopDependency) {
125 // Not requiring MemorySSA and getting it only if available will split
126 // the loop pass pipeline when LoopRotate is being run first.
127 auto *MSSAA = getAnalysisIfAvailable<MemorySSAWrapperPass>();
128 if (MSSAA)
129 MSSAU = MemorySSAUpdater(&MSSAA->getMSSA());
130 }
131 // Vectorization requires loop-rotation. Use default threshold for loops the
132 // user explicitly marked for vectorization, even when header duplication is
133 // disabled.
134 int Threshold = hasVectorizeTransformation(L) == TM_ForcedByUser
135 ? DefaultRotationThreshold
136 : MaxHeaderSize;
137
138 return LoopRotation(L, LI, TTI, AC, &DT, &SE,
139 MSSAU.hasValue() ? MSSAU.getPointer() : nullptr, SQ,
140 false, Threshold, false,
141 PrepareForLTO || PrepareForLTOOption);
142 }
143 };
144 } // end namespace
145
146 char LoopRotateLegacyPass::ID = 0;
147 INITIALIZE_PASS_BEGIN(LoopRotateLegacyPass, "loop-rotate", "Rotate Loops",
148 false, false)
INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)149 INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
150 INITIALIZE_PASS_DEPENDENCY(LoopPass)
151 INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass)
152 INITIALIZE_PASS_DEPENDENCY(MemorySSAWrapperPass)
153 INITIALIZE_PASS_END(LoopRotateLegacyPass, "loop-rotate", "Rotate Loops", false,
154 false)
155
156 Pass *llvm::createLoopRotatePass(int MaxHeaderSize, bool PrepareForLTO) {
157 return new LoopRotateLegacyPass(MaxHeaderSize, PrepareForLTO);
158 }
159