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/Analysis/AssumptionCache.h"
15 #include "llvm/Analysis/InstructionSimplify.h"
16 #include "llvm/Analysis/LazyBlockFrequencyInfo.h"
17 #include "llvm/Analysis/LoopInfo.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/Transforms/Scalar.h"
26 #include "llvm/Transforms/Utils/LoopRotationUtils.h"
27 #include "llvm/Transforms/Utils/LoopUtils.h"
28 #include <optional>
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
37 static cl::opt<bool> PrepareForLTOOption(
38 "rotation-prepare-for-lto", cl::init(false), cl::Hidden,
39 cl::desc("Run loop-rotation in the prepare-for-lto stage. This option "
40 "should be used for testing only."));
41
LoopRotatePass(bool EnableHeaderDuplication,bool PrepareForLTO)42 LoopRotatePass::LoopRotatePass(bool EnableHeaderDuplication, bool PrepareForLTO)
43 : EnableHeaderDuplication(EnableHeaderDuplication),
44 PrepareForLTO(PrepareForLTO) {}
45
printPipeline(raw_ostream & OS,function_ref<StringRef (StringRef)> MapClassName2PassName)46 void LoopRotatePass::printPipeline(
47 raw_ostream &OS, function_ref<StringRef(StringRef)> MapClassName2PassName) {
48 static_cast<PassInfoMixin<LoopRotatePass> *>(this)->printPipeline(
49 OS, MapClassName2PassName);
50 OS << "<";
51 if (!EnableHeaderDuplication)
52 OS << "no-";
53 OS << "header-duplication;";
54
55 if (!PrepareForLTO)
56 OS << "no-";
57 OS << "prepare-for-lto";
58 OS << ">";
59 }
60
run(Loop & L,LoopAnalysisManager & AM,LoopStandardAnalysisResults & AR,LPMUpdater &)61 PreservedAnalyses LoopRotatePass::run(Loop &L, LoopAnalysisManager &AM,
62 LoopStandardAnalysisResults &AR,
63 LPMUpdater &) {
64 // Vectorization requires loop-rotation. Use default threshold for loops the
65 // user explicitly marked for vectorization, even when header duplication is
66 // disabled.
67 int Threshold = EnableHeaderDuplication ||
68 hasVectorizeTransformation(&L) == TM_ForcedByUser
69 ? DefaultRotationThreshold
70 : 0;
71 const DataLayout &DL = L.getHeader()->getModule()->getDataLayout();
72 const SimplifyQuery SQ = getBestSimplifyQuery(AR, DL);
73
74 std::optional<MemorySSAUpdater> MSSAU;
75 if (AR.MSSA)
76 MSSAU = MemorySSAUpdater(AR.MSSA);
77 bool Changed = LoopRotation(&L, &AR.LI, &AR.TTI, &AR.AC, &AR.DT, &AR.SE,
78 MSSAU ? &*MSSAU : nullptr, SQ, false, Threshold,
79 false, PrepareForLTO || PrepareForLTOOption);
80
81 if (!Changed)
82 return PreservedAnalyses::all();
83
84 if (AR.MSSA && VerifyMemorySSA)
85 AR.MSSA->verifyMemorySSA();
86
87 auto PA = getLoopPassPreservedAnalyses();
88 if (AR.MSSA)
89 PA.preserve<MemorySSAAnalysis>();
90 return PA;
91 }
92
93 namespace {
94
95 class LoopRotateLegacyPass : public LoopPass {
96 unsigned MaxHeaderSize;
97 bool PrepareForLTO;
98
99 public:
100 static char ID; // Pass ID, replacement for typeid
LoopRotateLegacyPass(int SpecifiedMaxHeaderSize=-1,bool PrepareForLTO=false)101 LoopRotateLegacyPass(int SpecifiedMaxHeaderSize = -1,
102 bool PrepareForLTO = false)
103 : LoopPass(ID), PrepareForLTO(PrepareForLTO) {
104 initializeLoopRotateLegacyPassPass(*PassRegistry::getPassRegistry());
105 if (SpecifiedMaxHeaderSize == -1)
106 MaxHeaderSize = DefaultRotationThreshold;
107 else
108 MaxHeaderSize = unsigned(SpecifiedMaxHeaderSize);
109 }
110
111 // LCSSA form makes instruction renaming easier.
getAnalysisUsage(AnalysisUsage & AU) const112 void getAnalysisUsage(AnalysisUsage &AU) const override {
113 AU.addRequired<AssumptionCacheTracker>();
114 AU.addRequired<TargetTransformInfoWrapperPass>();
115 AU.addPreserved<MemorySSAWrapperPass>();
116 getLoopAnalysisUsage(AU);
117
118 // Lazy BFI and BPI are marked as preserved here so LoopRotate
119 // can remain part of the same loop pass manager as LICM.
120 AU.addPreserved<LazyBlockFrequencyInfoPass>();
121 AU.addPreserved<LazyBranchProbabilityInfoPass>();
122 }
123
runOnLoop(Loop * L,LPPassManager & LPM)124 bool runOnLoop(Loop *L, LPPassManager &LPM) override {
125 if (skipLoop(L))
126 return false;
127 Function &F = *L->getHeader()->getParent();
128
129 auto *LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
130 const auto *TTI = &getAnalysis<TargetTransformInfoWrapperPass>().getTTI(F);
131 auto *AC = &getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
132 auto &DT = getAnalysis<DominatorTreeWrapperPass>().getDomTree();
133 auto &SE = getAnalysis<ScalarEvolutionWrapperPass>().getSE();
134 const SimplifyQuery SQ = getBestSimplifyQuery(*this, F);
135 std::optional<MemorySSAUpdater> MSSAU;
136 // Not requiring MemorySSA and getting it only if available will split
137 // the loop pass pipeline when LoopRotate is being run first.
138 auto *MSSAA = getAnalysisIfAvailable<MemorySSAWrapperPass>();
139 if (MSSAA)
140 MSSAU = MemorySSAUpdater(&MSSAA->getMSSA());
141 // Vectorization requires loop-rotation. Use default threshold for loops the
142 // user explicitly marked for vectorization, even when header duplication is
143 // disabled.
144 int Threshold = hasVectorizeTransformation(L) == TM_ForcedByUser
145 ? DefaultRotationThreshold
146 : MaxHeaderSize;
147
148 return LoopRotation(L, LI, TTI, AC, &DT, &SE, MSSAU ? &*MSSAU : nullptr, SQ,
149 false, Threshold, false,
150 PrepareForLTO || PrepareForLTOOption);
151 }
152 };
153 } // end namespace
154
155 char LoopRotateLegacyPass::ID = 0;
156 INITIALIZE_PASS_BEGIN(LoopRotateLegacyPass, "loop-rotate", "Rotate Loops",
157 false, false)
INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)158 INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
159 INITIALIZE_PASS_DEPENDENCY(LoopPass)
160 INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass)
161 INITIALIZE_PASS_DEPENDENCY(MemorySSAWrapperPass)
162 INITIALIZE_PASS_END(LoopRotateLegacyPass, "loop-rotate", "Rotate Loops", false,
163 false)
164
165 Pass *llvm::createLoopRotatePass(int MaxHeaderSize, bool PrepareForLTO) {
166 return new LoopRotateLegacyPass(MaxHeaderSize, PrepareForLTO);
167 }
168