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 
37 LoopRotatePass::LoopRotatePass(bool EnableHeaderDuplication)
38     : EnableHeaderDuplication(EnableHeaderDuplication) {}
39 
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
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.
88   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 
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)
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