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/InstructionSimplify.h"
16 #include "llvm/Analysis/LoopPass.h"
17 #include "llvm/Analysis/MemorySSA.h"
18 #include "llvm/Analysis/MemorySSAUpdater.h"
19 #include "llvm/Analysis/ScalarEvolution.h"
20 #include "llvm/Analysis/TargetTransformInfo.h"
21 #include "llvm/Support/Debug.h"
22 #include "llvm/Transforms/Scalar.h"
23 #include "llvm/Transforms/Scalar/LoopPassManager.h"
24 #include "llvm/Transforms/Utils/LoopRotationUtils.h"
25 #include "llvm/Transforms/Utils/LoopUtils.h"
26 using namespace llvm;
27 
28 #define DEBUG_TYPE "loop-rotate"
29 
30 static cl::opt<unsigned> DefaultRotationThreshold(
31     "rotation-max-header-size", cl::init(16), cl::Hidden,
32     cl::desc("The default maximum header size for automatic loop rotation"));
33 
34 LoopRotatePass::LoopRotatePass(bool EnableHeaderDuplication)
35     : EnableHeaderDuplication(EnableHeaderDuplication) {}
36 
37 PreservedAnalyses LoopRotatePass::run(Loop &L, LoopAnalysisManager &AM,
38                                       LoopStandardAnalysisResults &AR,
39                                       LPMUpdater &) {
40   int Threshold = EnableHeaderDuplication ? DefaultRotationThreshold : 0;
41   const DataLayout &DL = L.getHeader()->getModule()->getDataLayout();
42   const SimplifyQuery SQ = getBestSimplifyQuery(AR, DL);
43 
44   Optional<MemorySSAUpdater> MSSAU;
45   if (AR.MSSA)
46     MSSAU = MemorySSAUpdater(AR.MSSA);
47   bool Changed = LoopRotation(&L, &AR.LI, &AR.TTI, &AR.AC, &AR.DT, &AR.SE,
48                               MSSAU.hasValue() ? MSSAU.getPointer() : nullptr,
49                               SQ, false, Threshold, false);
50 
51   if (!Changed)
52     return PreservedAnalyses::all();
53 
54   if (AR.MSSA && VerifyMemorySSA)
55     AR.MSSA->verifyMemorySSA();
56 
57   return getLoopPassPreservedAnalyses();
58 }
59 
60 namespace {
61 
62 class LoopRotateLegacyPass : public LoopPass {
63   unsigned MaxHeaderSize;
64 
65 public:
66   static char ID; // Pass ID, replacement for typeid
67   LoopRotateLegacyPass(int SpecifiedMaxHeaderSize = -1) : LoopPass(ID) {
68     initializeLoopRotateLegacyPassPass(*PassRegistry::getPassRegistry());
69     if (SpecifiedMaxHeaderSize == -1)
70       MaxHeaderSize = DefaultRotationThreshold;
71     else
72       MaxHeaderSize = unsigned(SpecifiedMaxHeaderSize);
73   }
74 
75   // LCSSA form makes instruction renaming easier.
76   void getAnalysisUsage(AnalysisUsage &AU) const override {
77     AU.addRequired<AssumptionCacheTracker>();
78     AU.addRequired<TargetTransformInfoWrapperPass>();
79     if (EnableMSSALoopDependency) {
80       AU.addRequired<MemorySSAWrapperPass>();
81       AU.addPreserved<MemorySSAWrapperPass>();
82     }
83     getLoopAnalysisUsage(AU);
84   }
85 
86   bool runOnLoop(Loop *L, LPPassManager &LPM) override {
87     if (skipLoop(L))
88       return false;
89     Function &F = *L->getHeader()->getParent();
90 
91     auto *LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
92     const auto *TTI = &getAnalysis<TargetTransformInfoWrapperPass>().getTTI(F);
93     auto *AC = &getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
94     auto *DTWP = getAnalysisIfAvailable<DominatorTreeWrapperPass>();
95     auto *DT = DTWP ? &DTWP->getDomTree() : nullptr;
96     auto *SEWP = getAnalysisIfAvailable<ScalarEvolutionWrapperPass>();
97     auto *SE = SEWP ? &SEWP->getSE() : nullptr;
98     const SimplifyQuery SQ = getBestSimplifyQuery(*this, F);
99     Optional<MemorySSAUpdater> MSSAU;
100     if (EnableMSSALoopDependency) {
101       MemorySSA *MSSA = &getAnalysis<MemorySSAWrapperPass>().getMSSA();
102       MSSAU = MemorySSAUpdater(MSSA);
103     }
104     return LoopRotation(L, LI, TTI, AC, DT, SE,
105                         MSSAU.hasValue() ? MSSAU.getPointer() : nullptr, SQ,
106                         false, MaxHeaderSize, false);
107   }
108 };
109 }
110 
111 char LoopRotateLegacyPass::ID = 0;
112 INITIALIZE_PASS_BEGIN(LoopRotateLegacyPass, "loop-rotate", "Rotate Loops",
113                       false, false)
114 INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
115 INITIALIZE_PASS_DEPENDENCY(LoopPass)
116 INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass)
117 INITIALIZE_PASS_DEPENDENCY(MemorySSAWrapperPass)
118 INITIALIZE_PASS_END(LoopRotateLegacyPass, "loop-rotate", "Rotate Loops", false,
119                     false)
120 
121 Pass *llvm::createLoopRotatePass(int MaxHeaderSize) {
122   return new LoopRotateLegacyPass(MaxHeaderSize);
123 }
124