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/InitializePasses.h"
22#include "llvm/Support/CommandLine.h"
23#include "llvm/Support/Debug.h"
24#include "llvm/Transforms/Scalar.h"
25#include "llvm/Transforms/Scalar/LoopPassManager.h"
26#include "llvm/Transforms/Utils/LoopRotationUtils.h"
27#include "llvm/Transforms/Utils/LoopUtils.h"
28using namespace llvm;
29
30#define DEBUG_TYPE "loop-rotate"
31
32static cl::opt<unsigned> DefaultRotationThreshold(
33    "rotation-max-header-size", cl::init(16), cl::Hidden,
34    cl::desc("The default maximum header size for automatic loop rotation"));
35
36LoopRotatePass::LoopRotatePass(bool EnableHeaderDuplication)
37    : EnableHeaderDuplication(EnableHeaderDuplication) {}
38
39PreservedAnalyses LoopRotatePass::run(Loop &L, LoopAnalysisManager &AM,
40                                      LoopStandardAnalysisResults &AR,
41                                      LPMUpdater &) {
42  int Threshold = EnableHeaderDuplication ? DefaultRotationThreshold : 0;
43  const DataLayout &DL = L.getHeader()->getModule()->getDataLayout();
44  const SimplifyQuery SQ = getBestSimplifyQuery(AR, DL);
45
46  Optional<MemorySSAUpdater> MSSAU;
47  if (AR.MSSA)
48    MSSAU = MemorySSAUpdater(AR.MSSA);
49  bool Changed = LoopRotation(&L, &AR.LI, &AR.TTI, &AR.AC, &AR.DT, &AR.SE,
50                              MSSAU.hasValue() ? MSSAU.getPointer() : nullptr,
51                              SQ, false, Threshold, false);
52
53  if (!Changed)
54    return PreservedAnalyses::all();
55
56  if (AR.MSSA && VerifyMemorySSA)
57    AR.MSSA->verifyMemorySSA();
58
59  auto PA = getLoopPassPreservedAnalyses();
60  if (AR.MSSA)
61    PA.preserve<MemorySSAAnalysis>();
62  return PA;
63}
64
65namespace {
66
67class LoopRotateLegacyPass : public LoopPass {
68  unsigned MaxHeaderSize;
69
70public:
71  static char ID; // Pass ID, replacement for typeid
72  LoopRotateLegacyPass(int SpecifiedMaxHeaderSize = -1) : LoopPass(ID) {
73    initializeLoopRotateLegacyPassPass(*PassRegistry::getPassRegistry());
74    if (SpecifiedMaxHeaderSize == -1)
75      MaxHeaderSize = DefaultRotationThreshold;
76    else
77      MaxHeaderSize = unsigned(SpecifiedMaxHeaderSize);
78  }
79
80  // LCSSA form makes instruction renaming easier.
81  void getAnalysisUsage(AnalysisUsage &AU) const override {
82    AU.addRequired<AssumptionCacheTracker>();
83    AU.addRequired<TargetTransformInfoWrapperPass>();
84    if (EnableMSSALoopDependency)
85      AU.addPreserved<MemorySSAWrapperPass>();
86    getLoopAnalysisUsage(AU);
87  }
88
89  bool runOnLoop(Loop *L, LPPassManager &LPM) override {
90    if (skipLoop(L))
91      return false;
92    Function &F = *L->getHeader()->getParent();
93
94    auto *LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
95    const auto *TTI = &getAnalysis<TargetTransformInfoWrapperPass>().getTTI(F);
96    auto *AC = &getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
97    auto &DT = getAnalysis<DominatorTreeWrapperPass>().getDomTree();
98    auto &SE = getAnalysis<ScalarEvolutionWrapperPass>().getSE();
99    const SimplifyQuery SQ = getBestSimplifyQuery(*this, F);
100    Optional<MemorySSAUpdater> MSSAU;
101    if (EnableMSSALoopDependency) {
102      // Not requiring MemorySSA and getting it only if available will split
103      // the loop pass pipeline when LoopRotate is being run first.
104      auto *MSSAA = getAnalysisIfAvailable<MemorySSAWrapperPass>();
105      if (MSSAA)
106        MSSAU = MemorySSAUpdater(&MSSAA->getMSSA());
107    }
108    return LoopRotation(L, LI, TTI, AC, &DT, &SE,
109                        MSSAU.hasValue() ? MSSAU.getPointer() : nullptr, SQ,
110                        false, MaxHeaderSize, false);
111  }
112};
113}
114
115char LoopRotateLegacyPass::ID = 0;
116INITIALIZE_PASS_BEGIN(LoopRotateLegacyPass, "loop-rotate", "Rotate Loops",
117                      false, false)
118INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
119INITIALIZE_PASS_DEPENDENCY(LoopPass)
120INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass)
121INITIALIZE_PASS_DEPENDENCY(MemorySSAWrapperPass)
122INITIALIZE_PASS_END(LoopRotateLegacyPass, "loop-rotate", "Rotate Loops", false,
123                    false)
124
125Pass *llvm::createLoopRotatePass(int MaxHeaderSize) {
126  return new LoopRotateLegacyPass(MaxHeaderSize);
127}
128