InstSimplifyPass.cpp revision 360784 
1//===- InstSimplifyPass.cpp -----------------------------------------------===//
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#include "llvm/Transforms/Scalar/InstSimplifyPass.h"
10#include "llvm/ADT/DepthFirstIterator.h"
11#include "llvm/ADT/SmallPtrSet.h"
12#include "llvm/ADT/Statistic.h"
13#include "llvm/Analysis/AssumptionCache.h"
14#include "llvm/Analysis/InstructionSimplify.h"
15#include "llvm/Analysis/OptimizationRemarkEmitter.h"
16#include "llvm/Analysis/TargetLibraryInfo.h"
17#include "llvm/IR/DataLayout.h"
18#include "llvm/IR/Dominators.h"
19#include "llvm/IR/Function.h"
20#include "llvm/IR/Type.h"
21#include "llvm/InitializePasses.h"
22#include "llvm/Pass.h"
23#include "llvm/Transforms/Utils.h"
24#include "llvm/Transforms/Utils/Local.h"
25using namespace llvm;
26
27#define DEBUG_TYPE "instsimplify"
28
29STATISTIC(NumSimplified, "Number of redundant instructions removed");
30
31static bool runImpl(Function &F, const SimplifyQuery &SQ,
32                    OptimizationRemarkEmitter *ORE) {
33  SmallPtrSet<const Instruction *, 8> S1, S2, *ToSimplify = &S1, *Next = &S2;
34  bool Changed = false;
35
36  do {
37    for (BasicBlock &BB : F) {
38      // Unreachable code can take on strange forms that we are not prepared to
39      // handle. For example, an instruction may have itself as an operand.
40      if (!SQ.DT->isReachableFromEntry(&BB))
41        continue;
42
43      SmallVector<Instruction *, 8> DeadInstsInBB;
44      for (Instruction &I : BB) {
45        // The first time through the loop, ToSimplify is empty and we try to
46        // simplify all instructions. On later iterations, ToSimplify is not
47        // empty and we only bother simplifying instructions that are in it.
48        if (!ToSimplify->empty() && !ToSimplify->count(&I))
49          continue;
50
51        // Don't waste time simplifying dead/unused instructions.
52        if (isInstructionTriviallyDead(&I)) {
53          DeadInstsInBB.push_back(&I);
54          Changed = true;
55        } else if (!I.use_empty()) {
56          if (Value *V = SimplifyInstruction(&I, SQ, ORE)) {
57            // Mark all uses for resimplification next time round the loop.
58            for (User *U : I.users())
59              Next->insert(cast<Instruction>(U));
60            I.replaceAllUsesWith(V);
61            ++NumSimplified;
62            Changed = true;
63            // A call can get simplified, but it may not be trivially dead.
64            if (isInstructionTriviallyDead(&I))
65              DeadInstsInBB.push_back(&I);
66          }
67        }
68      }
69      RecursivelyDeleteTriviallyDeadInstructions(DeadInstsInBB, SQ.TLI);
70    }
71
72    // Place the list of instructions to simplify on the next loop iteration
73    // into ToSimplify.
74    std::swap(ToSimplify, Next);
75    Next->clear();
76  } while (!ToSimplify->empty());
77
78  return Changed;
79}
80
81namespace {
82struct InstSimplifyLegacyPass : public FunctionPass {
83  static char ID; // Pass identification, replacement for typeid
84  InstSimplifyLegacyPass() : FunctionPass(ID) {
85    initializeInstSimplifyLegacyPassPass(*PassRegistry::getPassRegistry());
86  }
87
88  void getAnalysisUsage(AnalysisUsage &AU) const override {
89    AU.setPreservesCFG();
90    AU.addRequired<DominatorTreeWrapperPass>();
91    AU.addRequired<AssumptionCacheTracker>();
92    AU.addRequired<TargetLibraryInfoWrapperPass>();
93    AU.addRequired<OptimizationRemarkEmitterWrapperPass>();
94  }
95
96  /// Remove instructions that simplify.
97  bool runOnFunction(Function &F) override {
98    if (skipFunction(F))
99      return false;
100
101    const DominatorTree *DT =
102        &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
103    const TargetLibraryInfo *TLI =
104        &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(F);
105    AssumptionCache *AC =
106        &getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
107    OptimizationRemarkEmitter *ORE =
108        &getAnalysis<OptimizationRemarkEmitterWrapperPass>().getORE();
109    const DataLayout &DL = F.getParent()->getDataLayout();
110    const SimplifyQuery SQ(DL, TLI, DT, AC);
111    return runImpl(F, SQ, ORE);
112  }
113};
114} // namespace
115
116char InstSimplifyLegacyPass::ID = 0;
117INITIALIZE_PASS_BEGIN(InstSimplifyLegacyPass, "instsimplify",
118                      "Remove redundant instructions", false, false)
119INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
120INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
121INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
122INITIALIZE_PASS_DEPENDENCY(OptimizationRemarkEmitterWrapperPass)
123INITIALIZE_PASS_END(InstSimplifyLegacyPass, "instsimplify",
124                    "Remove redundant instructions", false, false)
125
126// Public interface to the simplify instructions pass.
127FunctionPass *llvm::createInstSimplifyLegacyPass() {
128  return new InstSimplifyLegacyPass();
129}
130
131PreservedAnalyses InstSimplifyPass::run(Function &F,
132                                        FunctionAnalysisManager &AM) {
133  auto &DT = AM.getResult<DominatorTreeAnalysis>(F);
134  auto &TLI = AM.getResult<TargetLibraryAnalysis>(F);
135  auto &AC = AM.getResult<AssumptionAnalysis>(F);
136  auto &ORE = AM.getResult<OptimizationRemarkEmitterAnalysis>(F);
137  const DataLayout &DL = F.getParent()->getDataLayout();
138  const SimplifyQuery SQ(DL, &TLI, &DT, &AC);
139  bool Changed = runImpl(F, SQ, &ORE);
140  if (!Changed)
141    return PreservedAnalyses::all();
142
143  PreservedAnalyses PA;
144  PA.preserveSet<CFGAnalyses>();
145  return PA;
146}
147