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