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