1 //===------ SimplifyInstructions.cpp - Remove redundant instructions ------===//
2 //
3 // The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // This is a utility pass used for testing the InstructionSimplify analysis.
11 // The analysis is applied to every instruction, and if it simplifies then the
12 // instruction is replaced by the simplification. If you are looking for a pass
13 // that performs serious instruction folding, use the instcombine pass instead.
14 //
15 //===----------------------------------------------------------------------===//
16
17 #include "llvm/Transforms/Utils/SimplifyInstructions.h"
18 #include "llvm/ADT/DepthFirstIterator.h"
19 #include "llvm/ADT/SmallPtrSet.h"
20 #include "llvm/ADT/Statistic.h"
21 #include "llvm/Analysis/AssumptionCache.h"
22 #include "llvm/Analysis/InstructionSimplify.h"
23 #include "llvm/Analysis/TargetLibraryInfo.h"
24 #include "llvm/IR/DataLayout.h"
25 #include "llvm/IR/Dominators.h"
26 #include "llvm/IR/Function.h"
27 #include "llvm/IR/Type.h"
28 #include "llvm/Pass.h"
29 #include "llvm/Transforms/Utils/Local.h"
30 #include "llvm/Transforms/Scalar.h"
31 using namespace llvm;
32
33 #define DEBUG_TYPE "instsimplify"
34
35 STATISTIC(NumSimplified, "Number of redundant instructions removed");
36
runImpl(Function & F,const DominatorTree * DT,const TargetLibraryInfo * TLI,AssumptionCache * AC)37 static bool runImpl(Function &F, const DominatorTree *DT, const TargetLibraryInfo *TLI,
38 AssumptionCache *AC) {
39 const DataLayout &DL = F.getParent()->getDataLayout();
40 SmallPtrSet<const Instruction*, 8> S1, S2, *ToSimplify = &S1, *Next = &S2;
41 bool Changed = false;
42
43 do {
44 for (BasicBlock *BB : depth_first(&F.getEntryBlock()))
45 // Here be subtlety: the iterator must be incremented before the loop
46 // body (not sure why), so a range-for loop won't work here.
47 for (BasicBlock::iterator BI = BB->begin(), BE = BB->end(); BI != BE;) {
48 Instruction *I = &*BI++;
49 // The first time through the loop ToSimplify is empty and we try to
50 // simplify all instructions. On later iterations ToSimplify is not
51 // empty and we only bother simplifying instructions that are in it.
52 if (!ToSimplify->empty() && !ToSimplify->count(I))
53 continue;
54 // Don't waste time simplifying unused instructions.
55 if (!I->use_empty())
56 if (Value *V = SimplifyInstruction(I, DL, TLI, DT, AC)) {
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 }
64 bool res = RecursivelyDeleteTriviallyDeadInstructions(I, TLI);
65 if (res) {
66 // RecursivelyDeleteTriviallyDeadInstruction can remove
67 // more than one instruction, so simply incrementing the
68 // iterator does not work. When instructions get deleted
69 // re-iterate instead.
70 BI = BB->begin(); BE = BB->end();
71 Changed |= res;
72 }
73 }
74
75 // Place the list of instructions to simplify on the next loop iteration
76 // into ToSimplify.
77 std::swap(ToSimplify, Next);
78 Next->clear();
79 } while (!ToSimplify->empty());
80
81 return Changed;
82 }
83
84 namespace {
85 struct InstSimplifier : public FunctionPass {
86 static char ID; // Pass identification, replacement for typeid
InstSimplifier__anon41ea2fdb0111::InstSimplifier87 InstSimplifier() : FunctionPass(ID) {
88 initializeInstSimplifierPass(*PassRegistry::getPassRegistry());
89 }
90
getAnalysisUsage__anon41ea2fdb0111::InstSimplifier91 void getAnalysisUsage(AnalysisUsage &AU) const override {
92 AU.setPreservesCFG();
93 AU.addRequired<AssumptionCacheTracker>();
94 AU.addRequired<TargetLibraryInfoWrapperPass>();
95 }
96
97 /// runOnFunction - Remove instructions that simplify.
runOnFunction__anon41ea2fdb0111::InstSimplifier98 bool runOnFunction(Function &F) override {
99 if (skipFunction(F))
100 return false;
101
102 const DominatorTreeWrapperPass *DTWP =
103 getAnalysisIfAvailable<DominatorTreeWrapperPass>();
104 const DominatorTree *DT = DTWP ? &DTWP->getDomTree() : nullptr;
105 const TargetLibraryInfo *TLI =
106 &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
107 AssumptionCache *AC =
108 &getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
109 return runImpl(F, DT, TLI, AC);
110 }
111 };
112 }
113
114 char InstSimplifier::ID = 0;
115 INITIALIZE_PASS_BEGIN(InstSimplifier, "instsimplify",
116 "Remove redundant instructions", false, false)
117 INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
118 INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
119 INITIALIZE_PASS_END(InstSimplifier, "instsimplify",
120 "Remove redundant instructions", false, false)
121 char &llvm::InstructionSimplifierID = InstSimplifier::ID;
122
123 // Public interface to the simplify instructions pass.
createInstructionSimplifierPass()124 FunctionPass *llvm::createInstructionSimplifierPass() {
125 return new InstSimplifier();
126 }
127
run(Function & F,AnalysisManager<Function> & AM)128 PreservedAnalyses InstSimplifierPass::run(Function &F,
129 AnalysisManager<Function> &AM) {
130 auto *DT = AM.getCachedResult<DominatorTreeAnalysis>(F);
131 auto &TLI = AM.getResult<TargetLibraryAnalysis>(F);
132 auto &AC = AM.getResult<AssumptionAnalysis>(F);
133 bool Changed = runImpl(F, DT, &TLI, &AC);
134 if (!Changed)
135 return PreservedAnalyses::all();
136 // FIXME: This should also 'preserve the CFG'.
137 return PreservedAnalyses::none();
138 }
139