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/Scalar.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 using namespace llvm;
31
32 #define DEBUG_TYPE "instsimplify"
33
34 STATISTIC(NumSimplified, "Number of redundant instructions removed");
35
36 namespace {
37 struct InstSimplifier : public FunctionPass {
38 static char ID; // Pass identification, replacement for typeid
InstSimplifier__anon567942320111::InstSimplifier39 InstSimplifier() : FunctionPass(ID) {
40 initializeInstSimplifierPass(*PassRegistry::getPassRegistry());
41 }
42
getAnalysisUsage__anon567942320111::InstSimplifier43 void getAnalysisUsage(AnalysisUsage &AU) const override {
44 AU.setPreservesCFG();
45 AU.addRequired<AssumptionCacheTracker>();
46 AU.addRequired<TargetLibraryInfoWrapperPass>();
47 }
48
49 /// runOnFunction - Remove instructions that simplify.
runOnFunction__anon567942320111::InstSimplifier50 bool runOnFunction(Function &F) override {
51 const DominatorTreeWrapperPass *DTWP =
52 getAnalysisIfAvailable<DominatorTreeWrapperPass>();
53 const DominatorTree *DT = DTWP ? &DTWP->getDomTree() : nullptr;
54 const DataLayout &DL = F.getParent()->getDataLayout();
55 const TargetLibraryInfo *TLI =
56 &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
57 AssumptionCache *AC =
58 &getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
59 SmallPtrSet<const Instruction*, 8> S1, S2, *ToSimplify = &S1, *Next = &S2;
60 bool Changed = false;
61
62 do {
63 for (BasicBlock *BB : depth_first(&F.getEntryBlock()))
64 // Here be subtlety: the iterator must be incremented before the loop
65 // body (not sure why), so a range-for loop won't work here.
66 for (BasicBlock::iterator BI = BB->begin(), BE = BB->end(); BI != BE;) {
67 Instruction *I = &*BI++;
68 // The first time through the loop ToSimplify is empty and we try to
69 // simplify all instructions. On later iterations ToSimplify is not
70 // empty and we only bother simplifying instructions that are in it.
71 if (!ToSimplify->empty() && !ToSimplify->count(I))
72 continue;
73 // Don't waste time simplifying unused instructions.
74 if (!I->use_empty())
75 if (Value *V = SimplifyInstruction(I, DL, TLI, DT, AC)) {
76 // Mark all uses for resimplification next time round the loop.
77 for (User *U : I->users())
78 Next->insert(cast<Instruction>(U));
79 I->replaceAllUsesWith(V);
80 ++NumSimplified;
81 Changed = true;
82 }
83 bool res = RecursivelyDeleteTriviallyDeadInstructions(I, TLI);
84 if (res) {
85 // RecursivelyDeleteTriviallyDeadInstruction can remove
86 // more than one instruction, so simply incrementing the
87 // iterator does not work. When instructions get deleted
88 // re-iterate instead.
89 BI = BB->begin(); BE = BB->end();
90 Changed |= res;
91 }
92 }
93
94 // Place the list of instructions to simplify on the next loop iteration
95 // into ToSimplify.
96 std::swap(ToSimplify, Next);
97 Next->clear();
98 } while (!ToSimplify->empty());
99
100 return Changed;
101 }
102 };
103 }
104
105 char InstSimplifier::ID = 0;
106 INITIALIZE_PASS_BEGIN(InstSimplifier, "instsimplify",
107 "Remove redundant instructions", false, false)
108 INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
109 INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
110 INITIALIZE_PASS_END(InstSimplifier, "instsimplify",
111 "Remove redundant instructions", false, false)
112 char &llvm::InstructionSimplifierID = InstSimplifier::ID;
113
114 // Public interface to the simplify instructions pass.
createInstructionSimplifierPass()115 FunctionPass *llvm::createInstructionSimplifierPass() {
116 return new InstSimplifier();
117 }
118