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