lib/Transforms/Utils/SimplifyInstructions.cpp

   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 #define DEBUG_TYPE "instsimplify"
  18 #include "llvm/Transforms/Scalar.h"
  19 #include "llvm/ADT/DepthFirstIterator.h"
  20 #include "llvm/ADT/SmallPtrSet.h"
  21 #include "llvm/ADT/Statistic.h"
  22 #include "llvm/Analysis/InstructionSimplify.h"
  23 #include "llvm/IR/DataLayout.h"
  24 #include "llvm/IR/Dominators.h"
  25 #include "llvm/IR/Function.h"
  26 #include "llvm/IR/Type.h"
  27 #include "llvm/Pass.h"
  28 #include "llvm/Target/TargetLibraryInfo.h"
  29 #include "llvm/Transforms/Utils/Local.h"
  30 using namespace llvm;
  31
  32 STATISTIC(NumSimplified, "Number of redundant instructions removed");
  33
  34 namespace {
  35   struct InstSimplifier : public FunctionPass {
  36     static char ID; // Pass identification, replacement for typeid
  37     InstSimplifier() : FunctionPass(ID) {
  38       initializeInstSimplifierPass(*PassRegistry::getPassRegistry());
  39     }
  40
  41     void getAnalysisUsage(AnalysisUsage &AU) const {
  42       AU.setPreservesCFG();
  43       AU.addRequired<TargetLibraryInfo>();
  44     }
  45
  46     /// runOnFunction - Remove instructions that simplify.
  47     bool runOnFunction(Function &F) {
  48       const DominatorTree *DT = getAnalysisIfAvailable<DominatorTree>();
  49       const DataLayout *TD = getAnalysisIfAvailable<DataLayout>();
  50       const TargetLibraryInfo *TLI = &getAnalysis<TargetLibraryInfo>();
  51       SmallPtrSet<const Instruction*, 8> S1, S2, *ToSimplify = &S1, *Next = &S2;
  52       bool Changed = false;
  53
  54       do {
  55         for (df_iterator<BasicBlock*> DI = df_begin(&F.getEntryBlock()),
  56              DE = df_end(&F.getEntryBlock()); DI != DE; ++DI)
  57           for (BasicBlock::iterator BI = DI->begin(), BE = DI->end(); BI != BE;) {
  58             Instruction *I = BI++;
  59             // The first time through the loop ToSimplify is empty and we try to
  60             // simplify all instructions.  On later iterations ToSimplify is not
  61             // empty and we only bother simplifying instructions that are in it.
  62             if (!ToSimplify->empty() && !ToSimplify->count(I))
  63               continue;
  64             // Don't waste time simplifying unused instructions.
  65             if (!I->use_empty())
  66               if (Value *V = SimplifyInstruction(I, TD, TLI, DT)) {
  67                 // Mark all uses for resimplification next time round the loop.
  68                 for (Value::use_iterator UI = I->use_begin(), UE = I->use_end();
  69                      UI != UE; ++UI)
  70                   Next->insert(cast<Instruction>(*UI));
  71                 I->replaceAllUsesWith(V);
  72                 ++NumSimplified;
  73                 Changed = true;
  74               }
  75             Changed |= RecursivelyDeleteTriviallyDeadInstructions(I, TLI);
  76           }
  77
  78         // Place the list of instructions to simplify on the next loop iteration
  79         // into ToSimplify.
  80         std::swap(ToSimplify, Next);
  81         Next->clear();
  82       } while (!ToSimplify->empty());
  83
  84       return Changed;
  85     }
  86   };
  87 }
  88
  89 char InstSimplifier::ID = 0;
  90 INITIALIZE_PASS_BEGIN(InstSimplifier, "instsimplify",
  91                       "Remove redundant instructions", false, false)
  92 INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfo)
  93 INITIALIZE_PASS_END(InstSimplifier, "instsimplify",
  94                     "Remove redundant instructions", false, false)
  95 char &llvm::InstructionSimplifierID = InstSimplifier::ID;
  96
  97 // Public interface to the simplify instructions pass.
  98 FunctionPass *llvm::createInstructionSimplifierPass() {
  99   return new InstSimplifier();
 100 }