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/Function.h"
  19 #include "llvm/Pass.h"
  20 #include "llvm/Type.h"
  21 #include "llvm/ADT/DepthFirstIterator.h"
  22 #include "llvm/ADT/Statistic.h"
  23 #include "llvm/Analysis/Dominators.h"
  24 #include "llvm/Analysis/InstructionSimplify.h"
  25 #include "llvm/Target/TargetData.h"
  26 #include "llvm/Transforms/Scalar.h"
  27 #include "llvm/Transforms/Utils/Local.h"
  28 using namespace llvm;
  29
  30 STATISTIC(NumSimplified, "Number of redundant instructions removed");
  31
  32 namespace {
  33   struct InstSimplifier : public FunctionPass {
  34     static char ID; // Pass identification, replacement for typeid
  35     InstSimplifier() : FunctionPass(ID) {
  36       initializeInstSimplifierPass(*PassRegistry::getPassRegistry());
  37     }
  38
  39     void getAnalysisUsage(AnalysisUsage &AU) const {
  40       AU.setPreservesCFG();
  41     }
  42
  43     /// runOnFunction - Remove instructions that simplify.
  44     bool runOnFunction(Function &F) {
  45       const DominatorTree *DT = getAnalysisIfAvailable<DominatorTree>();
  46       const TargetData *TD = getAnalysisIfAvailable<TargetData>();
  47       bool Changed = false;
  48       bool LocalChanged;
  49
  50       do {
  51         LocalChanged = false;
  52
  53         for (df_iterator<BasicBlock*> DI = df_begin(&F.getEntryBlock()),
  54              DE = df_end(&F.getEntryBlock()); DI != DE; ++DI)
  55           for (BasicBlock::iterator BI = DI->begin(), BE = DI->end(); BI != BE;) {
  56             Instruction *I = BI++;
  57             // Don't bother simplifying unused instructions.
  58             if (!I->use_empty())
  59               if (Value *V = SimplifyInstruction(I, TD, DT)) {
  60                 I->replaceAllUsesWith(V);
  61                 LocalChanged = true;
  62                 ++NumSimplified;
  63               }
  64             LocalChanged |= RecursivelyDeleteTriviallyDeadInstructions(I);
  65           }
  66
  67         Changed |= LocalChanged;
  68       } while (LocalChanged);
  69
  70       return Changed;
  71     }
  72   };
  73 }
  74
  75 char InstSimplifier::ID = 0;
  76 INITIALIZE_PASS(InstSimplifier, "instsimplify", "Remove redundant instructions",
  77                 false, false)
  78 char &llvm::InstructionSimplifierID = InstSimplifier::ID;
  79
  80 // Public interface to the simplify instructions pass.
  81 FunctionPass *llvm::createInstructionSimplifierPass() {
  82   return new InstSimplifier();
  83 }