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