lib/Transforms/Scalar/CorrelatedValuePropagation.cpp

   1 //===- CorrelatedValuePropagation.cpp - Propagate CFG-derived info --------===//
   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 file implements the Correlated Value Propagation pass.
  11 //
  12 //===----------------------------------------------------------------------===//
  13
  14 #define DEBUG_TYPE "correlated-value-propagation"
  15 #include "llvm/Transforms/Scalar.h"
  16 #include "llvm/Function.h"
  17 #include "llvm/Instructions.h"
  18 #include "llvm/Pass.h"
  19 #include "llvm/Analysis/LazyValueInfo.h"
  20 #include "llvm/Transforms/Utils/Local.h"
  21 #include "llvm/ADT/Statistic.h"
  22 using namespace llvm;
  23
  24 STATISTIC(NumPhis,      "Number of phis propagated");
  25 STATISTIC(NumSelects,   "Number of selects propagated");
  26 STATISTIC(NumMemAccess, "Number of memory access targets propagated");
  27
  28 namespace {
  29   class CorrelatedValuePropagation : public FunctionPass {
  30     LazyValueInfo *LVI;
  31
  32     bool processSelect(SelectInst *SI);
  33     bool processPHI(PHINode *P);
  34     bool processMemAccess(Instruction *I);
  35
  36   public:
  37     static char ID;
  38     CorrelatedValuePropagation(): FunctionPass(ID) { }
  39
  40     bool runOnFunction(Function &F);
  41
  42     virtual void getAnalysisUsage(AnalysisUsage &AU) const {
  43       AU.addRequired<LazyValueInfo>();
  44     }
  45   };
  46 }
  47
  48 char CorrelatedValuePropagation::ID = 0;
  49 INITIALIZE_PASS(CorrelatedValuePropagation, "correlated-propagation",
  50                 "Value Propagation", false, false);
  51
  52 // Public interface to the Value Propagation pass
  53 Pass *llvm::createCorrelatedValuePropagationPass() {
  54   return new CorrelatedValuePropagation();
  55 }
  56
  57 bool CorrelatedValuePropagation::processSelect(SelectInst *S) {
  58   if (S->getType()->isVectorTy()) return false;
  59   if (isa<Constant>(S->getOperand(0))) return false;
  60
  61   Constant *C = LVI->getConstant(S->getOperand(0), S->getParent());
  62   if (!C) return false;
  63
  64   ConstantInt *CI = dyn_cast<ConstantInt>(C);
  65   if (!CI) return false;
  66
  67   S->replaceAllUsesWith(S->getOperand(CI->isOne() ? 1 : 2));
  68   S->eraseFromParent();
  69
  70   ++NumSelects;
  71
  72   return true;
  73 }
  74
  75 bool CorrelatedValuePropagation::processPHI(PHINode *P) {
  76   bool Changed = false;
  77
  78   BasicBlock *BB = P->getParent();
  79   for (unsigned i = 0, e = P->getNumIncomingValues(); i < e; ++i) {
  80     Value *Incoming = P->getIncomingValue(i);
  81     if (isa<Constant>(Incoming)) continue;
  82
  83     Constant *C = LVI->getConstantOnEdge(P->getIncomingValue(i),
  84                                          P->getIncomingBlock(i),
  85                                          BB);
  86     if (!C) continue;
  87
  88     P->setIncomingValue(i, C);
  89     Changed = true;
  90   }
  91
  92   if (Value *ConstVal = P->hasConstantValue()) {
  93     P->replaceAllUsesWith(ConstVal);
  94     P->eraseFromParent();
  95     Changed = true;
  96   }
  97
  98   ++NumPhis;
  99
 100   return Changed;
 101 }
 102
 103 bool CorrelatedValuePropagation::processMemAccess(Instruction *I) {
 104   Value *Pointer = 0;
 105   if (LoadInst *L = dyn_cast<LoadInst>(I))
 106     Pointer = L->getPointerOperand();
 107   else
 108     Pointer = cast<StoreInst>(I)->getPointerOperand();
 109
 110   if (isa<Constant>(Pointer)) return false;
 111
 112   Constant *C = LVI->getConstant(Pointer, I->getParent());
 113   if (!C) return false;
 114
 115   ++NumMemAccess;
 116   I->replaceUsesOfWith(Pointer, C);
 117   return true;
 118 }
 119
 120 bool CorrelatedValuePropagation::runOnFunction(Function &F) {
 121   LVI = &getAnalysis<LazyValueInfo>();
 122
 123   bool FnChanged = false;
 124
 125   for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ++FI) {
 126     bool BBChanged = false;
 127     for (BasicBlock::iterator BI = FI->begin(), BE = FI->end(); BI != BE; ) {
 128       Instruction *II = BI++;
 129       switch (II->getOpcode()) {
 130       case Instruction::Select:
 131         BBChanged |= processSelect(cast<SelectInst>(II));
 132         break;
 133       case Instruction::PHI:
 134         BBChanged |= processPHI(cast<PHINode>(II));
 135         break;
 136       case Instruction::Load:
 137       case Instruction::Store:
 138         BBChanged |= processMemAccess(II);
 139         break;
 140       }
 141     }
 142
 143     // Propagating correlated values might leave cruft around.
 144     // Try to clean it up before we continue.
 145     if (BBChanged)
 146       SimplifyInstructionsInBlock(FI);
 147
 148     FnChanged |= BBChanged;
 149   }
 150
 151   return FnChanged;
 152 }