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/Support/CFG.h"
  21 #include "llvm/Transforms/Utils/Local.h"
  22 #include "llvm/ADT/Statistic.h"
  23 using namespace llvm;
  24
  25 STATISTIC(NumPhis,      "Number of phis propagated");
  26 STATISTIC(NumSelects,   "Number of selects propagated");
  27 STATISTIC(NumMemAccess, "Number of memory access targets propagated");
  28 STATISTIC(NumCmps,      "Number of comparisons propagated");
  29
  30 namespace {
  31   class CorrelatedValuePropagation : public FunctionPass {
  32     LazyValueInfo *LVI;
  33
  34     bool processSelect(SelectInst *SI);
  35     bool processPHI(PHINode *P);
  36     bool processMemAccess(Instruction *I);
  37     bool processCmp(CmpInst *C);
  38
  39   public:
  40     static char ID;
  41     CorrelatedValuePropagation(): FunctionPass(ID) {
  42      initializeCorrelatedValuePropagationPass(*PassRegistry::getPassRegistry());
  43     }
  44
  45     bool runOnFunction(Function &F);
  46
  47     virtual void getAnalysisUsage(AnalysisUsage &AU) const {
  48       AU.addRequired<LazyValueInfo>();
  49     }
  50   };
  51 }
  52
  53 char CorrelatedValuePropagation::ID = 0;
  54 INITIALIZE_PASS_BEGIN(CorrelatedValuePropagation, "correlated-propagation",
  55                 "Value Propagation", false, false)
  56 INITIALIZE_PASS_DEPENDENCY(LazyValueInfo)
  57 INITIALIZE_PASS_END(CorrelatedValuePropagation, "correlated-propagation",
  58                 "Value Propagation", false, false)
  59
  60 // Public interface to the Value Propagation pass
  61 Pass *llvm::createCorrelatedValuePropagationPass() {
  62   return new CorrelatedValuePropagation();
  63 }
  64
  65 bool CorrelatedValuePropagation::processSelect(SelectInst *S) {
  66   if (S->getType()->isVectorTy()) return false;
  67   if (isa<Constant>(S->getOperand(0))) return false;
  68
  69   Constant *C = LVI->getConstant(S->getOperand(0), S->getParent());
  70   if (!C) return false;
  71
  72   ConstantInt *CI = dyn_cast<ConstantInt>(C);
  73   if (!CI) return false;
  74
  75   S->replaceAllUsesWith(S->getOperand(CI->isOne() ? 1 : 2));
  76   S->eraseFromParent();
  77
  78   ++NumSelects;
  79
  80   return true;
  81 }
  82
  83 bool CorrelatedValuePropagation::processPHI(PHINode *P) {
  84   bool Changed = false;
  85
  86   BasicBlock *BB = P->getParent();
  87   for (unsigned i = 0, e = P->getNumIncomingValues(); i < e; ++i) {
  88     Value *Incoming = P->getIncomingValue(i);
  89     if (isa<Constant>(Incoming)) continue;
  90
  91     Constant *C = LVI->getConstantOnEdge(P->getIncomingValue(i),
  92                                          P->getIncomingBlock(i),
  93                                          BB);
  94     if (!C) continue;
  95
  96     P->setIncomingValue(i, C);
  97     Changed = true;
  98   }
  99
 100   if (Value *ConstVal = P->hasConstantValue()) {
 101     P->replaceAllUsesWith(ConstVal);
 102     P->eraseFromParent();
 103     Changed = true;
 104   }
 105
 106   ++NumPhis;
 107
 108   return Changed;
 109 }
 110
 111 bool CorrelatedValuePropagation::processMemAccess(Instruction *I) {
 112   Value *Pointer = 0;
 113   if (LoadInst *L = dyn_cast<LoadInst>(I))
 114     Pointer = L->getPointerOperand();
 115   else
 116     Pointer = cast<StoreInst>(I)->getPointerOperand();
 117
 118   if (isa<Constant>(Pointer)) return false;
 119
 120   Constant *C = LVI->getConstant(Pointer, I->getParent());
 121   if (!C) return false;
 122
 123   ++NumMemAccess;
 124   I->replaceUsesOfWith(Pointer, C);
 125   return true;
 126 }
 127
 128 /// processCmp - If the value of this comparison could be determined locally,
 129 /// constant propagation would already have figured it out.  Instead, walk
 130 /// the predecessors and statically evaluate the comparison based on information
 131 /// available on that edge.  If a given static evaluation is true on ALL
 132 /// incoming edges, then it's true universally and we can simplify the compare.
 133 bool CorrelatedValuePropagation::processCmp(CmpInst *C) {
 134   Value *Op0 = C->getOperand(0);
 135   if (isa<Instruction>(Op0) &&
 136       cast<Instruction>(Op0)->getParent() == C->getParent())
 137     return false;
 138
 139   Constant *Op1 = dyn_cast<Constant>(C->getOperand(1));
 140   if (!Op1) return false;
 141
 142   pred_iterator PI = pred_begin(C->getParent()), PE = pred_end(C->getParent());
 143   if (PI == PE) return false;
 144
 145   LazyValueInfo::Tristate Result = LVI->getPredicateOnEdge(C->getPredicate(),
 146                                     C->getOperand(0), Op1, *PI, C->getParent());
 147   if (Result == LazyValueInfo::Unknown) return false;
 148
 149   ++PI;
 150   while (PI != PE) {
 151     LazyValueInfo::Tristate Res = LVI->getPredicateOnEdge(C->getPredicate(),
 152                                     C->getOperand(0), Op1, *PI, C->getParent());
 153     if (Res != Result) return false;
 154     ++PI;
 155   }
 156
 157   ++NumCmps;
 158
 159   if (Result == LazyValueInfo::True)
 160     C->replaceAllUsesWith(ConstantInt::getTrue(C->getContext()));
 161   else
 162     C->replaceAllUsesWith(ConstantInt::getFalse(C->getContext()));
 163
 164   C->eraseFromParent();
 165
 166   return true;
 167 }
 168
 169 bool CorrelatedValuePropagation::runOnFunction(Function &F) {
 170   LVI = &getAnalysis<LazyValueInfo>();
 171
 172   bool FnChanged = false;
 173
 174   for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ++FI) {
 175     bool BBChanged = false;
 176     for (BasicBlock::iterator BI = FI->begin(), BE = FI->end(); BI != BE; ) {
 177       Instruction *II = BI++;
 178       switch (II->getOpcode()) {
 179       case Instruction::Select:
 180         BBChanged |= processSelect(cast<SelectInst>(II));
 181         break;
 182       case Instruction::PHI:
 183         BBChanged |= processPHI(cast<PHINode>(II));
 184         break;
 185       case Instruction::ICmp:
 186       case Instruction::FCmp:
 187         BBChanged |= processCmp(cast<CmpInst>(II));
 188         break;
 189       case Instruction::Load:
 190       case Instruction::Store:
 191         BBChanged |= processMemAccess(II);
 192         break;
 193       }
 194     }
 195
 196     FnChanged |= BBChanged;
 197   }
 198
 199   return FnChanged;
 200 }