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/InstructionSimplify.h"
  20 #include "llvm/Analysis/LazyValueInfo.h"
  21 #include "llvm/Support/CFG.h"
  22 #include "llvm/Transforms/Utils/Local.h"
  23 #include "llvm/ADT/Statistic.h"
  24 using namespace llvm;
  25
  26 STATISTIC(NumPhis,      "Number of phis propagated");
  27 STATISTIC(NumSelects,   "Number of selects propagated");
  28 STATISTIC(NumMemAccess, "Number of memory access targets propagated");
  29 STATISTIC(NumCmps,      "Number of comparisons propagated");
  30
  31 namespace {
  32   class CorrelatedValuePropagation : public FunctionPass {
  33     LazyValueInfo *LVI;
  34
  35     bool processSelect(SelectInst *SI);
  36     bool processPHI(PHINode *P);
  37     bool processMemAccess(Instruction *I);
  38     bool processCmp(CmpInst *C);
  39
  40   public:
  41     static char ID;
  42     CorrelatedValuePropagation(): FunctionPass(ID) {
  43      initializeCorrelatedValuePropagationPass(*PassRegistry::getPassRegistry());
  44     }
  45
  46     bool runOnFunction(Function &F);
  47
  48     virtual void getAnalysisUsage(AnalysisUsage &AU) const {
  49       AU.addRequired<LazyValueInfo>();
  50     }
  51   };
  52 }
  53
  54 char CorrelatedValuePropagation::ID = 0;
  55 INITIALIZE_PASS_BEGIN(CorrelatedValuePropagation, "correlated-propagation",
  56                 "Value Propagation", false, false)
  57 INITIALIZE_PASS_DEPENDENCY(LazyValueInfo)
  58 INITIALIZE_PASS_END(CorrelatedValuePropagation, "correlated-propagation",
  59                 "Value Propagation", false, false)
  60
  61 // Public interface to the Value Propagation pass
  62 Pass *llvm::createCorrelatedValuePropagationPass() {
  63   return new CorrelatedValuePropagation();
  64 }
  65
  66 bool CorrelatedValuePropagation::processSelect(SelectInst *S) {
  67   if (S->getType()->isVectorTy()) return false;
  68   if (isa<Constant>(S->getOperand(0))) return false;
  69
  70   Constant *C = LVI->getConstant(S->getOperand(0), S->getParent());
  71   if (!C) return false;
  72
  73   ConstantInt *CI = dyn_cast<ConstantInt>(C);
  74   if (!CI) return false;
  75
  76   Value *ReplaceWith = S->getOperand(1);
  77   Value *Other = S->getOperand(2);
  78   if (!CI->isOne()) std::swap(ReplaceWith, Other);
  79   if (ReplaceWith == S) ReplaceWith = UndefValue::get(S->getType());
  80
  81   S->replaceAllUsesWith(ReplaceWith);
  82   S->eraseFromParent();
  83
  84   ++NumSelects;
  85
  86   return true;
  87 }
  88
  89 bool CorrelatedValuePropagation::processPHI(PHINode *P) {
  90   bool Changed = false;
  91
  92   BasicBlock *BB = P->getParent();
  93   for (unsigned i = 0, e = P->getNumIncomingValues(); i < e; ++i) {
  94     Value *Incoming = P->getIncomingValue(i);
  95     if (isa<Constant>(Incoming)) continue;
  96
  97     Constant *C = LVI->getConstantOnEdge(P->getIncomingValue(i),
  98                                          P->getIncomingBlock(i),
  99                                          BB);
 100     if (!C) continue;
 101
 102     P->setIncomingValue(i, C);
 103     Changed = true;
 104   }
 105
 106   if (Value *V = SimplifyInstruction(P)) {
 107     P->replaceAllUsesWith(V);
 108     P->eraseFromParent();
 109     Changed = true;
 110   }
 111
 112   ++NumPhis;
 113
 114   return Changed;
 115 }
 116
 117 bool CorrelatedValuePropagation::processMemAccess(Instruction *I) {
 118   Value *Pointer = 0;
 119   if (LoadInst *L = dyn_cast<LoadInst>(I))
 120     Pointer = L->getPointerOperand();
 121   else
 122     Pointer = cast<StoreInst>(I)->getPointerOperand();
 123
 124   if (isa<Constant>(Pointer)) return false;
 125
 126   Constant *C = LVI->getConstant(Pointer, I->getParent());
 127   if (!C) return false;
 128
 129   ++NumMemAccess;
 130   I->replaceUsesOfWith(Pointer, C);
 131   return true;
 132 }
 133
 134 /// processCmp - If the value of this comparison could be determined locally,
 135 /// constant propagation would already have figured it out.  Instead, walk
 136 /// the predecessors and statically evaluate the comparison based on information
 137 /// available on that edge.  If a given static evaluation is true on ALL
 138 /// incoming edges, then it's true universally and we can simplify the compare.
 139 bool CorrelatedValuePropagation::processCmp(CmpInst *C) {
 140   Value *Op0 = C->getOperand(0);
 141   if (isa<Instruction>(Op0) &&
 142       cast<Instruction>(Op0)->getParent() == C->getParent())
 143     return false;
 144
 145   Constant *Op1 = dyn_cast<Constant>(C->getOperand(1));
 146   if (!Op1) return false;
 147
 148   pred_iterator PI = pred_begin(C->getParent()), PE = pred_end(C->getParent());
 149   if (PI == PE) return false;
 150
 151   LazyValueInfo::Tristate Result = LVI->getPredicateOnEdge(C->getPredicate(),
 152                                     C->getOperand(0), Op1, *PI, C->getParent());
 153   if (Result == LazyValueInfo::Unknown) return false;
 154
 155   ++PI;
 156   while (PI != PE) {
 157     LazyValueInfo::Tristate Res = LVI->getPredicateOnEdge(C->getPredicate(),
 158                                     C->getOperand(0), Op1, *PI, C->getParent());
 159     if (Res != Result) return false;
 160     ++PI;
 161   }
 162
 163   ++NumCmps;
 164
 165   if (Result == LazyValueInfo::True)
 166     C->replaceAllUsesWith(ConstantInt::getTrue(C->getContext()));
 167   else
 168     C->replaceAllUsesWith(ConstantInt::getFalse(C->getContext()));
 169
 170   C->eraseFromParent();
 171
 172   return true;
 173 }
 174
 175 bool CorrelatedValuePropagation::runOnFunction(Function &F) {
 176   LVI = &getAnalysis<LazyValueInfo>();
 177
 178   bool FnChanged = false;
 179
 180   for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ++FI) {
 181     bool BBChanged = false;
 182     for (BasicBlock::iterator BI = FI->begin(), BE = FI->end(); BI != BE; ) {
 183       Instruction *II = BI++;
 184       switch (II->getOpcode()) {
 185       case Instruction::Select:
 186         BBChanged |= processSelect(cast<SelectInst>(II));
 187         break;
 188       case Instruction::PHI:
 189         BBChanged |= processPHI(cast<PHINode>(II));
 190         break;
 191       case Instruction::ICmp:
 192       case Instruction::FCmp:
 193         BBChanged |= processCmp(cast<CmpInst>(II));
 194         break;
 195       case Instruction::Load:
 196       case Instruction::Store:
 197         BBChanged |= processMemAccess(II);
 198         break;
 199       }
 200     }
 201
 202     FnChanged |= BBChanged;
 203   }
 204
 205   return FnChanged;
 206 }