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/Constants.h"
  17 #include "llvm/Function.h"
  18 #include "llvm/Instructions.h"
  19 #include "llvm/Pass.h"
  20 #include "llvm/Analysis/InstructionSimplify.h"
  21 #include "llvm/Analysis/LazyValueInfo.h"
  22 #include "llvm/Support/CFG.h"
  23 #include "llvm/Transforms/Utils/Local.h"
  24 #include "llvm/ADT/Statistic.h"
  25 using namespace llvm;
  26
  27 STATISTIC(NumPhis,      "Number of phis propagated");
  28 STATISTIC(NumSelects,   "Number of selects propagated");
  29 STATISTIC(NumMemAccess, "Number of memory access targets propagated");
  30 STATISTIC(NumCmps,      "Number of comparisons propagated");
  31
  32 namespace {
  33   class CorrelatedValuePropagation : public FunctionPass {
  34     LazyValueInfo *LVI;
  35
  36     bool processSelect(SelectInst *SI);
  37     bool processPHI(PHINode *P);
  38     bool processMemAccess(Instruction *I);
  39     bool processCmp(CmpInst *C);
  40
  41   public:
  42     static char ID;
  43     CorrelatedValuePropagation(): FunctionPass(ID) {
  44      initializeCorrelatedValuePropagationPass(*PassRegistry::getPassRegistry());
  45     }
  46
  47     bool runOnFunction(Function &F);
  48
  49     virtual void getAnalysisUsage(AnalysisUsage &AU) const {
  50       AU.addRequired<LazyValueInfo>();
  51     }
  52   };
  53 }
  54
  55 char CorrelatedValuePropagation::ID = 0;
  56 INITIALIZE_PASS_BEGIN(CorrelatedValuePropagation, "correlated-propagation",
  57                 "Value Propagation", false, false)
  58 INITIALIZE_PASS_DEPENDENCY(LazyValueInfo)
  59 INITIALIZE_PASS_END(CorrelatedValuePropagation, "correlated-propagation",
  60                 "Value Propagation", false, false)
  61
  62 // Public interface to the Value Propagation pass
  63 Pass *llvm::createCorrelatedValuePropagationPass() {
  64   return new CorrelatedValuePropagation();
  65 }
  66
  67 bool CorrelatedValuePropagation::processSelect(SelectInst *S) {
  68   if (S->getType()->isVectorTy()) return false;
  69   if (isa<Constant>(S->getOperand(0))) return false;
  70
  71   Constant *C = LVI->getConstant(S->getOperand(0), S->getParent());
  72   if (!C) return false;
  73
  74   ConstantInt *CI = dyn_cast<ConstantInt>(C);
  75   if (!CI) return false;
  76
  77   Value *ReplaceWith = S->getOperand(1);
  78   Value *Other = S->getOperand(2);
  79   if (!CI->isOne()) std::swap(ReplaceWith, Other);
  80   if (ReplaceWith == S) ReplaceWith = UndefValue::get(S->getType());
  81
  82   S->replaceAllUsesWith(ReplaceWith);
  83   S->eraseFromParent();
  84
  85   ++NumSelects;
  86
  87   return true;
  88 }
  89
  90 bool CorrelatedValuePropagation::processPHI(PHINode *P) {
  91   bool Changed = false;
  92
  93   BasicBlock *BB = P->getParent();
  94   for (unsigned i = 0, e = P->getNumIncomingValues(); i < e; ++i) {
  95     Value *Incoming = P->getIncomingValue(i);
  96     if (isa<Constant>(Incoming)) continue;
  97
  98     Constant *C = LVI->getConstantOnEdge(P->getIncomingValue(i),
  99                                          P->getIncomingBlock(i),
 100                                          BB);
 101     if (!C) continue;
 102
 103     P->setIncomingValue(i, C);
 104     Changed = true;
 105   }
 106
 107   if (Value *V = SimplifyInstruction(P)) {
 108     P->replaceAllUsesWith(V);
 109     P->eraseFromParent();
 110     Changed = true;
 111   }
 112
 113   ++NumPhis;
 114
 115   return Changed;
 116 }
 117
 118 bool CorrelatedValuePropagation::processMemAccess(Instruction *I) {
 119   Value *Pointer = 0;
 120   if (LoadInst *L = dyn_cast<LoadInst>(I))
 121     Pointer = L->getPointerOperand();
 122   else
 123     Pointer = cast<StoreInst>(I)->getPointerOperand();
 124
 125   if (isa<Constant>(Pointer)) return false;
 126
 127   Constant *C = LVI->getConstant(Pointer, I->getParent());
 128   if (!C) return false;
 129
 130   ++NumMemAccess;
 131   I->replaceUsesOfWith(Pointer, C);
 132   return true;
 133 }
 134
 135 /// processCmp - If the value of this comparison could be determined locally,
 136 /// constant propagation would already have figured it out.  Instead, walk
 137 /// the predecessors and statically evaluate the comparison based on information
 138 /// available on that edge.  If a given static evaluation is true on ALL
 139 /// incoming edges, then it's true universally and we can simplify the compare.
 140 bool CorrelatedValuePropagation::processCmp(CmpInst *C) {
 141   Value *Op0 = C->getOperand(0);
 142   if (isa<Instruction>(Op0) &&
 143       cast<Instruction>(Op0)->getParent() == C->getParent())
 144     return false;
 145
 146   Constant *Op1 = dyn_cast<Constant>(C->getOperand(1));
 147   if (!Op1) return false;
 148
 149   pred_iterator PI = pred_begin(C->getParent()), PE = pred_end(C->getParent());
 150   if (PI == PE) return false;
 151
 152   LazyValueInfo::Tristate Result = LVI->getPredicateOnEdge(C->getPredicate(),
 153                                     C->getOperand(0), Op1, *PI, C->getParent());
 154   if (Result == LazyValueInfo::Unknown) return false;
 155
 156   ++PI;
 157   while (PI != PE) {
 158     LazyValueInfo::Tristate Res = LVI->getPredicateOnEdge(C->getPredicate(),
 159                                     C->getOperand(0), Op1, *PI, C->getParent());
 160     if (Res != Result) return false;
 161     ++PI;
 162   }
 163
 164   ++NumCmps;
 165
 166   if (Result == LazyValueInfo::True)
 167     C->replaceAllUsesWith(ConstantInt::getTrue(C->getContext()));
 168   else
 169     C->replaceAllUsesWith(ConstantInt::getFalse(C->getContext()));
 170
 171   C->eraseFromParent();
 172
 173   return true;
 174 }
 175
 176 bool CorrelatedValuePropagation::runOnFunction(Function &F) {
 177   LVI = &getAnalysis<LazyValueInfo>();
 178
 179   bool FnChanged = false;
 180
 181   for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ++FI) {
 182     bool BBChanged = false;
 183     for (BasicBlock::iterator BI = FI->begin(), BE = FI->end(); BI != BE; ) {
 184       Instruction *II = BI++;
 185       switch (II->getOpcode()) {
 186       case Instruction::Select:
 187         BBChanged |= processSelect(cast<SelectInst>(II));
 188         break;
 189       case Instruction::PHI:
 190         BBChanged |= processPHI(cast<PHINode>(II));
 191         break;
 192       case Instruction::ICmp:
 193       case Instruction::FCmp:
 194         BBChanged |= processCmp(cast<CmpInst>(II));
 195         break;
 196       case Instruction::Load:
 197       case Instruction::Store:
 198         BBChanged |= processMemAccess(II);
 199         break;
 200       }
 201     }
 202
 203     FnChanged |= BBChanged;
 204   }
 205
 206   return FnChanged;
 207 }