Constant propagation after hiting llvm.assume

[oota-llvm.git] / lib / Transforms / Scalar / GVN.cpp

diff --git a/lib/Transforms/Scalar/GVN.cpp b/lib/Transforms/Scalar/GVN.cpp
index d898b1796b6942ff6c9d0ac4b961c5942c244ef9..529524b0fe564ded50034a6eabcf89bdeb0916b4 100644 (file)
--- a/lib/Transforms/Scalar/GVN.cpp
+++ b/lib/Transforms/Scalar/GVN.cpp
@@ -608,6 +608,10 @@ namespace {
     DenseMap<uint32_t, LeaderTableEntry> LeaderTable;
     BumpPtrAllocator TableAllocator;
 
+    // Block-local map of equivalent values to their leader, does not
+    // propagate to any successors. Entries added mid-block are applied
+    // to the remaining instructions in the block.
+    SmallMapVector<llvm::Value *, llvm::Constant *, 4> ReplaceWithConstMap;
     SmallVector<Instruction*, 8> InstrsToErase;
 
     typedef SmallVector<NonLocalDepResult, 64> LoadDepVect;
@@ -699,6 +703,7 @@ namespace {
     // Helper functions of redundant load elimination 
     bool processLoad(LoadInst *L);
     bool processNonLocalLoad(LoadInst *L);
+    bool processAssumeIntrinsic(IntrinsicInst *II);
     void AnalyzeLoadAvailability(LoadInst *LI, LoadDepVect &Deps, 
                                  AvailValInBlkVect &ValuesPerBlock,
                                  UnavailBlkVect &UnavailableBlocks);
@@ -719,6 +724,7 @@ namespace {
     void verifyRemoved(const Instruction *I) const;
     bool splitCriticalEdges();
     BasicBlock *splitCriticalEdges(BasicBlock *Pred, BasicBlock *Succ);
+    bool replaceOperandsWithConsts(Instruction *I) const;
     bool propagateEquality(Value *LHS, Value *RHS, const BasicBlockEdge &Root);
     bool processFoldableCondBr(BranchInst *BI);
     void addDeadBlock(BasicBlock *BB);
@@ -1760,6 +1766,38 @@ bool GVN::processNonLocalLoad(LoadInst *LI) {
   return PerformLoadPRE(LI, ValuesPerBlock, UnavailableBlocks);
 }
 
+bool GVN::processAssumeIntrinsic(IntrinsicInst *IntrinsicI) {
+  assert(IntrinsicI->getIntrinsicID() == Intrinsic::assume &&
+         "This function can only be called with llvm.assume intrinsic");
+  Value *V = IntrinsicI->getArgOperand(0);
+  Constant *True = ConstantInt::getTrue(V->getContext());
+  bool Changed = false;
+  for (BasicBlock *Successor : successors(IntrinsicI->getParent())) {
+    BasicBlockEdge Edge(IntrinsicI->getParent(), Successor);
+
+    // This property is only true in dominated successors, propagateEquality
+    // will check dominance for us.
+    Changed |= propagateEquality(V, True, Edge);
+  }
+
+  if (auto *CmpI = dyn_cast<CmpInst>(V)) {
+    if (CmpI->getPredicate() == CmpInst::Predicate::ICMP_EQ ||
+        CmpI->getPredicate() == CmpInst::Predicate::FCMP_OEQ ||
+        (CmpI->getPredicate() == CmpInst::Predicate::FCMP_UEQ &&
+         CmpI->getFastMathFlags().noNaNs())) {
+      Value *CmpLHS = CmpI->getOperand(0);
+      Value *CmpRHS = CmpI->getOperand(1);
+      if (isa<Constant>(CmpLHS))
+        std::swap(CmpLHS, CmpRHS);
+      auto *RHSConst = dyn_cast<Constant>(CmpRHS);
+
+      // If only one operand is constant.
+      if (RHSConst != nullptr && !isa<Constant>(CmpLHS))
+        ReplaceWithConstMap[CmpLHS] = RHSConst;
+    }
+  }
+  return Changed;
+}
 
 static void patchReplacementInstruction(Instruction *I, Value *Repl) {
   // Patch the replacement so that it is not more restrictive than the value
@@ -2032,6 +2070,21 @@ static bool isOnlyReachableViaThisEdge(const BasicBlockEdge &E,
   return Pred != nullptr;
 }
 
+// Tries to replace instruction with const, using information from
+// ReplaceWithConstMap.
+bool GVN::replaceOperandsWithConsts(Instruction *Instr) const {
+  bool Changed = false;
+  for (unsigned OpNum = 0; OpNum < Instr->getNumOperands(); ++OpNum) {
+    Value *Operand = Instr->getOperand(OpNum);
+    auto it = ReplaceWithConstMap.find(Operand);
+    if (it != ReplaceWithConstMap.end()) {
+      Instr->setOperand(OpNum, it->second);
+      Changed = true;
+    }
+  }
+  return Changed;
+}
+
 /// The given values are known to be equal in every block
 /// dominated by 'Root'.  Exploit this, for example by replacing 'LHS' with
 /// 'RHS' everywhere in the scope.  Returns whether a change was made.
@@ -2048,11 +2101,13 @@ bool GVN::propagateEquality(Value *LHS, Value *RHS,
     std::pair<Value*, Value*> Item = Worklist.pop_back_val();
     LHS = Item.first; RHS = Item.second;
 
-    if (LHS == RHS) continue;
+    if (LHS == RHS)
+      continue;
     assert(LHS->getType() == RHS->getType() && "Equality but unequal types!");
 
     // Don't try to propagate equalities between constants.
-    if (isa<Constant>(LHS) && isa<Constant>(RHS)) continue;
+    if (isa<Constant>(LHS) && isa<Constant>(RHS))
+      continue;
 
     // Prefer a constant on the right-hand side, or an Argument if no constants.
     if (isa<Constant>(LHS) || (isa<Argument>(LHS) && !isa<Constant>(RHS)))
@@ -2203,6 +2258,10 @@ bool GVN::processInstruction(Instruction *I) {
     return true;
   }
 
+  if (IntrinsicInst *IntrinsicI = dyn_cast<IntrinsicInst>(I))
+    if (IntrinsicI->getIntrinsicID() == Intrinsic::assume)
+      return processAssumeIntrinsic(IntrinsicI);
+
   if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
     if (processLoad(LI))
       return true;
@@ -2267,7 +2326,8 @@ bool GVN::processInstruction(Instruction *I) {
 
   // Instructions with void type don't return a value, so there's
   // no point in trying to find redundancies in them.
-  if (I->getType()->isVoidTy()) return false;
+  if (I->getType()->isVoidTy())
+    return false;
 
   uint32_t NextNum = VN.getNextUnusedValueNumber();
   unsigned Num = VN.lookup_or_add(I);
@@ -2374,10 +2434,15 @@ bool GVN::processBlock(BasicBlock *BB) {
   if (DeadBlocks.count(BB))
     return false;
 
+  // Clearing map before every BB because it can be used only for single BB.
+  ReplaceWithConstMap.clear();
   bool ChangedFunction = false;
 
   for (BasicBlock::iterator BI = BB->begin(), BE = BB->end();
        BI != BE;) {
+    if (!ReplaceWithConstMap.empty())
+      ChangedFunction |= replaceOperandsWithConsts(BI);
+
     ChangedFunction |= processInstruction(BI);
     if (InstrsToErase.empty()) {
       ++BI;