Consider expression "0.0 - X" as the negation of X if

  - this expression is explicitly marked no-signed-zero, or
  - no-signed-zero of this expression can be derived from some context.

llvm-svn: 171922

4 files changed, 18 insertions, 6 deletions

diff --git a/llvm/lib/IR/Constants.cpp b/llvm/lib/IR/Constants.cpp
index 4b585999554..812692f3fae 100644
--- a/llvm/lib/IR/Constants.cpp
+++ b/llvm/lib/IR/Constants.cpp
@@ -51,6 +51,15 @@ bool Constant::isNegativeZeroValue() const {
   return isNullValue();
 }
 
+bool Constant::isZeroValue() const {
+  // Floating point values have an explicit -0.0 value.
+  if (const ConstantFP *CFP = dyn_cast<ConstantFP>(this))
+    return CFP->isZero();
+
+  // Otherwise, just use +0.0.
+  return isNullValue();
+}
+
 bool Constant::isNullValue() const {
   // 0 is null.
   if (const ConstantInt *CI = dyn_cast<ConstantInt>(this))
diff --git a/llvm/lib/IR/Instructions.cpp b/llvm/lib/IR/Instructions.cpp
index 1b5d004978c..f2e9813bc63 100644
--- a/llvm/lib/IR/Instructions.cpp
+++ b/llvm/lib/IR/Instructions.cpp
@@ -1926,11 +1926,14 @@ bool BinaryOperator::isNeg(const Value *V) {
   return false;
 }
 
-bool BinaryOperator::isFNeg(const Value *V) {
+bool BinaryOperator::isFNeg(const Value *V, bool IgnoreZeroSign) {
   if (const BinaryOperator *Bop = dyn_cast<BinaryOperator>(V))
     if (Bop->getOpcode() == Instruction::FSub)
-      if (Constant* C = dyn_cast<Constant>(Bop->getOperand(0)))
-        return C->isNegativeZeroValue();
+      if (Constant* C = dyn_cast<Constant>(Bop->getOperand(0))) {
+        if (!IgnoreZeroSign)
+          IgnoreZeroSign = cast<Instruction>(V)->hasNoSignedZeros();
+        return !IgnoreZeroSign ? C->isNegativeZeroValue() : C->isZeroValue();
+      }
   return false;
 }
 
diff --git a/llvm/lib/Transforms/InstCombine/InstCombine.h b/llvm/lib/Transforms/InstCombine/InstCombine.h
index 959daa258d8..a36b1e6b9e5 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombine.h
+++ b/llvm/lib/Transforms/InstCombine/InstCombine.h
@@ -211,7 +211,7 @@ public:
 private:
   bool ShouldChangeType(Type *From, Type *To) const;
   Value *dyn_castNegVal(Value *V) const;
-  Value *dyn_castFNegVal(Value *V) const;
+  Value *dyn_castFNegVal(Value *V, bool NoSignedZero=false) const;
   Type *FindElementAtOffset(Type *Ty, int64_t Offset, 
                                   SmallVectorImpl<Value*> &NewIndices);
   Instruction *FoldOpIntoSelect(Instruction &Op, SelectInst *SI);
diff --git a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
index 6f24cdd738c..dc7fe5cf6b5 100644
--- a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -516,8 +516,8 @@ Value *InstCombiner::dyn_castNegVal(Value *V) const {
 // instruction if the LHS is a constant negative zero (which is the 'negate'
 // form).
 //
-Value *InstCombiner::dyn_castFNegVal(Value *V) const {
-  if (BinaryOperator::isFNeg(V))
+Value *InstCombiner::dyn_castFNegVal(Value *V, bool IgnoreZeroSign) const {
+  if (BinaryOperator::isFNeg(V, IgnoreZeroSign))
     return BinaryOperator::getFNegArgument(V);
 
   // Constants can be considered to be negated values if they can be folded.