[InstCombine] simplify fneg+fadd folds; NFC

Two cleanups:
1. As noted in D45453, we had tests that don't need FMF that were misplaced in the 'fast-math.ll' test file.
2. This removes the final uses of dyn_castFNegVal, so that can be deleted. We use 'match' now.

llvm-svn: 330126

llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp

@@ -1308,14 +1308,13 @@ Instruction *InstCombiner::visitFAdd(BinaryOperator &I) {
   if (Instruction *FoldedFAdd = foldBinOpIntoSelectOrPhi(I))
     return FoldedFAdd;
 
-  // -A + B  -->  B - A
-  if (Value *LHSV = dyn_castFNegVal(LHS))
-    return BinaryOperator::CreateFSubFMF(RHS, LHSV, &I);
-
-  // A + -B  -->  A - B
-  if (!isa<Constant>(RHS))
-    if (Value *V = dyn_castFNegVal(RHS))
-      return BinaryOperator::CreateFSubFMF(LHS, V, &I);
+  Value *X;
+  // (-X) + Y --> Y - X
+  if (match(LHS, m_FNeg(m_Value(X))))
+    return BinaryOperator::CreateFSubFMF(RHS, X, &I);
+  // Y + (-X) --> Y - X
+  if (match(RHS, m_FNeg(m_Value(X))))
+    return BinaryOperator::CreateFSubFMF(LHS, X, &I);
 
   // Check for (fadd double (sitofp x), y), see if we can merge this into an
   // integer add followed by a promotion.

llvm/lib/Transforms/InstCombine/InstCombineInternal.h

@@ -376,7 +376,6 @@ private:
   bool shouldChangeType(unsigned FromBitWidth, unsigned ToBitWidth) const;
   bool shouldChangeType(Type *From, Type *To) const;
   Value *dyn_castNegVal(Value *V) const;
-  Value *dyn_castFNegVal(Value *V, bool NoSignedZero = false) const;
   Type *FindElementAtOffset(PointerType *PtrTy, int64_t Offset,
                             SmallVectorImpl<Value *> &NewIndices);
 

llvm/lib/Transforms/InstCombine/InstructionCombining.cpp

@@ -790,23 +790,6 @@ Value *InstCombiner::dyn_castNegVal(Value *V) const {
   return nullptr;
 }
 
-/// Given a 'fsub' instruction, return the RHS of the instruction if the LHS is
-/// a constant negative zero (which is the 'negate' form).
-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.
-  if (ConstantFP *C = dyn_cast<ConstantFP>(V))
-    return ConstantExpr::getFNeg(C);
-
-  if (ConstantDataVector *C = dyn_cast<ConstantDataVector>(V))
-    if (C->getType()->getElementType()->isFloatingPointTy())
-      return ConstantExpr::getFNeg(C);
-
-  return nullptr;
-}
-
 static Value *foldOperationIntoSelectOperand(Instruction &I, Value *SO,
                                              InstCombiner::BuilderTy &Builder) {
   if (auto *Cast = dyn_cast<CastInst>(&I))

llvm/test/Transforms/InstCombine/fadd.ll

@@ -0,0 +1,27 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt < %s -instcombine -S | FileCheck %s
+
+; -x + y => y - x
+
+define float @fneg_op0(float %x, float %y) {
+; CHECK-LABEL: @fneg_op0(
+; CHECK-NEXT:    [[ADD:%.*]] = fsub float [[Y:%.*]], [[X:%.*]]
+; CHECK-NEXT:    ret float [[ADD]]
+;
+  %neg = fsub float -0.0, %x
+  %add = fadd float %neg, %y
+  ret float %add
+}
+
+; x + -y => x - y
+
+define float @fneg_op1(float %x, float %y) {
+; CHECK-LABEL: @fneg_op1(
+; CHECK-NEXT:    [[ADD:%.*]] = fsub float [[X:%.*]], [[Y:%.*]]
+; CHECK-NEXT:    ret float [[ADD]]
+;
+  %neg = fsub float -0.0, %y
+  %add = fadd float %x, %neg
+  ret float %add
+}
+

llvm/test/Transforms/InstCombine/fast-math.ll

@@ -406,30 +406,6 @@ define float @fold13_reassoc(float %x) {
   ret float %sub
 }
 
-; -x + y => y - x
-; This is always safe.  No FMF required.
-define float @fold14(float %x, float %y) {
-; CHECK-LABEL: @fold14(
-; CHECK-NEXT:    [[ADD:%.*]] = fsub float [[Y:%.*]], [[X:%.*]]
-; CHECK-NEXT:    ret float [[ADD]]
-;
-  %neg = fsub float -0.0, %x
-  %add = fadd float %neg, %y
-  ret float %add
-}
-
-; x + -y => x - y
-; This is always safe.  No FMF required.
-define float @fold15(float %x, float %y) {
-; CHECK-LABEL: @fold15(
-; CHECK-NEXT:    [[ADD:%.*]] = fsub float [[X:%.*]], [[Y:%.*]]
-; CHECK-NEXT:    ret float [[ADD]]
-;
-  %neg = fsub float -0.0, %y
-  %add = fadd float %x, %neg
-  ret float %add
-}
-
 ; (select X+Y, X-Y) => X + (select Y, -Y)
 ; This is always safe.  No FMF required.
 define float @fold16(float %x, float %y) {