[InstCombine] nsz: -(X - Y) --> Y - X
This restores part of the fold that was removed with rL73243 (PR4374).
llvm-svn: 329350
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
index 578ba23..0541eb7 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
@@ -1698,10 +1698,17 @@
SQ.getWithInstruction(&I)))
return replaceInstUsesWith(I, V);
- // Subtraction from -0.0 is the canonical form of fneg.
- // fsub nsz 0, X ==> fsub nsz -0.0, X
- if (I.getFastMathFlags().noSignedZeros() && match(Op0, m_PosZeroFP()))
- return BinaryOperator::CreateFNegFMF(Op1, &I);
+ if (I.hasNoSignedZeros()) {
+ // Subtraction from -0.0 is the canonical form of fneg.
+ // fsub nsz 0, X ==> fsub nsz -0.0, X
+ if (match(Op0, m_PosZeroFP()))
+ return BinaryOperator::CreateFNegFMF(Op1, &I);
+
+ // With no-signed-zeros: -(X - Y) --> Y - X
+ Value *X, *Y;
+ if (match(Op0, m_NegZeroFP()) && match(Op1, m_FSub(m_Value(X), m_Value(Y))))
+ return BinaryOperator::CreateFSubFMF(Y, X, &I);
+ }
if (isa<Constant>(Op0))
if (SelectInst *SI = dyn_cast<SelectInst>(Op1))