[InstCombine] FP: Z - (X - Y) --> Z + (Y - X)
This restores what was lost with rL73243 but without
re-introducing the bug that was present in the old code.
Note that we already have these transforms if the ops are
marked 'fast' (and I assume that's happening somewhere in
the code added with rL170471), but we clearly don't need
all of 'fast' for these transforms.
llvm-svn: 329362
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
index 0541eb7..fac3ea8 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
@@ -1698,6 +1698,7 @@
SQ.getWithInstruction(&I)))
return replaceInstUsesWith(I, V);
+ Value *X, *Y;
if (I.hasNoSignedZeros()) {
// Subtraction from -0.0 is the canonical form of fneg.
// fsub nsz 0, X ==> fsub nsz -0.0, X
@@ -1705,11 +1706,20 @@
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);
}
+ // More generally than above, if Op0 is not -0.0: Z - (X - Y) --> Z + (Y - X)
+ // Canonicalize to fadd to make analysis easier.
+ // This can also help codegen because fadd is commutative.
+ if (I.hasNoSignedZeros() || CannotBeNegativeZero(Op0, SQ.TLI)) {
+ if (match(Op1, m_OneUse(m_FSub(m_Value(X), m_Value(Y))))) {
+ Value *NewSub = Builder.CreateFSubFMF(Y, X, &I);
+ return BinaryOperator::CreateFAddFMF(Op0, NewSub, &I);
+ }
+ }
+
if (isa<Constant>(Op0))
if (SelectInst *SI = dyn_cast<SelectInst>(Op1))
if (Instruction *NV = FoldOpIntoSelect(I, SI))
@@ -1721,7 +1731,6 @@
return BinaryOperator::CreateFAddFMF(Op0, ConstantExpr::getFNeg(C), &I);
// X - (-Y) --> X + Y
- Value *Y;
if (match(Op1, m_FNeg(m_Value(Y))))
return BinaryOperator::CreateFAddFMF(Op0, Y, &I);