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Matt Arsenault
94bbcd967d
DAG: Stop trying to fold FP -(x-y) -> y-x in getNode with nsz
This was increasing the number of instructions when fsub was legalized on AMDGPU with no signed zeros enabled. This fold should be guarded by hasOneUse, and I don't think getNode should be doing that. The same fold is already done as a regular combine through isNegatibleForFree. This does require duplicating, even though isNegatibleForFree does this combine already (and properly checks hasOneUse) to avoid one PPC regression. In the regression, the outer fneg has nsz but the fsub operand does not. isNegatibleForFree only sees the operand, and doesn't see it's used from a nsz context. A nsz parameter needs to be added and threaded through isNegatibleForFree to avoid this.
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