[PATCH] D25297: [DAG] use SDNode flags 'nsz' to enable fadd/fsub with zero folds

[Sanjay Patel via llvm-commits]

spatel created this revision.
spatel added reviewers: mehdi_amini, echristo, hfinkel.
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As discussed in https://reviews.llvm.org/D24815, let's start the process of killing off the broken fast-math global state housed in TargetOptions and eliminate the need for function-level fast-math attributes.

Looks like I started this mission in https://reviews.llvm.org/D9708...and promptly got distracted for almost a year. :)

Here we enable two similar folds that are possible when we don't care about signed-zero:
fadd nsz x, 0 --> x
fsub nsz 0, x --> -x

Note that although the test cases include a 'sin' function call, I'm side-stepping the FMF-on-calls question (and lack of support in the DAG) for now. It's not needed for these tests - isNegatibleForFree/GetNegatedExpression just look through a ISD::FSIN node.


https://reviews.llvm.org/D25297

Files:
  lib/CodeGen/SelectionDAG/DAGCombiner.cpp
  test/CodeGen/X86/negative-sin.ll

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