[PATCH] D157388: [AMDGPU] Support FMin/FMax in AMDGPUAtomicOptimizer.

[Matt Arsenault via Phabricator via llvm-commits]

arsenm added inline comments.


================
Comment at: llvm/lib/Target/AMDGPU/AMDGPUAtomicOptimizer.cpp:405
+  case AtomicRMWInst::FMax:
+    return B.CreateSelect(B.CreateFCmp(FCmpInst::FCMP_UGT, LHS, RHS), LHS, RHS);
+  case AtomicRMWInst::FMin:
----------------
arsenm wrote:
> pravinjagtap wrote:
> > @arsenm you earlier suggested to use minnum/maxnum intrinsics for this. This also seems to give correct behavior. I am not sure what I am missing here 
> This is incorrect, you should create minnum/maxnum
Yes, it is wrong to use fcmp and select here. For example for fmax what you have returns the wrong result if LHS is a nan.

 select (ugt nan, rhs), nan, rhs -> nan
 maxnum(nan, rhs) -> rhs


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  https://reviews.llvm.org/D157388/new/

https://reviews.llvm.org/D157388