[llvm] [DAG] SelectionDAG::canCreateUndefOrPoison - add ISD::FMA/FMAD + tests (PR #152187)

[via llvm-commits]

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@@ -5622,6 +5622,8 @@ bool SelectionDAG::canCreateUndefOrPoison(SDValue Op, const APInt &DemandedElts,
   case ISD::FDIV:
   case ISD::FREM:
   case ISD::FCOPYSIGN:
+  case ISD::FMA:
+  case ISD::FMAD:   
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Seraphimt wrote:

I rely on words @RKSimon in task: 
> the freeze between the fneg and the fma is preventing the fold into fnmadd from occurring. But if the compiler knows ISD::FMA doesn't create undef/poison itself then its enough to freeze the inputs like in @tgt (as that's the only place that undef/poison can come from) 
https://github.com/llvm/llvm-project/issues/147693#issuecomment-3061036980

So why in poison argument case fma + freeze + fneg turn into fnmadd still? 

https://github.com/llvm/llvm-project/pull/152187