[PATCH] D158053: [Legalizer] Expand fmaximum and fminimum

[Artem Belevich via Phabricator via llvm-commits]

tra added inline comments.


================
Comment at: llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp:8161
+        *DAG.getContext(), APFloat::getNaN(DAG.EVTToAPFloatSemantics(VT)));
+    MinMax = DAG.getSelect(DL, VT, DAG.getSetCC(DL, CCVT, LHS, RHS, ISD::SETUO),
+                           DAG.getConstantFP(*FPNaN, DL, VT), MinMax);
----------------
qiucf wrote:
> tra wrote:
> > Are we expected to return *a* NaN or the specific NaN value of one of the arguments? 
> > APfloat's implementation returns one of the argument values.
> > X86ISelLowering.cpp does the same.
> > 
> > 
> Does the standard specify if the exact NaN should be returned? Choosing one NaN will produce more complex code. 
I don't have access to the standard text. All I could find online are these notes https://grouper.ieee.org/groups/msc/ANSI_IEEE-Std-754-2019/background/minNum_maxNum_Removal_Demotion_v3.pdf oulining the state of the min/max and the recommeendations for the standard changes. They do seem to care about NaN associativity/commutativity, but I have no idea what exactly ended up specified by the standard.

I assume that the authors of the implementations in APFloat and X86 did implement it according to the standard.

@tlively -- would you happen to know the details?


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https://reviews.llvm.org/D158053