[llvm-dev] Why does FPBinOp(X, undef) -> NaN?
Cameron McInally via llvm-dev
llvm-dev at lists.llvm.org
Fri Feb 7 09:20:51 PST 2020
I came across this comment in SelectionDAG.cpp:
// If both operands are undef, the result is undef. If 1 operand is undef,
// the result is NaN. This should match the behavior of the IR optimizer.
That isn't intuitive to me. I would have expected a binary FP
operation with one undef operand to fold to undef. Does anyone know
the reasoning behind that decision? I don't see the value added in
returning a NaN here.
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