[llvm-dev] how to simplify FP ops with an undef operand?

[Matt Arsenault via llvm-dev]

> On Mar 2, 2018, at 14:45, Kaylor, Andrew <andrew.kaylor at intel.com> wrote:
> 
> Well, using ConstantFP to represent NaNs is at least unclear enough that someone claimed that there is no NaN constant in LLVM IR. :-)
> 
> But your point is well made. I guess what I was really asking for is a 'NaN' token in the asm writer/parser. This is obviously a much less important issue, but I can't say that I would look at 0x7f800000 in an ll file and immediately think, "Oh, that's a NaN." I'm not a fan of hexadecimal representation of floating point numbers in general, but I guess it's a necessary evil for exact conversion back to bitcode. The 'NaN' I'm asking for, of course, has something like 4 million possible representations, but I think they are all equivalent.
> 
> In short, never mind.

One issue I’ve always had is the nonsensical use of double FP constants even for float values. I can recognize the special FP values if they appear in their natural 4-byte format, but when awkwardly converted to double it’s more difficult, especially when I’ve written tests checking for the correct handling of payload bits.

-Matt
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