[PATCH] D143074: [LangRef] improve documentation of SNaN in the default FP environment

[Ralf via Phabricator via llvm-commits]

RalfJung added a comment.

> because, from what I understand, before IEEE 754 specified how to encode quietness for NaNs, MIPS (and PA-RISC) arbitrarily chose the opposite encoding to what IEEE 754-2008 specifies, so LLVM generating quiet NaNs following IEEE 754-2008 produces NaNs that are actually signalling NaNs for old MIPS. MIPS later added a mode bit allowing swapping its interpretation of signalling/quiet NaNs to fall in line with the IEEE 754-2008 spec -- new MIPS has that set to IEEE 754-2008 mode.

Sorry, I should have clarified, I was asking specifically about this part:
"There's just no way it's okay to spuriously introduce sNaNs when the original program didn't contain sNaNs in the first place."


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https://reviews.llvm.org/D143074