[clang] [clang] Set correct FPOptions if attribute 'optnone' presents (PR #85605)

[John McCall via cfe-commits]

rjmccall wrote:

Hmm.  Is there some sort of optimization in IRGen that we need to suppress here, or is it something in LLVM code gen?  Presumably normal LLVM optimization passes all just skip `optnone` functions.

Mostly I'm wondering how far we're expected to go with `optnone`.

https://github.com/llvm/llvm-project/pull/85605