[PATCH] D74436: Change clang option -ffp-model=precise to select ffp-contract=on

[John McCall via Phabricator via cfe-commits]

rjmccall added a comment.

Yeah, I agree with Steve here.  The great virtue of `-ffp-contract=on` over the more aggressive modes is that FMA formation is purely local to a single source expression, which means there's really no obstacle to treating it as implementation-guaranteed semantics.  Such behavior should be done consistently across compiler settings rather than potentially making the numeric result of an expression subject to optimizer settings and choices; the latter is fine for "fast" modes but not really acceptable as the default compiler behavior.  If a backend needs to legalize the intrinsic back to separate multiply + add instructions, that's okay, but it should do so consistently rather than only under a specific optimization level.


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D74436/new/

https://reviews.llvm.org/D74436