[llvm-dev] RFC: Consider changing the semantics of 'fast' flag implying all fast-math-flags

[Nicolai Hähnle via llvm-dev]

On 17.11.2016 22:09, Hal Finkel wrote:
> Yes and no. For one thing, *all* FP contraction modes (i.e. FMA formation), including the one standardized by C, can change results doing to different intermediate rounding properties. What makes it different from other "fast math" settings is that:
>
>  1. The result from individual contracted operations is always more accurate than the original operations, not less.
>  2. The FMA operation, which is the only combination that FP contraction enables, is a specific combination that is defined by the IEEE standard.
>
> For these reasons, we differentiate it from the others, and users also consider it qualitatively different from other FP optimization flags.

That makes sense, thank you for the clarification!

Nicolai