[PATCH] D62731: [RFC] Add support for options -fp-model= and -fp-speculation= : specify floating point behavior

Wed Aug 7 14:39:50 PDT 2019

mibintc added a comment.

In D62731#1603030 <https://reviews.llvm.org/D62731#1603030>, @kpn wrote:

> I actually don't have much of an opinion on what the command line argument form should be. It may be helpful for it to be the same as one of the commonly deployed compilers. The worst I think would be pretty close but with subtle differences. So if it can be made to work like Intel's compiler I'm fine with that. But I'm hoping that more people in the community chime in since having a consensus would be best. Personally, I'm not yet giving any final sign-offs to tickets since I don't think I've been here long enough.
>
> As far as the rounding metadata argument, the language reference says this:
>
> > For values other than “round.dynamic” optimization passes may assume that the actual runtime rounding mode (as defined in a target-specific manner) matches the specified rounding mode, but this is not guaranteed. Using a specific non-dynamic rounding mode which does not match the actual rounding mode at runtime results in undefined behavior.
>
> Be aware that currently neither of the metadata arguments does anything. They get dropped when llvm reaches the SelectionDAG. And none of the optimization passes that run before that know anything about constrained intrinsics at all. This means they treat code that has them conservatively. Preserving and using that metadata in the optimization passes and getting it down and used by the MI layer is planned but hasn't happened yet. So the full set of arguments may not make sense yet, but an on/off switch for strict mode hopefully does.

@andrew.w.kaylor Can you please check over Kevin's comments about metadata?

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https://reviews.llvm.org/D62731