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

Melanie Blower via Phabricator via cfe-commits cfe-commits at lists.llvm.org
Wed Aug 7 14:38:27 PDT 2019


mibintc added a comment.

In D62731#1601408 <https://reviews.llvm.org/D62731#1601408>, @kpn wrote:

> In D62731#1601310 <https://reviews.llvm.org/D62731#1601310>, @mibintc wrote:
>
> > I think it would be convenient to have an "unset" setting for the different constrained modes, otherwise you need a boolean that says "no value was provided for this option".  But i'm a frontend person so I may need to have my attitude adjusted.
>
>
> What "different constrained modes"? The IRBuilder is either in constrained mode or it isn't. In constrained mode the exception behavior and rounding mode both have defaults, and those defaults can be changed individually without affecting the other setting. The current defaults can also be retrieved if you need something for a function call where you don't want to change it but need an argument anyway. When do you need this "no value provided" setting?
>
> Oh, I'd check the tools/clang/CODE_OWNERS.txt file and add additional appropriate reviewers. Perhaps John McCall and Richard Smith? I don't know who has opinions on how command line options should be handled.
>
> Do we want the Unix driver to be compatible with gcc? Maybe, maybe not. Opinions, anyone?


Yes we need opinions on this.

> The documentation request from lebedev.ri isn't in this ticket yet.

I'm not yet sure what I need for this, the requested documentation is still missing.

> Also, for future historical research purposes I'd cut and paste the relevant portions of outside web pages (like intel.com's) and post them somewhere llvm-ish where they are findable. This ticket, for example, is a good place. Web sites gets reorganized or vanish in full or in part. It's helpful to have some insulation from that over time. I've had to fix compiler bugs that actually were 25 years old before. Yes, 25 years old. Being able to do the research is very helpful.
> 
> Oh, it may be useful to know that constrained floating point and the FastMathFlags are not mutually exclusive. I don't know if that matters here or not, but you did mention FastMathFlags.

Yes they aren't mutually exclusive.  One of the fp-model options implies enabling fast math.


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