[llvm-dev] [FPEnv] Do we need constrained/strict versions of these intrinsics?

Connor Abbott via llvm-dev llvm-dev at lists.llvm.org
Wed Dec 11 06:07:54 PST 2019

On Wed, Dec 11, 2019 at 2:51 PM Ulrich Weigand via llvm-dev
<llvm-dev at lists.llvm.org> wrote:
> Following up on myself after some further investigation:
> >Craig Topper wrote:
> >
> >>I was thinking about a few less common floating point things and wondered
> >>if we need constrained/strict versions of them.
> >>
> >>-int_fmuladd - which is used by clang to support fp-contract=on where only
> >>operations within a statement sare allowed to be concentrated.
> >
> >Probably yes.
> OTOH this is also solely an optimization, so for now we could
> simply have clang not generate those when in strict mode.
> >I'm also seeing the following additional intrinsics:
> >
> >- int_canonicalize
> >I believe we need a strict version of this as well.
> It seems like this is currently only supported on AMDGPU
> and will simply trigger an internal error everywhere else.
> (I thought there was a default expansion to a multiply
> with 1.0 or something, but apparently not ...)
> Given that, I don't think we need a strict version
> either (at least not straight away).

We'll definitely want a strict version of this on AMDGPU, because
Vulkan now allows you to set different denorm-flushing modes, and to
implement it we'll sometimes need to change the setting in the middle
of a function.

> >- int_maximum/int_minimum
> >This is currently only generated by clang to implement some WebAssembly
> >builtins, but adding strict support to parallel maxnum/minnum should
> >be straightforward.
> I have a patch for those, which I'll post after D71218 is in.
> Bye,
> Ulrich
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