[LLVMdev] Best way for JIT to query whether llvm.fma.* is fast?

[Lang Hames]

Hi Arch,

Also, consider just emitting the llvm.fmuladd intrinsic instead of
llvm.fma. fmuladd is lowered to llvm.fma in codegen if the optimizer
determines that it's beneficial, otherwise it is expanded to a mul and an
add.

At the moment I think SelectionDAG is just checking isFMAFasterThanFMulAndFAdd
anyway, but that condition could be refined in the future.

Cheers,
Lang.


On Wed, Dec 10, 2014 at 1:17 PM, Robison, Arch <arch.robison at intel.com>
wrote:

>  Thanks!  That’s probably close enough for practical purposes.  I looked
> at the overrides on various targets, and they all return true if the FMA
> hardware exists.
>
>
>
> - Arch
>
>
>
> *From:* Jingyue Wu [mailto:jingyue at google.com]
> *Sent:* Wednesday, December 10, 2014 2:56 PM
> *To:* Robison, Arch
> *Cc:* llvmdev at cs.uiuc.edu
> *Subject:* Re: [LLVMdev] Best way for JIT to query whether llvm.fma.* is
> fast?
>
>
>
> Does TargetLowering::isFMAFasterThanFMulAndFAdd (
> http://llvm.org/docs/doxygen/html/TargetLowering_8h_source.html#l01499)
> help?
>
>
>
> Jingyue
>
>
>
> On Wed, Dec 10, 2014 at 12:48 PM, Robison, Arch <arch.robison at intel.com>
> wrote:
>
>  For the Julia language JIT, we’d like be able to tell whether the
> llvm.fma.* intrinsic has hardware support.  What’s the best way to  query
> LLVM (JIT) for this information?
>
>
>
> The information would be used in situations where the user wants to use
> different algorithms depending on whether FMA hardware is present or not.
>
>
>
> - Arch D. Robison
>
>
>
>
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