[LLVMdev] Pure external functions

[Lennart Augustsson]

You need to set the readnone attribute.  I set it on the call instruction.

  -- Lennart

On Tue, Feb 17, 2009 at 10:37 AM, Jon Harrop <jon at ffconsultancy.com> wrote:
> On Tuesday 17 February 2009 09:46:07 Duncan Sands wrote:
>> Hi,
>>
>> > Lennart Augustsson mentioned on his blog that he got substantial
>> > performance improvements by conveying to LLVM when external functions
>> > (e.g. tanh) were pure.
>>
>> first note that tanh is not pure, because the result depends on the current
>> floating point rounding mode.
>
> Ugh.
>
>> However, if you are willing to sacrifice
>> complete numerical correctness, you can give llvm-gcc the -ffast-math flag
>> and, voila!, tanh becomes pure.
>
> How do you do the equivalent from the JIT?
>
> --
> Dr Jon Harrop, Flying Frog Consultancy Ltd.
> http://www.ffconsultancy.com/?e
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