RE: [Caml-list] Closing the performance gap to C

["Soegtrop, Michael" <michael.soegtrop@intel.com>]

Dear Gerd,

> When you call a C function like cos it is likely that this
> happens because the C calling conventions do not preserve the FP registers
> (xmm*). This could be improved if the OCaml compiler tried alternate places for
> temporarily storing FP values:

For Windows this doesn't seem to be true. See e.g.:

https://msdn.microsoft.com/en-us/library/ms235286.aspx

which states that XMM0..XMM5 are volatile, while XMM6..XMM15 must be preserved.

I think for Linix you are right. I couldn't find a better reference than Wikipedia:

https://en.wikipedia.org/wiki/X86_calling_conventions

see "System V AMD64 ABI" there.
 
This reference contains a good overview, which matches the above data in table 4:

http://www.agner.org/optimize/calling_conventions.pdf

So on Windows, there is for sure no need to save XMM6..XMM15, while on Linux this seems to be an issue.

Best regards,

Michael
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