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Re: Add an "early rematerialisation" pass
On Fri, Dec 15, 2017 at 08:14:38PM +0100, Richard Biener wrote:
> On December 15, 2017 8:10:33 PM GMT+01:00, Jeff Law <law@redhat.com> wrote:
> >On 12/14/2017 12:32 PM, Richard Biener wrote:
> >>
> >> On x86_64 all xmm registers are caller saved for example. That means
> >all FP regs and all vectors. (yeah, stupid ABI decision....)
> >But that's precisely what I would expect if one was looking to maintain
> >backwards compatibility within the core runtime libraries.
> >
> >If you make something callee-saved, then you have to have space for it
> >in the setjmp buffer. Expanding that buffer is an ABI change and thus
> >*highly* discouraged.
>
> Yes. But the initial 64bit ABI already had 8 xmm regs. Probably all used for parameter passing as well, but...
>
> For all further extensions I agree.
Another issue is that the ?mm registers keep growing in size, and having
e.g. low 128-bits of the registers call-saved and upper bits call-used is
just weird (I believe that is the MS ABI).
Jakub