On Mon, Feb 4, 2019 at 12:08 PM Jakub Jelinek <ja...@redhat.com> wrote: > > On Mon, Feb 04, 2019 at 12:04:04PM +0100, Richard Biener wrote: > > On Mon, Feb 4, 2019 at 10:10 AM Uros Bizjak <ubiz...@gmail.com> wrote: > > > > > > On Fri, Feb 1, 2019 at 10:18 PM H.J. Lu <hjl.to...@gmail.com> wrote: > > > > > > > > On x86-64, since __m64 is returned and passed in XMM registers, we can > > > > implement MMX intrinsics with SSE instructions. To support it, we > > > > disable > > > > MMX by default in 64-bit mode so that MMX registers won't be available > > > > with x86-64. Most of MMX instructions have equivalent SSE versions and > > > > results of some SSE versions need to be reshuffled to the right order > > > > for MMX. Thee are couple tricky cases: > > > > > > I don't think we have to disable MMX registers, but we have to tune > > > register allocation preferences to not allocate MMX register unless > > > really necessary. In practice, this means to change y constraints to > > > *y when TARGET_MMX_WITH_SSE is active (probably using enable > > > attribute). This would solve problem with assembler clobbers that Andi > > > exposed. > > > > But is "unless really necessary" good enough to not have it wrongly > > under any circumstance? I actually like HJs patch (not looked at the > > Or we could disable MMX registers unless they are referenced in inline asm > (clobbers or constraints). > > Anyway, is the patch set meant for GCC9 or GCC10? I'd say it would be quite > dangerous to change this in GCC9.
No, this relatively invasive patchset is definitely meant for GCC10. Uros.
