Re: [PATCH v3] x86: Disable SSE on unwind-c.c and unwind-dw2.c

[Jakub Jelinek <jakub@redhat.com>]

On Tue, Mar 08, 2022 at 12:15:15PM +0100, Jakub Jelinek via Gcc-patches wrote:
> > --- gcc/config/i386/i386.h.jj	2022-02-25 12:06:45.535493490 +0100
> > +++ gcc/config/i386/i386.h	2022-03-08 11:20:43.207043370 +0100
> > @@ -2848,6 +2848,10 @@ extern enum attr_cpu ix86_schedule;
> >  #define NUM_X86_64_MS_CLOBBERED_REGS 12
> >  #endif
> >  
> > +/* __builtin_eh_return can't handle stack realignment, so disable SSE in
> > +   libgcc functions that call it.  */
> > +#define LIBGCC2_UNWIND_ATTRIBUTE __attribute__((target ("no-sse")))
> > +
> >  /*
> >  Local variables:
> >  version-control: t
> > 
> > 
> > As mentioned in PR104838, this likely isn't specific to just Solaris and
> > cygwin/mingw.  Fedora uses -msse2 -mfpmath=sse -mstackrealign in its C{,XX}FLAGS
> > among other things for i686.
> 
> Now verified that with your full patch applied gcc on Fedora/i686 doesn't
> build (gets those sorry messages when compiling unwind-dw2), while if I
> replace those 2 libgcc hunks from your patch with the above one it seems to
> get past the previous hanging point of gnat1 processes.

Though, perhaps it should be
#ifndef __x86_64__
#define LIBGCC2_UNWIND_ATTRIBUTE __attribute__((target ("no-sse")))
#endif
or something similar, on x86-64 one at least normally doesn't use lower
stack realignment unless avx or later.  Maybe we want to use
no-avx for the x86-64 case though.
Disabling sse/sse2 might be a problem especially on mingw where we need to
restore SSE registers in the EH return, no?

Even better would be to make __builtin_eh_return work even with DRAP,
but I admit I haven't understood what exactly is the problem that prevents
it from working.

	Jakub