Re: [PATCH v4] x86-64: Use R11 for DRAP register in preserve_none functions

[Uros Bizjak]

On Wed, May 13, 2026 at 9:29 AM H.J. Lu <hjl.to...@gmail.com> wrote:
>
> On Wed, May 13, 2026 at 1:50 PM Uros Bizjak <ubiz...@gmail.com> wrote:
> >
> > On Wed, May 13, 2026 at 12:00 AM H.J. Lu <hjl.to...@gmail.com> wrote:
> > >
> > > In 64-bit mode, for preserve_none functions, DRAP may use any register
> > > except AX, R12–R15, DI, SI (argument registers), SP, and BP. Use R11.
> > > In non-callee-saved functions, R10 and R13 are also available since they
> > > are not used for parameter passing.  In 32-bit mode, preserve_none does
> > > not affect parameter passing, so the current approach remains valid.
> > >
> > > DRAP register is used to restore stack pointer in epilogue for stack
> > > realignment.  Always save and restore DRAP register between prologue
> > > and epilogue so that stack pointer can be restored.
> > >
> > > Tested on Linux/x86-64 and with CPython 3.14.4.
> > >
> > > gcc/
> > >
> > > PR target/120870
> > > * config/i386/i386.cc (ix86_save_reg): Return true for DRAP
> > > register early at entry.
> > > (find_drap_reg): Use R11_REG in preserve_none functions in
> > > 64-bit mode.
> > >
> > > gcc/testsuite/
> > >
> > > PR target/120870
> > > * gcc.target/i386/pr120870-1.c: New test.
> > > * gcc.target/i386/pr120870-2.c: Likewise.
> >
> > +
> > +__attribute__ ((preserve_none)) void
> > +tail (long a, long b)
> > +{
> > +}
> >
> > This function doesn't need to be preserve_none, and the test will
> > still fail with the unpatched compiler.
> >
> > OK with the above adjustion.
>
> Fixed.
>
> > Thanks,
> > Uros.
>
> This is what I am checking in.  OK to backport to GCC 16 branch
> after a few days?

OK.

Thanks,
Uros.