Re: [PATCH] x86: Use BX_REG for DRAP register in preserve_none function

[Uros Bizjak]

On Tue, May 12, 2026 at 8:23 AM H.J. Lu <hjl.to...@gmail.com> wrote:
>
> On Tue, May 12, 2026 at 2:13 PM Uros Bizjak <ubiz...@gmail.com> wrote:
> >
> > On Tue, May 12, 2026 at 2:42 AM H.J. Lu <hjl.to...@gmail.com> wrote:
> > >
> > > DRAP register is used to restore stack pointer in epilogue for stack
> > > realignment.  In no-callee-saved and preserve_none functions, although
> > > DRAP register isn't preserved, it must be unchanged between prologue
> > > and epilogue so that stack pointer can be restored.  In no-callee-saved
> > > and preserve_none functions, mark BX_REG as fixed and use it for DRAP
> > > register.
> > >
> > > NB: r12-r15 aren't made available as the local general purpose registers
> > > since it causes:
> > >
> > > FAIL: gcc.target/i386/preserve-none-1.c scan-assembler-not movq
> > > FAIL: gcc.target/i386/preserve-none-30a.c check-function-bodies entry
> > > FAIL: gcc.target/i386/preserve-none-30b.c check-function-bodies entry
> > >
> > > which have the same cause as
> > >
> > > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=124798
> > >
> > > gcc/
> > >
> > > PR target/120870
> > > * config/i386/i386.cc (X86_NO_CALLEE_DRAP_REG): New.
> > > (ix86_conditional_register_usage): Mark X86_NO_CALLEE_DRAP_REG
> > > as fixed.
> > > (find_drap_reg): Return X86_PRESERVE_NONE_DRAP_REG for
> > > no-callee-saved and preserve_none functions
> > >
> > > gcc/testsuite/
> > >
> > > PR target/120870
> > > * gcc.target/i386/pr120870-1.c: New test.
> > > * gcc.target/i386/pr120870-2.c: Likewise.
> >
> > +      /* Disabled to avoid
> > +
> > +FAIL: gcc.target/i386/preserve-none-1.c scan-assembler-not movq
> > +FAIL: gcc.target/i386/preserve-none-30a.c check-function-bodies entry
> > +FAIL: gcc.target/i386/preserve-none-30b.c check-function-bodies entry
> > +
> > +         which have the same cause as
> > +
> > +         https://gcc.gnu.org/bugzilla/show_bug.cgi?id=124798
> > +
> > +       */
> > +      if (0 && TARGET_64BIT)
> > +        {
> > +          /* Make R12_REG, R13_REG, R14_REG, R15_REG available as
> > +         the local general purpose registers.  */
> > +          call_used_regs[R12_REG] = 1;
> > +          call_used_regs[R13_REG] = 1;
> > +          call_used_regs[R14_REG] = 1;
> > +          call_used_regs[R15_REG] = 1;
> > +        }
> >
> > Why is this disabled part needed in this particular patch?
> >
>
> I am working on a fix to enable it.  Should I sent a v2 patch
> without it?

Yes, please. Otherwise it is just confusing to mix unrelated issues in
the patch.

Uros.