https://gcc.gnu.org/bugzilla/show_bug.cgi?id=125266
--- Comment #16 from Richard Sandiford <rsandifo at gcc dot gnu.org> ---
(In reply to H.J. Lu from comment #15)
> (In reply to Richard Sandiford from comment #14)
>
> >
> > I don't know if you've looked at it, but aarch64 already uses function_abi
> > for preserve_none. Like x86, aarch64 allows the target to be changed with
> > function attributes, which has the effect of enabling and disabling
> > registers. But aarch64_conditional_register_usage doesn't depend on cfun at
> > all.
>
> Yes, I did. But I am not sure if it works correctly for all cases. For
>
> extern void ext (long a, long b, long c, long d, long e, long f,
> long g, long *);
>
> extern void tail (long a, long b) __attribute__ ((preserve_none));
>
> __attribute__ ((preserve_none)) void
> caller (long a, long b, long c, long d, long e, long f, long g)
> {
> __attribute__ ((aligned (32))) long x[4]; // for stack alignment
> ext (a, b, c, d, e, f, g, x);
> __attribute__ ((musttail)) return tail (a + b, b + c);
> }
>
> Insider caller, default_function_abi is the preserve_none ABI.
No, default_function_abi is always ARM_PCS_AAPCS64, even when compiling caller.
That's my point. The default ABI is fixed. It doesn't vary from one function
to another.
When compiling caller:
- default_function_abi is ARM_PCS_AAPCS64
- crtl->abi is ARM_PCS_PRESERVE_NONE
- ext is ARM_PCS_AAPCS64
Calling aarch64_conditional_register_usage always sets up call_used_regs for
ARM_PCS_AAPCS64, regardless of when it is called.
