Re: [PATCH 03/11] aarch64: Use br instead of ret for eh_return

[Richard Sandiford <richard.sandiford@arm.com>]

Richard Sandiford <richard.sandiford@arm.com> writes:
> Rather than hiding this in target code, perhaps we should add a
> target-independent concept of an "eh_return taken" flag, say
> EH_RETURN_TAKEN_RTX.
>
> We could define it so that, on targets that define EH_RETURN_TAKEN_RTX,
> a register EH_RETURN_STACKADJ_RTX and a register EH_RETURN_HANDLER_RTX
> are only meaningful when the flag is true.  E.g. we could have:
>
> #ifdef EH_RETURN_HANDLER_RTX

Gah, I meant #ifdef EH_RETURN_TAKEN_RTX here

>   for (rtx tmp : { EH_RETURN_STACKADJ_RTX, EH_RETURN_HANDLER_RTX })
>     if (tmp && REG_P (tmp))
>       emit_clobber (tmp);
> #endif
>
> in the "normal return" part of expand_eh_return.  (If some other target
> wants a flag with different semantics, it'd be up to them to add it.)
>
> That should avoid most of the bad code-quality effects, since the
> specialness of x4-x6 will be confined to the code immediately before
> the pre-epilogue exit edges.
>
> Thanks,
> Richard