[PATCH][IRA,LRA] Fix PR87466, all pseudos live across setjmp are spilled

[Segher Boessenkool]

Hi Peter,

On Fri, Sep 28, 2018 at 10:12:02PM -0500, Peter Bergner wrote:
> Currently, both IRA and LRA spill all pseudo regs that are live across a
> setjmp call.  If the target has a sane setjmp, then the compiler should not
> have to treat the setjmp call any differently than is does any other normal
> function call.  Namely, just mark all pseudos that are live across the setjmp
> as conflicting with the volatile registers.
> 
> This issue was discussed in the following gcc mailing list thread:
> 
>   https://gcc.gnu.org/ml/gcc/2018-03/msg00014.html
> 
> ...and some people mentioned that some systems do not have sane setjmp
> implementations and therefore need the spill all pseudos live across setjmps
> to get correct functionality.  It was decided in the thread above that we
> should create a target hook that can allow targets to tell IRA and LRA
> whether or not they have a sane setjmp implementation.  The following patch
> implements that idea along with converting the rs6000 port to use the hook.

> +bool
> +default_is_reg_clobbering_setjmp_p (const rtx_insn *insn)
> +{
> +  return CALL_P (insn)
> +	 && find_reg_note (insn, REG_SETJMP, NULL_RTX) != NULL_RTX;
> +}

Since all implementations of this hook will have to do the same, I think
it is better if you leave this test at the (only two) callers.  The hook
doesn't need an argument then, and maybe is better named something like
setjmp_is_normal_call?  (The original code did not test CALL_P btw).

(Whatever you end up with, the rs6000 part is of course pre-approved).


Segher