On 03/02/2018 12:45 PM, Peter Bergner wrote:
> While debugging the PR84264 ICE caused by the following test case:
>
> void _setjmp ();
> void a (unsigned long *);
> void
> b ()
> {
> for (;;)
> {
> _setjmp ();
> unsigned long args[9]{};
> a (args);
> }
> }
>
> I noticed that IRA is spilling all pseudos that are live across the call
> to setjmp. Why is that? Trying to look through the history of this, I see
> Jim committed a patch to reload that removed it spilling everything across
> all setjmps:
>
> https://gcc.gnu.org/ml/gcc-patches/2003-11/msg01667.html
>
> But currently ira-lives.c:process_bb_node_lives() has:
>
> /* Don't allocate allocnos that cross setjmps or any
> call, if this function receives a nonlocal
> goto. */
> if (cfun->has_nonlocal_label
> || find_reg_note (insn, REG_SETJMP,
> NULL_RTX) != NULL_RTX)
> {
> SET_HARD_REG_SET (OBJECT_CONFLICT_HARD_REGS (obj));
> SET_HARD_REG_SET (OBJECT_TOTAL_CONFLICT_HARD_REGS (obj));
> }
>
> ...which forces us to spill everything live across the setjmp by forcing
> the pseudos to interfere all hardregs. That can't be good for performance.
> What am I missing?
You might want to hold off a bit. I've got changes for 21161 which can
help this significantly. Basically the live-across-setjmp set is way
too conservative -- it includes everything live at the setjmp, but it
really just needs what's live on the longjump path.
As for why, I believe it's related to trying to make sure everything has
the right values if we perform a longjmp.
I'll can include testing 84264 to see if my work helps there.
jeff
