On 05/09/12 13:02, Steven Bosscher wrote:
> On Wed, Sep 5, 2012 at 1:42 PM, Matthew Gretton-Dann wrote:
>> Whilst this fix works for this particular case I am not sure it is the
>> best fix for the general issue, and so if others have a better idea how
>> to fix this I would be very happy.
>
> postreload-gcse.c is broken in "interesting" ways. Look at this gem for
> example:
>
> static bool
> reg_changed_after_insn_p (rtx x, int cuid)
> {
> unsigned int regno, end_regno;
>
> regno = REGNO (x);
> end_regno = END_HARD_REGNO (x);
> do
> if (reg_avail_info[regno] > cuid)
> return true;
> while (++regno < end_regno);
> return false;
> }
>
> So the more conservative the fix, the better :-)
>
> The patch looks correct to me. But perhaps the pass should just punt
> on blocks not ending in a simple jump in
> bb_has_well_behaved_predecessors?
>
> Ciao!
> Steven
>
That sort of makes sense. Why would we ever want to hoist an insn out
of a cold block into a hot one? I could see it making sense to do the
reverse on occasion, but clearly care is needed here.
R.
