https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69570
Jakub Jelinek <jakub at gcc dot gnu.org> changed:
What |Removed |Added
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CC| |uros at gcc dot gnu.org
--- Comment #1 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
I guess ifcvt only triggers some latent bug, either RA or more likely in
reg-stack. That said, all the comments about the r229822 changes say its
purpose is to handle multiple sets in the conditional block, but clearly the
patch as implemented considers one set to be also multiple sets. The problem
with that is that it handles it worse than the code later on in ifcvt - it uses
temporaries and hopes later passes get rid of those temporaries, but they
actually affect the register allocation.
By restricting the ifcvt multiple sets coversion to actually multiple sets
like:
--- gcc/ifcvt.c.jj 2016-01-21 17:53:32.000000000 +0100
+++ gcc/ifcvt.c 2016-01-31 13:47:34.171323086 +0100
@@ -3295,7 +3295,7 @@ bb_ok_for_noce_convert_multiple_sets (ba
if (count > limit)
return false;
- return count > 0;
+ return count > 1;
}
/* Given a simple IF-THEN-JOIN or IF-THEN-ELSE-JOIN block, attempt to convert
the test passes again, after ifcvt there are no additional unneeded temporaries
and e.g. postreload dump contains 5 fewer instruction, and has fewer
spills/fills. Of course we really need to figure out what the bug actually is,
but unless there is some strong reason (which should be documented), IMHO the
above patch is right too.
