[PATCH] combine: Handle aborts in is_parallel_of_n_reg_sets (PR68381)
Segher Boessenkool
segher@kernel.crashing.org
Tue Nov 24 07:13:00 GMT 2015
Some users of is_parallel_of_n_reg_sets disregard the clobbers in a
parallel after it has returned "yes, this is a parallel of N sets and
maybe some clobbers". But combine uses a clobber of const0_rtx to
indicate substitution failure, so this leads to disaster.
Fix this by checking for such special clobbers in is_parallel_of_n_reg_sets.
Tested on powerpc64-linux. Also tested with Kyrill's testcase, manually
inspected the generated asm and the combine dump file (with some extra
instrumentation). This testcase needs -O1 btw.
The "performance problem" in the PR (same testcase, but with -O3) is
a missed jump optimization: a pseudo is set (to 0) in one BB (and
nowhere else), and then tested against 0 in another BB. Nothing after
combine seems to handle this.
Applying this patch to trunk. Kyrill, could you handle the testcase?
Together with whatever you decide should be done for the -O3 problem.
Thank you for tracking down this nastiness!
Segher
2015-11-24 Segher Boessenkool <segher@kernel.crashing.org>
PR rtl-optimization/68381
* combine.c (is_parallel_of_n_reg_sets): Return false if the pattern
is poisoned.
---
gcc/combine.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/gcc/combine.c b/gcc/combine.c
index 2a66fd5..4958d3b 100644
--- a/gcc/combine.c
+++ b/gcc/combine.c
@@ -2512,7 +2512,8 @@ is_parallel_of_n_reg_sets (rtx pat, int n)
|| !REG_P (SET_DEST (XVECEXP (pat, 0, i))))
return false;
for ( ; i < len; i++)
- if (GET_CODE (XVECEXP (pat, 0, i)) != CLOBBER)
+ if (GET_CODE (XVECEXP (pat, 0, i)) != CLOBBER
+ || XEXP (XVECEXP (pat, 0, i), 0) == const0_rtx)
return false;
return true;
--
1.9.3
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