On 24/11/15 06:37, Segher Boessenkool wrote:
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!
Sure, here's the testcase with the "-O" in the dg-options I had left out.
Applying to trunk.
For the performance issue I'll investigate a bit further.
Thanks,
Kyrill
2015-11-24 Kyrylo Tkachov <kyrylo.tkac...@arm.com>
PR rtl-optimization/68381
* gcc.c-torture/execute/pr68381.c: New test.
Segher
2015-11-24 Segher Boessenkool <seg...@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;
commit e5ab9ee234cb7f4b25e5aa56e64cf3a8a0e56f58
Author: Kyrylo Tkachov <kyrylo.tkac...@arm.com>
Date: Tue Nov 17 15:33:58 2015 +0000
[combine] PR rtl-optimization/68381: Only restrict pure simplification in mult-extend subst case, allow other substitutions
diff --git a/gcc/testsuite/gcc.c-torture/execute/pr68381.c b/gcc/testsuite/gcc.c-torture/execute/pr68381.c
new file mode 100644
index 0000000..cb6abcb
--- /dev/null
+++ b/gcc/testsuite/gcc.c-torture/execute/pr68381.c
@@ -0,0 +1,22 @@
+/* { dg-options "-O -fexpensive-optimizations -fno-tree-bit-ccp" } */
+
+__attribute__ ((noinline, noclone))
+int
+foo (unsigned short x, unsigned short y)
+{
+ int r;
+ if (__builtin_mul_overflow (x, y, &r))
+ __builtin_abort ();
+ return r;
+}
+
+int
+main (void)
+{
+ int x = 1;
+ int y = 2;
+ if (foo (x, y) != x * y)
+ __builtin_abort ();
+ return 0;
+}
+
