[Bug tree-optimization/36493] New: [4.3/4.4 Regression] vectorizer aliasing bug

["jsm28 at gcc dot gnu dot org" <gcc-bugzilla@gcc.gnu.org>]

The following code aborts if built for i686-pc-linux-gnu with -msse2 -O3.

extern void abort (void);
int
main (void)
{
  int i;
  long x[12] __attribute__((aligned(16)));
  x[0] = 1;
  for (i = 0; i < 12; i++)
    x[i] = i;
  if (x[0] != 0)
    abort ();
  return 0;
}

The loop gets vectorized using "vector int *" pointers, and then the compiler
decides that "vector int" writes don't conflict with "long" reads.  (If an
array of int is used instead, the test passes.)

(Not x86-specific; originally observed as a failure of
gcc.c-torture/execute/loop-13.c on SPE with an unsubmitted patch to support
autovectorization there.)


-- 
           Summary: [4.3/4.4 Regression] vectorizer aliasing bug
           Product: gcc
           Version: 4.4.0
            Status: UNCONFIRMED
          Keywords: wrong-code
          Severity: normal
          Priority: P3
         Component: tree-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: jsm28 at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36493