[Bug tree-optimization/28524] New: x*x in a loop folded to powf(x,2.) which prevents vectorization

[fxcoudert at gcc dot gnu dot org]

$ cat a.c
void foo (float * restrict x, float * restrict y)
{
  int i;
  for (i = 0; i < 10000; i++)
    x[i] = y[i] * y[i];
}
$ gcc a.c -O1 -ffast-math -msse -mfpmath=sse -ftree-vectorize
-ftree-vectorizer-verbose=5 -std=c99 -c

a.c:5: note: Alignment of access forced using peeling.
a.c:5: note: Vectorizing an unaligned access.
a.c:5: note: not vectorized: relevant stmt not supported: D.1353_14 =
__builtin_powf (D.1352_13, 2.0e+0)
a.c:5: note: vectorized 0 loops in function.


I find in fold-const.c:fold_binary, around line 9091, I found the following:
         /* Optimize x*x as pow(x,2.0), which is expanded as x*x.  */


-- 
           Summary: x*x in a loop folded to powf(x,2.) which prevents
                    vectorization
           Product: gcc
           Version: 4.2.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: normal
          Priority: P3
         Component: tree-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: fxcoudert at gcc dot gnu dot org
 GCC build triplet: i686-pc-linux-gnu
  GCC host triplet: i686-pc-linux-gnu
GCC target triplet: i686-pc-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28524