chf...@pathscale:~/gcc$ cat foo.c
float a[100][100], b[100][100];
void foo(int n)
{
int i, j;
for(j=0; j<n; j++)
for(i=0; i< n; i++)
a[i][j] = a[i][j] + b[i][j];
}
chf...@pathscale:~/gcc$ gcc -O3 -ftree-vectorizer-verbose=2 -c foo.c
foo.c:6: note: not vectorized: can't create epilog loop 2.
foo.c:7: note: not vectorized: complicated access pattern.
foo.c:3: note: vectorized 0 loops in function.
Information from open64:
chf...@pathscale:~/gcc$ opencc -O3 -LNO:simd_verbose=on -c foo.c
(foo.c:0) LOOP WAS VECTORIZED.
(foo.c:0) LOOP WAS VECTORIZED.
chf...@pathscale:~/gcc$ opencc -O3 -LNO:simd_verbose=on:interchange=0 -c foo.c
(foo.c:0) Non-contiguous array "a" reference exists. Loop was not vectorized.
(foo.c:0) Non-contiguous array "a" reference exists. Loop was not vectorized.
Graphite may be able to do this basic loop interchange.
--
Summary: The loop is not interchanged and thus could not be
vectorized.
Product: gcc
Version: 4.5.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: changpeng dot fang at amd dot com
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43427
