https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106475
Bug ID: 106475
Summary: Loop vectorizer prevents vectorization
Product: gcc
Version: 13.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: christophm30 at gmail dot com
Target Milestone: ---
Inspired by https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106352 I've tested
GCC's behaviour after adding the restrict keyword as advised there.
This results in the following code:
```
#include <inttypes.h>
void
foo (uint8_t *restrict dst, int i_dst_stride,
uint8_t *src1, int i_src1_stride,
uint8_t *src2, int i_src2_stride,
int i_height)
{
for (int y = 0; y < i_height; y++)
{
for( int x = 0; x < 8; x++ )
dst[x] = (src1[x] + src2[x] + 1);
dst += i_dst_stride;
src1 += i_src1_stride;
src2 += i_src2_stride;
}
}
```
The issue is now, that this only gets vectorized, if we pass
`-O3 -fno-tree-loop-vectorize`, i.e. disable the loop vectorizer.
Obviously, what helps for this function is not necessarily beneficial
for the rest of the program. So a solution that does not need to disable
the loop vectorization to generate faster code would be preferred.
I have not found a GCC version that can do this, so this is not a
regression, but a limitation. I also have not found a similar ticket,
but I suspect this to be somehow a known issue.
Are there any ideas to improve this?
