https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99856
Bug ID: 99856
Summary: Alpha Compositing auto vectorization regression: 8.3
-> 9.1
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: dushistov at mail dot ru
Target Milestone: ---
Such code vectorized with gcc 8.3, but failed to vectorized with 9.1.
Last version of clang works just fine.
```
#include <stdint.h>
#include <stddef.h>
#define SHIFTFORDIV255(a)\
((((a) >> 8) + a) >> 8)
#define DIV255(a)\
SHIFTFORDIV255(a + 0x80)
void
opSourceOver_premul(uint8_t* restrict Rrgba,
const uint8_t* restrict Srgba,
const uint8_t* restrict Drgba, size_t len)
{
size_t i = 0;
for (; i < len*4; i += 4) {
uint8_t Sa = Srgba[i + 3];
Rrgba[i + 0] = DIV255(Srgba[i + 0] * 255 + Drgba[i + 0] * (255 - Sa));
Rrgba[i + 1] = DIV255(Srgba[i + 1] * 255 + Drgba[i + 1] * (255 - Sa));
Rrgba[i + 2] = DIV255(Srgba[i + 2] * 255 + Drgba[i + 2] * (255 - Sa));
Rrgba[i + 3] = DIV255(Srgba[i + 3] * 255 + Drgba[i + 3] * (255 - Sa));
}
}
```
see https://godbolt.org/z/PW65xzb4h
with assembler output for 8.3 and 9.1
