https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101993
--- Comment #2 from Hongyu Wang <wwwhhhyyy333 at gmail dot com> ---
(In reply to Richard Biener from comment #1)
> We can vectorize this with masked moves when using AVX2. clang seems to
> simply remove the test completely - C seems to guarantee that a + i is a
> valid pointer
> if any of a + i is accessed and thus a + i is never NULL.
>
> But then - just don't write such stupid checks? What real-world code was
> this testcase created from?
It came from 538.imagick_r
---
#define GetPixelIndex(indexes) \
((indexes == (const unsigned short *) NULL) ? 0 : (*(indexes)))
for (v=0; v < (ssize_t) kernel->height; v++) {
for (u=0; u < (ssize_t) kernel->width; u++, k--) {
if ( IsNaN(*k) ) continue;
result.red += (*k)*k_pixels[u].red;
result.green += (*k)*k_pixels[u].green;
result.blue += (*k)*k_pixels[u].blue;
result.opacity += (*k)*k_pixels[u].opacity;
if ( image->colorspace == CMYKColorspace)
result.index += (*k)*GetPixelIndex(k_indexes+u);
}
k_pixels += virt_width;
k_indexes += virt_width;
}
---
I extracted it to a small test in https://godbolt.org/z/G5h6nWvb5
which can be vectorized by clang but not gcc due to such pattern.
>
> There is currently no optimization phase that would use loop info to elide
> NULL pointer checks and I'm not sure where I'd put such. Note the argument
> for
> GCC would be that the access *(a + i) infers that a + i does not "overflow"
> to another object (including NULL). That's sth the points-to solver would
> assume here (but the points-to solver is bad at tracking NULL).
