https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114061
Bug ID: 114061
Summary: GCC fails vectorization when using __builtin_prefetch
Product: gcc
Version: 14.0
Status: UNCONFIRMED
Keywords: missed-optimization
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: tnfchris at gcc dot gnu.org
Target Milestone: ---
The following example:
void foo(double * restrict a, double * restrict b, int n){
int i;
for(i=0; i<n; ++i){
a[i] = a[i] + b[i];
__builtin_prefetch(&(b[i+8]));
}
}
fails to vectorize because of the __builtin_prefetch.
/app/example.c:5:5: missed: statement clobbers memory: __builtin_prefetch
(_10);
/app/example.c:3:13: missed: not vectorized: loop contains function calls or
data references that cannot be analyzed
However two things:
1. prefetching are usually hints anyway and not a correctness thing. It should
be safe to elide the call and vectorizer as normal.
2. SVE has prefetched vector operations which we can use here. The vector
prefetches are also predicated so they need to be actually codegened.
Perhaps one solution here would be to have a vect-pattern which checks for
COND_PREFETCH support if supported, and if not just elides the prefetch?
