https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77270
nightstrike <nightstrike at gmail dot com> changed:
What |Removed |Added
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Keywords| |wrong-code
--- Comment #1 from nightstrike <nightstrike at gmail dot com> ---
This should trigger the prefetchw instruction with -march=k8 -O3:
void f() {
extern int size;
int i;
float * fvec;
float * fptr = (float *) get();
for(i = 0; i < size; ++i)
fvec[i] = fptr[i];
int * ivec;
int * iptr = (int *) get();
for(i = 0; i < size; ++i)
ivec[i] = iptr[i];
}
If I give an "extern void * get()" prototype for get, if there's only one
vector loop, or if size is local, the prefetchw instruction goes away.
$ gcc -fverbose-asm -S a.c -march=k8 -O3; grep prefetchw a.s
prefetchw 464(%rcx) #
prefetchw (%rdx) # ivtmp.37
