https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70308
Bug ID: 70308
Summary: memset generates rep stosl instead of rep stosq
Product: gcc
Version: 5.2.1
Status: UNCONFIRMED
Severity: minor
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: socketpair at gmail dot com
Target Milestone: ---
Consider this program:
=============================
#include <string.h>
#include <stdio.h>
#include <unistd.h>
int main() {
char buf[128];
if (scanf("%s", buf) != 1) return 42;
memset(buf,0, 128);
asm volatile("": : :"memory");
return 0;
}
==============================
compile with -O3
and you will see, that memset is translated to "rep stosl". good.
Next, comment line with scanf() and compile again
and you will see, that memset is translated to "rep stosq", which is much
faster.
So, I consider that gcc should emit "rep stosq" in both cases.
