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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug middle-end/96326] [10/11 Regression] Incorrect loop
 optimization at -O3 since r10-4803-g8489e1f45b50600c
Date: Mon, 27 Jul 2020 07:43:01 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D96326

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |INVALID
             Status|NEW                         |RESOLVED
   Target Milestone|---                         |10.3

--- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> ---
The following works - your unsigned long objects are not aligned according
to the type which makes the accesses undefined (actually C even specifies
forming the pointer itself is undefined).

#include <string.h>
#include <stdio.h>

typedef unsigned long mylong __attribute__((aligned(1)));
int main() {
        char buf[128];
        char *src =3D buf;
        char *op =3D buf + 3;
        int len =3D 64;
        strcpy(buf, "abc");
        while (op - src < 8) {
                *(mylong*)op =3D *(const mylong*)src;
                len -=3D op - src;
                op +=3D op - src;
        }
        while (len > 0) {
                *(mylong*)op =3D *(const mylong*)src;
                src +=3D 8;
                op +=3D 8;
                len -=3D 8;
        }
        printf("%ld\n", strlen(buf));
}=