https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68480
Bug ID: 68480
Summary: strict-aliasing not respected
Product: gcc
Version: 4.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: manjeetdahiya at gmail dot com
Target Milestone: ---
When I compile following code with -O2 -m32 -S -fno-strict-aliasing
-fno-unrolling -fno-builtin. GCC seems to be not respecting
-fno-strict-aliasing. I don't encounter this issue in gcc-4.8.
struct list { int hd; struct list * tl; };
struct list * reverselist (struct list * l)
{
struct list * r, * r2;
for (r = NULL; l != NULL; l = l->tl) {
r2 = mymalloc(sizeof(struct list));
r2->hd = l->hd;
r2->tl = r;
r = r2;
}
return r;
}
The issue is that statement A precedes B. It is fine in gcc-4.8.4.
Assembly gcc-4.1.0:
movl (%ebx), %eax # <variable>.hd, <variable>.hd
movl %esi, 4(%edx) # r, <variable>.tl
movl %edx, %esi # D.3244, r
A: movl 4(%ebx), %ebx # <variable>.tl, l
B: movl %eax, (%edx) # <variable>.hd, <variable>.hd
testl %ebx, %ebx # l
Assembly gcc-4.8.4:
movl (%ebx), %edx # l_16->hd, D.5537
movl %esi, 4(%eax) # r, r_7->tl
movl %edx, (%eax) # D.5537, r_7->hd
movl 4(%ebx), %ebx # l_16->tl, l
testl %ebx, %ebx # l
