https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101920
Bug ID: 101920
Summary: memcpy expansion treats unknown pointers as unaligned
Product: gcc
Version: 11.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: middle-end
Assignee: unassigned at gcc dot gnu.org
Reporter: dragan.mladjenovic at syrmia dot com
Target Milestone: ---
I guess it is easiest to observe this on Aarch64 with the following code:
#include <string.h>
void test (int *dst, int *src)
{
(void)memcpy (dst, src, sizeof *src);
}
With -O1 -mno-strict-align we get:
ldr w1, [x1]
str w1, [x0]
ret
With -O1 -mstrict-align we get:
ldrb w2, [x1]
strb w2, [x0]
ldrb w2, [x1, 1]
strb w2, [x0, 1]
ldrb w2, [x1, 2]
strb w2, [x0, 2]
ldrb w1, [x1, 3]
strb w1, [x0, 3]
ret
Or with Os:
mov x2, 4
b memcpy
It seems that builtins.c:get_pointer_alignment finds empty SSA_NAME_PTR_INFO
for both pointers and defaults to 8-bit alignment. This can be worked around by
applying __builtin_assume_alligned to both src and dest.
