https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111657
Bug ID: 111657
Summary: Memory copy with structure assignment from named
address space is not working
Product: gcc
Version: 12.3.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: middle-end
Assignee: unassigned at gcc dot gnu.org
Reporter: ubizjak at gmail dot com
Target Milestone: ---
Taken from [1]. Compile the following testcase with -O2 -mno-sse:
--cut here--
struct a
{
long arr[30];
};
__seg_gs struct a m;
void
foo (struct a *dst)
{
*dst = m;
}
--cut here--
the produced assembly:
foo:
.LFB0:
xorl %eax, %eax
cmpq $240, %rax
jnb .L5
.L2:
movzbl %gs:m(%rax), %edx
movb %dl, (%rdi,%rax)
addq $1, %rax
cmpq $240, %rax
jb .L2
.L5:
ret
As rightfully said in [1]:
"...and look at the end result. It's complete and utter sh*t:
<...>
to the point that I can only go "WTF"?
I mean, it's not just that it does the copy one byte at a time. It
literally compares %rax to $240 just after it has cleared it. I look
at that code, and I go "a five-year old with a crayon could have done
better".
[1]
https://lore.kernel.org/lkml/CAHk-=wh+cfn58xxmlng6dh+eb9-2dyfabxjf2ftsz+vfqvv...@mail.gmail.com/
