https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109667
--- Comment #8 from Paweł Bylica <chfast at gmail dot com> ---
Since GCC 15 the testcase is even worse because of a different change,
r15-3328-g673a448aa24efedd5ac140ebf7bfe652d7a6a846 (clearing of small padded
objects in gimplify_init_constructor). The return {d, carryout != 0}; now
clears the whole R first, so the padding after carry is kept in memory.
GCC 14.2 (7 instructions):
cmp rdi, rsi
setb al
movzx eax, al
add al, -1
sbb rdi, rsi
setc al
ret
GCC 15.2 and trunk (14 instructions):
cmp rdi, rsi
mov DWORD PTR [rsp-40], 0
movabs rax, 72057594037927935
setb cl
mov DWORD PTR [rsp-37], 0
and rax, QWORD PTR [rsp-40]
sal rax, 8
mov rdx, rax
mov dl, cl
mov rax, rdx
add al, -1
sbb rdi, rsi
setc al
ret
I filed it separately as PR 127699.
