https://gcc.gnu.org/bugzilla/show_bug.cgi?id=120689
Bug ID: 120689
Summary: Codegen optimization regression passing struct in
register in gcc 10+ on x86-64.
Product: gcc
Version: 12.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: amohr at amohr dot org
Target Milestone: ---
struct s { char a, b, c; };
void t2(s);
void t1(s x) {
t2(x);
}
GCC 9.5 on x86-64 at -O3 generates:
t1(s):
jmp t2(s)
GCC 10.1 (and newer) at -O3 generates:
t1(s):
mov edx, edi
mov eax, edi
movzx edi, dil
shr eax, 16
and edx, 65280
or rdx, rdi
movzx edi, al
sal rdi, 16
or rdi, rdx
jmp t2(s)
I tested all newer major versions thru 15 & trunk, and they do similarly.
