https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102575
Bug ID: 102575
Summary: Failure to optimize double _Complex stores to use
largest loads/stores possible
Product: gcc
Version: 12.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: gabravier at gmail dot com
Target Milestone: ---
void test(double _Complex *a)
{
a[0] = 1;
a[1] = 1;
}
With -O3, on AMD64 GCC outputs this:
test(double _Complex*):
movsd xmm1, QWORD PTR .LC0[rip]
movsd xmm0, QWORD PTR .LC0[rip+8]
movsd QWORD PTR [rdi], xmm1
movsd QWORD PTR [rdi+8], xmm0
movsd QWORD PTR [rdi+16], xmm1
movsd QWORD PTR [rdi+24], xmm0
ret
Clang instead outputs this:
test(double _Complex*):
movsd xmm0, qword ptr [rip + .LCPI0_0] # xmm0 = mem[0],zero
movups xmmword ptr [rdi], xmm0
movups xmmword ptr [rdi + 16], xmm0
ret
It seems to me like the second output should always be faster.
PS: The difference is even larger with `-mavx2`.
