https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96562
Bug ID: 96562
Summary: Rather poor assembly generated for
copy-list-initialization in return statement.
Product: gcc
Version: 10.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: maxim.yegorushkin at gmail dot com
Target Milestone: ---
Rather poor assembly generated for trivial code.
The following code:
template<class P, class SizeT>
struct Span {
P begin_;
SizeT size_;
};
Span<char*, unsigned> f(char* p, char* q) {
return {p, static_cast<unsigned>(q - p)};
}
When compiled with gcc-6.1 to gcc-10.2 with options "-O3 -march=skylake
-mtune=skylake" produces unexpectedly long and sub-optimal assembly code:
f(unsigned char*, unsigned char*):
mov QWORD PTR [rsp-16], 0
mov QWORD PTR [rsp-24], rdi
sub rsi, rdi
vmovdqa xmm1, XMMWORD PTR [rsp-24]
vpinsrd xmm0, xmm1, esi, 2
vmovdqa XMMWORD PTR [rsp-24], xmm0
mov rax, QWORD PTR [rsp-24]
mov rdx, QWORD PTR [rsp-16]
ret
clang with the same options produces the expected assembly:
f(unsigned char*, unsigned char*):
mov rdx, rsi
mov rax, rdi
sub edx, eax
ret
Is there a way to make gcc produce the expected assembly, please?
https://gcc.godbolt.org/z/bacGW8
