https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80491
--- Comment #2 from Victor Khimenko <khim at google dot com> ---
An interesting observation: -O1 actually produces perfect code:
$ gcc -S -O1 test.cc -o-
.file "test.cc"
.text
.p2align 4,,15
.globl _Z3addR4pairS0_
.type _Z3addR4pairS0_, @function
_Z3addR4pairS0_:
.LFB4:
.cfi_startproc
movq (%rdi), %rax
movq 8(%rsi), %rdx
addq (%rsi), %rax
adcq 8(%rdi), %rdx
ret
.cfi_endproc
.LFE4:
.size _Z3addR4pairS0_, .-_Z3addR4pairS0_
.ident "GCC: (GNU) 7.0.1 20170307 (experimental)"
.section .note.GNU-stack,"",@progbits
For some reason incrased optimization levels make code significantly worse
here.
