https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65236
--- Comment #3 from Martin Liška <marxin at gcc dot gnu.org> ---
There's generated assembly:
000000000045faa0
<_ZNK6google8protobuf11MessageLite24SerializePartialAsStringEv>:
45faa0: 53 push %rbx
45faa1: 48 89 fb mov %rdi,%rbx
45faa4: 48 89 f7 mov %rsi,%rdi
45faa7: 48 8d 43 10 lea 0x10(%rbx),%rax
45faab: 48 c7 43 08 00 00 00 movq $0x0,0x8(%rbx)
45fab2: 00
45fab3: c6 43 10 00 movb $0x0,0x10(%rbx)
45fab7: 48 89 de mov %rbx,%rsi
45faba: 48 89 03 mov %rax,(%rbx)
45fabd: e8 0e ff ff ff callq 45f9d0
<_ZNK6google8protobuf11MessageLite21AppendPartialToStringEPNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEE>
45fac2: 84 c0 test %al,%al
45fac4: 75 0e jne 45fad4
<_ZNK6google8protobuf11MessageLite24SerializePartialAsStringEv+0x34>
45fac6: 48 8b 03 mov (%rbx),%rax
45fac9: 48 c7 43 08 00 00 00 movq $0x0,0x8(%rbx)
45fad0: 00
45fad1: c6 00 00 movb $0x0,(%rax)
45fad4: 48 89 d8 mov %rbx,%rax
45fad7: 5b pop %rbx
45fad8: c3 retq
45fad9: 00 00 add %al,(%rax)
45fadb: 00 00 add %al,(%rax)
45fadd: 00 00 add %al,(%rax)
...
000000000045fae0 <_ZNK6google8protobuf11MessageLite17SerializeAsStringEv>:
45fae0: 53 push %rbx
45fae1: 48 89 fb mov %rdi,%rbx
45fae4: 48 83 ec 20 sub $0x20,%rsp
45fae8: 48 89 e7 mov %rsp,%rdi
45faeb: e8 b0 ff ff ff callq 45faa0
<_ZNK6google8protobuf11MessageLite24SerializePartialAsStringEv>
45faf0: 48 8b 04 24 mov (%rsp),%rax
(marker)
----------------------------------------------------------------------vvvv
45faf4: 48 89 03 mov %rax,(%rbx)
45faf7: 48 8b 44 24 08 mov 0x8(%rsp),%rax
45fafc: 48 89 43 08 mov %rax,0x8(%rbx)
45fb00: 48 8b 44 24 10 mov 0x10(%rsp),%rax
45fb05: 48 89 43 10 mov %rax,0x10(%rbx)
45fb09: 48 8b 44 24 18 mov 0x18(%rsp),%rax
45fb0e: 48 89 43 18 mov %rax,0x18(%rbx)
45fb12: 48 83 c4 20 add $0x20,%rsp
45fb16: 48 89 d8 mov %rbx,%rax
45fb19: 5b pop %rbx
45fb1a: c3 retq
45fb1b: 00 00 add %al,(%rax)
45fb1d: 00 00 add %al,(%rax)
Where I suspect a stack load/store instruction after returning from the call
------^^^^
