------- Comment #4 from jhaberman at gmail dot com 2010-07-10 01:38 -------
This seems to happen even with POD return types:
int foo();
void bar(int a);
void func() {
bar(foo());
}
In 32-bit mode it spills the return value to the stack for no reason. It also
seems to overallocate the stack (28 bytes allocated, only 4 used):
00000000 <func>:
0: 83 ec 1c sub esp,0x1c
3: e8 fc ff ff ff call 4 <func+0x4>
4: R_386_PC32 foo
8: 89 04 24 mov DWORD PTR [esp],eax
b: e8 fc ff ff ff call c <func+0xc>
c: R_386_PC32 bar
10: 83 c4 1c add esp,0x1c
13: c3 ret
In 64-bit mode there is no store, but it *does* allocate 8 bytes of stack that
it never uses:
0000000000000000 <func>:
0: 48 83 ec 08 sub rsp,0x8
4: 31 c0 xor eax,eax
6: e8 00 00 00 00 call b <func+0xb>
7: R_X86_64_PC32 foo+0xfffffffffffffffc
b: 48 83 c4 08 add rsp,0x8
f: 89 c7 mov edi,eax
11: e9 00 00 00 00 jmp 16 <func+0x16>
12: R_X86_64_PC32 bar+0xfffffffffffffffc
Any idea how hard this bug is to fix?
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44194
