On 1/25/16 05:27, Al Viro wrote:
>
> Again, do you have _any_ evidence of improved code generation with that
> patch? Because if you do, I would really like to see it, so I could file
> bugs against gcc optimizer.
>
> Your impression of what _Bool is and what semantics does it have appears
> to be rather different from that described in C99, but that's a secondary
> issue - first and foremost, on which .config and with which gcc version
> do you see improvements from that change?
>
For our case, the check_mount function have smaller size under x86_64
(movl for int, movb for bool, movl is longer than movb).
The related objdump is below, welcome any ideas, suggestions, and
discussions for it.
origin (for int):
00000000 <check_mount>:
0: 8b 12 mov (%edx),%edx
2: 81 e2 00 00 01 00 and $0x10000,%edx
8: 74 16 je 20 <check_mount+0x20>
a: c7 00 01 00 00 00 movl $0x1,(%eax)
10: b8 01 00 00 00 mov $0x1,%eax
15: c3 ret
16: 8d 76 00 lea 0x0(%esi),%esi
19: 8d bc 27 00 00 00 00 lea 0x0(%edi,%eiz,1),%edi
20: 31 c0 xor %eax,%eax
22: c3 ret
23: 8d b6 00 00 00 00 lea 0x0(%esi),%esi
29: 8d bc 27 00 00 00 00 lea 0x0(%edi,%eiz,1),%edi
new (for bool):
00000000 <check_mount>:
0: 8b 12 mov (%edx),%edx
2: 81 e2 00 00 01 00 and $0x10000,%edx
8: 74 0e je 18 <check_mount+0x18>
a: c6 00 01 movb $0x1,(%eax)
d: b8 01 00 00 00 mov $0x1,%eax
12: c3 ret
13: 90 nop
14: 8d 74 26 00 lea 0x0(%esi,%eiz,1),%esi
18: 31 c0 xor %eax,%eax
1a: c3 ret
1b: 90 nop
1c: 8d 74 26 00 lea 0x0(%esi,%eiz,1),%esi
[root@localhost fs]# gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/local/libexec/gcc/x86_64-pc-linux-gnu/6.0.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: ../gcc-ana/configure
Thread model: posix
gcc version 6.0.0 20151121 (experimental) (GCC)
--
Chen Gang (陈刚)
Open, share, and attitude like air, water, and life which God blessed
