diff options
| author | Denys Vlasenko <vda.linux@googlemail.com> | 2010-04-06 05:29:26 +0200 |
|---|---|---|
| committer | Denys Vlasenko <vda.linux@googlemail.com> | 2010-04-06 05:29:26 +0200 |
| commit | d82f29cd593e371acb3a6f11656543cf2e6e2421 (patch) | |
| tree | 433df3e8a590282fa9cbc80409412d755b8b834c /libc/sysdeps | |
| parent | eefaf06888e3dcbc410b4cc2d231035f4400c7ac (diff) | |
i386/bits/syscalls.h: generate better code using more restrictive asm constraints
Example: time() doesn't push/pop two registers now, and is smaller:
<__GI_time>:
-57 push %edi
-8b 7c 24 08 mov 0x8(%esp),%edi
-53 push %ebx
-89 fb mov %edi,%ebx
+8b 4c 24 04 mov 0x4(%esp),%ecx
+87 cb xchg %ecx,%ebx
b8 0d 00 00 00 mov $0xd,%eax
cd 80 int $0x80
-5b pop %ebx
-5f pop %edi
+87 cb xchg %ecx,%ebx
c3 ret
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
Diffstat (limited to 'libc/sysdeps')
| -rw-r--r-- | libc/sysdeps/linux/i386/bits/syscalls.h | 15 |
1 files changed, 11 insertions, 4 deletions
diff --git a/libc/sysdeps/linux/i386/bits/syscalls.h b/libc/sysdeps/linux/i386/bits/syscalls.h index 46c2d9962..a6e26d7ec 100644 --- a/libc/sysdeps/linux/i386/bits/syscalls.h +++ b/libc/sysdeps/linux/i386/bits/syscalls.h @@ -141,14 +141,21 @@ __asm__ ( #define RESTOREARGS_6 "pop %%ebp\n\t" RESTOREARGS_1 #define ASMFMT_0() +/* "acdSD" constraint would work too, but "SD" would use esi/edi and cause + * them to be pushed/popped by compiler, "a" would use eax and cause ebx + * to be saved/restored on stack, not in register. Narrowing choice down + * to "ecx or edx" results in smaller and faster code: */ #define ASMFMT_1(arg1) \ - , "acdSD" (arg1) + , "cd" (arg1) +/* Can use "adSD" constraint here: */ #define ASMFMT_2(arg1, arg2) \ - , "adSD" (arg1), "c" (arg2) + , "d" (arg1), "c" (arg2) +/* Can use "aSD" constraint here: */ #define ASMFMT_3(arg1, arg2, arg3) \ - , "aSD" (arg1), "c" (arg2), "d" (arg3) + , "a" (arg1), "c" (arg2), "d" (arg3) +/* Can use "aD" constraint here: */ #define ASMFMT_4(arg1, arg2, arg3, arg4) \ - , "aD" (arg1), "c" (arg2), "d" (arg3), "S" (arg4) + , "a" (arg1), "c" (arg2), "d" (arg3), "S" (arg4) #define ASMFMT_5(arg1, arg2, arg3, arg4, arg5) \ , "a" (arg1), "c" (arg2), "d" (arg3), "S" (arg4), "D" (arg5) #define ASMFMT_6(arg1, arg2, arg3, arg4, arg5, arg6) \ |