From d82f29cd593e371acb3a6f11656543cf2e6e2421 Mon Sep 17 00:00:00 2001 From: Denys Vlasenko Date: Tue, 6 Apr 2010 05:29:26 +0200 Subject: 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 --- libc/sysdeps/linux/i386/bits/syscalls.h | 15 +++++++++++---- 1 file changed, 11 insertions(+), 4 deletions(-) (limited to 'libc/sysdeps/linux') 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) \ -- cgit v1.2.3