Messages in this thread |  | | | From | Denis Vlasenko <> | | Subject | Re: Some functions are not inlined by gcc 3.2, resulting code is ugly | | Date | Sun, 3 Nov 2002 22:17:13 -0200 |
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On 3 November 2002 14:17, Jussi Laako wrote: > On Sun, 2002-11-03 at 18:17, Denis Vlasenko wrote: > > Jump target 17e0 is aligned (with nops): > > 17dd: 88 02 mov %al,(%edx) > > 17df: 90 nop > > 17e0: 89 d0 mov %edx,%eax > > 17e2: 5a pop %edx > > > > 17ec: eb f2 jmp 17e0 > > <__constant_memcpy+0x20> > > > > 17fa: eb e4 jmp 17e0 > > <__constant_memcpy+0x20> > > > > 1800: eb de jmp 17e0 > > <__constant_memcpy+0x20> > > > > 187c: e9 5f ff ff ff jmp 17e0 > > <__constant_memcpy+0x20> 1881: eb 0d jmp 1890 > > <__constant_memcpy+0xd0> 1883: 90 nop > > ... > > > 188f: 90 nop > > 1890: c1 e9 02 shr $0x2,%ecx > > 1893: 89 d7 mov %edx,%edi > > And also jump target 1890 is aligned. > > > I think the penalty of few NOPs is smaller than result of jump to > unaligned address. This is especially true with P4 architecture.
Alignment does not eliminate jump. It only moves jump target to 16 byte boundary. This _probably_ makes execution slightly faster but on average it costs you 7,5 bytes. This price is too high when you take into account L1 instruction cache wastage and current bus/core clock ratios. -- vda - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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