Messages in this thread | | | Date | Wed, 1 Nov 2000 01:27:42 +0100 (CET) | From | Ingo Molnar <> | Subject | Re: 2.2.18Pre Lan Performance Rocks! |
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On Tue, 31 Oct 2000, Jeff V. Merkey wrote:
> [...] These types of optimizations are possible when people have > acccess to Intel Red Cover documents, [...]
optimizing away AGIs has been documented by public Intel PDFs for years:
[...] Since the Pentium processor has two integer pipelines, a register used as the base or index component of an effective address calculation (in either pipe) causes an additional clock cycle if that register is the destination of either instruction from the immediately preceding clock cycle. This effect is known as Address Generation Interlock (AGI).
(ditto for the p6 core CPUs), and GCC (IIRC) tries to avoid AGI conflicts as much as possible. (and this kind of stuff belongs into the compiler)
Ingo
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