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Re: Alias Analysis Improvement Patch

On Fri, 13 Jun 2003, Vladimir N. Makarov wrote:

> In average gcc with the patch is worse especially for twolf.  I think I
> should search for the reason of degradation in counteraction of scheduler
> and alias analysis.
> The compiler is also slower ~25% (890s vs 1140 s) with the new alias
> analysis on SPECINT2000.
> I did not check the code size (it is not important for Itanium).

Checking the code size for SPEC might be informative.

On the SH, when we naively enable the first scheduling pass, it greatly
lengthens the register lifetimes and forces the register allocator to
spill more often. This is easily noticeable as increased code size due to
extra stack load/stores emitted.

On the ia64, the improved alias analysis might allow the first instruction
scheduling pass more freedom to move instructions around and similarly
increase register lifetimes. This would probably show up as increased code
size as well.

(Although with 128 registers, you're less likely to run into this
 problem...but 128 is still a finite number of registers.)


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