[RFC] Variable Expansion in unroller

[Revital Eres <ERES at il dot ibm dot com>]

Hello,

Attached is the patch for variable expansion in unroller.
Considering the last discussions on the register pressure utility
and the current status of gcc;
I resubmit this patch without the register pressure utility
but with a restriction to only one expansion per 
accumulator to avoid register pressure.
This parameter can be redefined by setting
--param max-variable-expansions-in-unroller=value.

The testing I made on POWER4 without the restriction on the number
of expansions showed 1.2% improvement on SPECFP
with 5% improvement to art benchmark.
When running SPECFP (only c benchmark this time) with the 
restriction on the expansions (the default restriction) I got 4.8% 
improvement on art benchmark.
I hope to post some more results later this week.

I'll submit this patch once all the regression tests are done.

Comments are welcome,
Revital

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