proposal for compilation unil wide alias analyis

[Mark Mitchell]

Jan Hubicka wrote:

>>Agreed on both points -- both that it can be effective, and that we need 
>>to demonstrate that it works with GCC.  I think we want to avoid 
>>committing to (say) making the tree->rtl expanders accept only SSA-form 
>>GIMPLE until we can demonstrate that it will be a compile-time win to do so.
>>    
>>
>
>Only experiment in this direction I made so far was to build CFG at -O0
>unconditionally and do tree cleanup_cfg before expanding (this was
>needed for the CFG transparent RTL expansion task).  The results were
>about 4% speedup on combine.c compilation times. The speedup ranged from
>noise to 8% on real world testcases I tested even tought the tree
>cleanup_cfg is surprisingly expensive (ie doing 7 RTL cleanups accounts
>together 1/4th of time of the single tree cleanup, any idea why?)
>  
>
If the results were that good, is there any reason not to check in this 
change?  Perhaps you could post it and get people to evaluate it on some 
other code.  If we're seeing those kinds of improvements, we definitely 
want it!

-- 
Mark Mitchell
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mark@codesourcery.com