Re: [tree-ssa] alias analysis

[Daniel Berlin <dberlin at dberlin dot org>]

> Yes, splitting the sets would work too, but that seems to be avoiding
> the real issue -- creating too many useless alias relationships to 
> begin
> with.
It's funny you mention creating too many useless alias relationships vs 
splitting sets.
Splitting sets doesn't help make it faster.
Turning on PTA makes it split sets a lot more right now (since we can 
disambiguate so much better).
On 20001226-1.c, it takes a little over a second and a half (I can 
actually make it take well under a second, but it's not a priority for 
me since i think 1.68 seconds is an okay number here) to compute the 
points-to results
tree PTA              :   1.68 ( 1%) usr   0.11 ( 8%) sys   1.87 ( 1%) 
wall

However, because of the extra set splitting that happens, phi insertion 
time goes through the roof:
 tree PHI insertion    :  50.27 (18%) usr   0.05 ( 3%) sys  52.36 (18%) 
wall

This is with *always* using alias sets, and just using PTA to 
disambiguate.

(In case someone tries this, tree alias analysis time goes through the 
roof, but this is just a red herring. I've already fixed it in my tree)

So be careful with extra set splitting, it'll currently drive your phi 
insertion time up (whether it should or not is another matter)

On a random note, do either of you plan on making calls to may_alias_p 
from outside of tree-dfa.c anymore?

I had moved the freeing of PTA memory to SSA deletion time when Diego 
was doing alias tags, and using may_alias_p in tree-ssa.c, but if it's 
not going to be called during SSA building anymore, i'll move the 
freeing of PTA memory back to where it used to be.
> Jeff