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Re: [RFC] Contributing tree-ssa to mainline

In message <>, Jan Hubicka write
 >There are other easy targets - NULL pointer ellimination for instance
 >that I was discussing with Jeff.
We could probably already turn off the RTL NULL pointer check elimination
code.  While I am aware of one case where the tree version misses something
the RTL version catches, that case is extremely rare.  Last I looked, it
triggered once per stage in a GCC bootstrap.

In contrast I've heard and seen firsthand the tree-ssa NULL pointer check
elimination code eliminating NULL pointer checks that the RTL version misses.

Jump threading/bypassing.  Right now we've got about 175 cases where the
RTL jump threader catches something that we should have detected at the
tree-ssa level (contrast this to > 3000 a few months ago).  I've got
patches in my local tree which bring that number down to around 40.

And (of course) I'm also seeing the tree-ssa code detect and thread a
number of jumps that the RTL threader is missing.

I haven't yet evaluated where we stand on making the RTL jump bypassing
code useless -- I know we're detecting some of that stuff in the tree-ssa
jump threader, but I really haven't evaluated it yet.

We're also reasonably close to being able to simplify CSE in a major
way -- specifically we're close to having the ability to turn off
the path following code in CSE1.


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