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Re: fix for pr47837
On Tue, Mar 8, 2011 at 11:04 PM, Jeff Law <law@redhat.com> wrote:
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> On 03/08/11 11:55, Diego Novillo wrote:
>> On 03/08/2011 12:54 PM, Xinliang David Li wrote:
>>> Please review the attached patch, it does some simplification of the
>>> complicated logical or expressions (x1 or x2 or x3 ...) constructed
>>> from control flow analysis into simpler form.
>>>
>>> Bootstraps and works on s390x for both testcases.
>>>
>>> Bootstraps on x86-64. Regression testing is on going (it takes forever
>>> (whole night already) to finish possibly because the lto test in
>>> c-torture ..).
>>>
>>> Ok for trunk?
>>
>> As a general comment, do you think we will start adding more and more of
>> these special pattern matchers into uninit analysis? ?I'm wondering how
>> much effort should we make into creating something more generic.
>>
>> Right now it's this pattern, but there may be others. ?It could grow
>> pretty big and ugly.
> We have a real problem in that our underlying analysis to eliminate
> unexecutable edges is the CFG needs help, particularly for path
> sensitive cases.
>
> Given that I'm seeing a real interest in other analysis that ultimately
> have problems similar to those for uninitialized variable analysis,
> building too much goo into tree-ssa-uninit doesn't seem like a long term
> solution.
True. I've been repeatedly thinking of building some on-the-side CFG
with value-numbered predicates to also catch the CFG vs. scalar-code
predicate combinations we have. On such on-the-side data structure
we could do very aggressive jump-threading just for analysis purposes
(experiments when working on separating conditions shows that
a PRE-like algorithm could drive this).
Thanks,
Richard.