[llvm] r261430 - When MemoryDependenceAnalysis hits a CFG with many transparent blocks,

[Tom Stellard via llvm-commits]

On Tue, May 03, 2016 at 08:38:28PM -0700, Philip Reames via llvm-commits wrote:
> 
> 
> On 05/01/2016 11:44 AM, Joerg Sonnenberger via llvm-commits wrote:
> >On Mon, Feb 22, 2016 at 11:03:09AM -0800, Hans Wennborg wrote:
> >>>>>New Revision: 261430
> >>>>>
> >>>>>URL: http://llvm.org/viewvc/llvm-project?rev=261430&view=rev
> >>>>>Log:
> >>>>>When MemoryDependenceAnalysis hits a CFG with many transparent blocks,
> >>>>>the algorithm easily degrades into quadratic memory and time complexity.
> >>>>>The easiest example is a long chain of BBs that don't otherwise use a
> >>>>>location. The caching will add an entry for every intermediate block and
> >>>>>limiting the number of results doesn't help as no results are produced
> >>>>>until a definition is found.
> >>>>>
> >>>>>Introduce a limit similar to the existing instructions-per-block limit.
> >>>>>This limit counts the total number of blocks checked. If the limit is
> >>>>>reached, entries are considered unknown. The initial value is 1000,
> >>>>>which avoids regressions for normal sized functions while still
> >>>>>limiting edge cases to reasnable memory consumption and execution time.
> >>>>>
> >>>>>Differential Revision: http://reviews.llvm.org/D16123
> >>>>Hello Hans,
> >>>>as mentioned on IRC the other day, I would like to see this merged into
> >>>>the 3.8 branch after the 3.8.0 release is cut. It fixes some long
> >>>>standing issues, but not regressions from earlier releases.
> >>>I do not believe this should be merged into 3.8.
> >>FWIW, I'm not considering this for 3.8.0 either, but what we said on
> >>IRC was that it might be a candidate for 3.8.1 if Tom finds it
> >>appropriate. In any case, it should get properly reviewed first.
> >Hi Tom,
> >this has been in the tree for while now without any issues. I've been
> >running with the merge for a while and it has helped to avoid the
> >problems it was supposed to address. Can it be merged, please?
> SGTM as well.
> 
> Philip


Hi Hal,

I think this pass falls in the Alias Analysis category.  Is it OK
to merge to the 3.8 branch: http://reviews.llvm.org/rL261430

Philip has already given the OK for this.

-Tom


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