[PATCH] Inverse post-order traversal for LiveVariables analysis, to recover the performance after r214064

[Ted kremenek]

Thanks Artyom.  I'll review this later today.

> On Aug 8, 2014, at 8:48 AM, Artyom Skrobov <Artyom.Skrobov at arm.com> wrote:
> 
> Thank you for the patience – indeed it took me some time to prepare the proper patch, which is now ready for review.
>  
> It comes without a regression test, as the only observable change is performance improvement of the analysis.
>  
>  
> From: Alexander Kornienko [mailto:alexfh at google.com] 
> Sent: 07 August 2014 23:35
> To: Artyom Skrobov
> Cc: cfe-commits at cs.uiuc.edu Commits
> Subject: Re: r214064 - Factoring DataflowWorklist out of LiveVariables and UninitializedValues analyses
>  
> Any news here? This keeps biting us.
>  
> Maybe you can apply this patch first and work on a better solution after that?
> 
> On Tue, Aug 5, 2014 at 6:23 PM, Artyom Skrobov <Artyom.Skrobov at arm.com> wrote:
> So, the simplest way to restore the original behaviour seems to be
>  
> Index: lib/Analysis/LiveVariables.cpp
> ===================================================================
> --- lib/Analysis/LiveVariables.cpp   (revision 214183)
> +++ lib/Analysis/LiveVariables.cpp   (working copy)
> @@ -451,6 +451,7 @@
>    // Construct the dataflow worklist.  Enqueue the exit block as the
>    // start of the analysis.
>    DataflowWorklist worklist(*cfg, AC);
> +  worklist.quick_hack();
>    llvm::BitVector everAnalyzedBlock(cfg->getNumBlockIDs());
>    // FIXME: we should enqueue using post order.
> Index: include/clang/Analysis/Analyses/DataflowWorklist.h
> ===================================================================
> --- include/clang/Analysis/Analyses/DataflowWorklist.h     (revision 214183)
> +++ include/clang/Analysis/Analyses/DataflowWorklist.h     (working copy)
> @@ -53,6 +53,7 @@
>    const CFGBlock *dequeue();
>    void sortWorklist();
> +  void quick_hack() { enqueuedBlocks.reset(); PO_I = PO_E; }
> };
>  } // end clang namespace
>  
> This has the effect of disabling the fallback post-order iteration.
>  
> The reason for the performance regression, however, is related to the iteration order over the CFG: UninitializedValues expects to use the default (i.e. reverse) PostOrderCFGView iteration, whereas LiveVariables expects the opposite order, corresponding to using llvm::GraphTraits<llvm::Inverse<const CFG*> > > as the last parameter in typedef po_iterator.
>  
> I’m currently thinking of a proper solution which would allow using PostOrderCFGView for iteration in either direction.
>  
>  
>  
> From: Alexander Kornienko [mailto:alexfh at google.com] 
> Sent: 05 August 2014 12:30
> 
> To: Artyom Skrobov
> Cc: cfe-commits at cs.uiuc.edu Commits
> Subject: Re: r214064 - Factoring DataflowWorklist out of LiveVariables and UninitializedValues analyses
>  
> On another file from the same project the difference in my setup is 2 minutes before the patch vs. 50+ hours (I terminated the analyzer before it finished) after the patch. So it's a rather bad performance regression.
>  
> 
> <DataflowWorklistInverse.patch>
> _______________________________________________
> cfe-commits mailing list
> cfe-commits at cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/cfe-commits
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/cfe-commits/attachments/20140808/4f597bda/attachment.html>