[llvm-dev] Heap Exhaustion during 'DAGCombiner::Run'

[Martin J. O'Riordan via llvm-dev]

Thanks for this advice Nirav.  I have only just returned to working on this after being side-tracked to other tasks.

 

All the best,

 

            MartinO

 

From: Nirav Davé [mailto:niravd at google.com] 
Sent: 01 March 2018 20:45
To: MartinO at theheart.ie
Cc: llvm-dev <llvm-dev at lists.llvm.org>
Subject: Re: [llvm-dev] Heap Exhaustion during 'DAGCombiner::Run'

 

Martin:

 

I suspect this is an issue with post-DAG legalization store merging in the DAGCombiner. If you have a custom lowered type the DAGCombiner may end up merging a set of stores and immediately splitting them up in legalization. You should be able to disable this pass universally by overriding mergeStoresAfterLegalization() or conditionally for cases that shouldn't match with canMergeStoresTo. 

 

You should able able to verify by finding the loop of nodes considered with "-debug" on.

 

-Nirav

 

 

 

On Sun, Feb 25, 2018 at 9:36 AM Martin J. O'Riordan via llvm-dev <llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org> > wrote:

Hi LLVM-Devs,

I am in the process of updating our out-of-tree implementation from v5.0 to
v6.0 RC3, and while it builds and mostly runs, I am having trouble with a
small number of tests where the 'WorklistMap' in 'DAGCombiner::Run' never
becomes empty.  This is resulting in a runaway state of continuous heap
allocation until the process exhausts all system memory.

But I can't get a handle on why it is doing this, and it is not obvious to
me that the changes between v5.0 and v6.0 RC3 invalidate our implementation
in a way that might cause this.  The only time I see our code entered is
when lowering is called for vector element insert by 'LegalizeOp'.  Does
anybody have an advice on how I should approach debugging this?

Thanks,

        MartinO


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