[PATCH][SelectionDAG] Increase coverage for checkForCycles

[Andrew Trick]

Hi Adam,

This looks great to me. For an internal diagnostic feature, I think it’s safe to commit and it’s easy for other developers to follow up post-commit if they want to.

-Andy

On May 30, 2014, at 12:06 PM, Adam Nemet <anemet at apple.com> wrote:

> Ping?
> 
> On May 21, 2014, at 11:02 AM, Adam Nemet <anemet at apple.com> wrote:
> 
>> This is a small patchset to provide better by-default diagnostics for DAG cycles.  Currently the check is only performed with ENABLE_EXPENSIVE_CHECKS=1.  After these changes we will also run it in Debug+Asserts.  To avoid slowing things down, we only perform the check when we would abort anyway due to some other inconsistency in the DAG detected in AssignTopologicalOrder.
>> 
>> So now, in addition to the cryptic "Overran sorted position”, we also get the node printed where the cycle starts.  Hopefully this will provide more actionable bug report.  This is motivated by my recent work on r209242.
>> 
>> OK to commit?
>> 
>> Adam
>> 
>> 
>> 
> <0001-SelectionDAG-Remove-duplicate-declaration.patch><0002-SelectionDAG-Pass-DAG-to-checkForCycles.patch><0003-SelectionDAG-Force-cycle-detection-in-AssignTopologi.patch>
>> 
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