Debugging

• Debugging a Mismatch

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Debugging a Mismatch

So you've found that validation-test.py or plaidbench-validation-test.py reports a mismatch between two of your runs. How do we approach debugging this mismatch?

The first thing to verify is whether we should expect the runs to be mismatch-free. Mismatch checking only works if the costs between the runs are comparable. It's expected to have mismatches if you change the cost function, e.g. from PERP to SLIL.

Minimize the test case

If you discovered the mismatch from compiling all of SPEC CPU2006, choose a single benchmark which has a mismatch and only run that. Ideally, you'd choose a smaller benchmark rather than a larger one.

To determine which benchmark a block comes from, spills.dat from the output of runspec-wrapper-optsched.py shows the function names, making it possible to search that file for the given block (minus the :##; block names are functionName:#blkNumber#, e.g. foo:23).

Visualize the DDG

It can be very helpful to visualize the DDG for a small mismatch case, presuming there is a small mismatch case.

Dumping a DDG

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Visualizing the DDG

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