[PATCH] [Patch] Loop Interchange Pass

[hfinkel at anl.gov]

In http://reviews.llvm.org/D7499#123108, @karthikthecool wrote:

> Hi Hal,
>  Updated the test case to add a test case to cover case were we have a usage of PHI outside the loop. I have added gi,gj as global vaiable and used them as induction variables in the loop to simulate this case.
>
> It would be great if you could give me some inputs on writing test case for this pass. 
>  Currently the test cases i have added are all more or less similar(i.e. they get vectorized after interchange).
>  For checking loop that are just interchanged but not vectorized do we have to check the exact instructions after interchange or may be check the PHI instruction order in .ll (after interchange the Induction PHI will be in the reverse order) ?


Good point; I'd not looked carefully at the tests yet. We should not test this pass by using the vectorizer, but rather, should test the output of the interchange pass directly.

We don't need to make this harder than necessary, but, I think that for a few representative cases, we should check all of the relevant parts of the output. Then for cases that are structurally similar to those, checking the PHI order (or some other signature of the interchange) is fine.

We also should have negative tests (some loops that aren't quite tightly nested, maybe with some function call or extra memory access, etc.) and make sure they're not interchanged. We should also add tests for current limitations (like that loops with reductions are not interchanged), and put in some FIXME comments stating that these are just current limitations.

Feel free to borrow IR from the files in test/Analysis/DependenceAnalysis and adapt them as tests here.

> Thanks

>  Karthik Bhat



http://reviews.llvm.org/D7499

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