8355674: C2: Partial Peeling should not introduce Phi nodes above OpaqueInitializedAssertionPredicate nodes

[chhagedorn]

In the test case, we have two Initialized Assertion Predicate that share the same Bool which is perfectly fine:

These Initialized Assertion Predicates were created for loops that have been folded away. They then end up in a new inner most loop which is partial peeled. Partial Peeling finds that we need to do the cut between 580 IfTrue and 581 If. This means, that the Initialized Assertion Predicate 569 RangeCheck with its 535 OpaqueInitializedAssertionPredicate is in the peel set and the second Initialized Assertion Predicate 504 RangeCheck with its 503 OpaqueInitializedAssertionPredicate is in the not peel set. As a result of that, we are introducing a Phi node between an OpaqueInitializedAssertionPredicate and a Bool node:

We eventually remove the OpaqueInitializedAssertionPredicate and are left with the following graph shape

which cannot be handled by the backend.

The fix I propose is to prohibit Partial Peeling from inserting such a Phi node by updating clone_for_special_use_inside_loop() which takes care of not inserting phis for an If/Bool. We need to also special case OpaqueInitializedAssertionPredicate.

Thanks,
Christian

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Issue

• JDK-8355674: C2: Partial Peeling should not introduce Phi nodes above OpaqueInitializedAssertionPredicate nodes (Bug - P3)

Reviewers

• Emanuel Peter (@eme64 - Reviewer)

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8355674: C2: Partial Peeling should not introduce Phi nodes above OpaqueInitializedAssertionPredicate nodes

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• b21b3a3: 8355528: Update HarfBuzz to 11.2.0
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• 9477c42: 8356276: JavaScript error in script.js after JDK-8348282
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[eme64]

Thanks for fixing this, looks reasonable :)

[eme64]

What about a run without Xcomp?

[chhagedorn]

We would probably then also need to add some more invocations of test() inside main(). Probably does not hurt. The test is quite fast. I've updated the test.

[chhagedorn]

Thanks for your review Emanuel!