8357381: C2: assert(false) failed: should not be here

[sarannat]

Issue
The assertion assert(false, "should not be here") in ConnectionGraph::move_inst_mem fires because a StoreB node has StrEquals as a memory user.

Analysis
The main issues starts after the first iteration of iterative escape analysis. As mentioned in JDK-8357381, EA#0 does lock removal. During IGVN after EA#0, the string intrinsic node StrEqual undergoes an ideal transformation (StrIntrinsicNode::Ideal()) which peels its MergeMem input node. At this point StoreB becomes a direct input of StrEquals.

Now EA#1 runs on the transformed graph. Phase 2 of split_unique_types explicitly allows StrEquals as a user of StoreB. In Phase 4, split_unique_types then calls move_inst_mem which is responsible for moving memory users to their memory slices. However, move_inst_mem only handles MergeMem, MemBar, Mem, and Phi as memory user. Since, StrEquals is not handled in move_inst_mem even though it is allowed in Phase 2 of split_unique_types it fires the assertion assert(false, "should not be here").

Solution
In the proposed fix, I have extended move_inst_mem to move string intrinsic nodes that are explicitly allowed in Phase 2 of split_unique_type to their appropriate memory slices.

Testing
Tier1-3 and Github actions

Question to reviewers
Please let me know if this fix looks reasonable.

Thank you @danielogh for the initial analysis.

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Issue

• JDK-8357381: C2: assert(false) failed: should not be here (Bug - P3)

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• 00: Full (0590a556)

[vnkozlov]

Can you add a new method to combine these check into one place and use it here and other places where which check these intrinsics?