[9] RFR(S): 8136818: Test compiler/arraycopy/TestEliminatedArrayCopyDeopt.java fails with "m1 failed"

[Tobias Hartmann]

Hi,

please review the following patch:
https://bugs.openjdk.java.net/browse/JDK-8136818
http://cr.openjdk.java.net/~thartmann/8136818/webrev.00/

The test fails because a non-escaping allocation is removed but re-allocation after deoptimization does not initialize the object with the correct values. The problem is that with -XX:-ReduceInitialCardMarks and -XX:+UseParallelGC we emit a StoreB in the post barrier between the ArrayCopy and the MemBarStoreStore (see GraphKit::write_barrier_post() and graph [1]). PhaseMacroExpand::value_from_mem() -> scan_mem_chain() -> ArrayCopyNode::may_modify() only expects a StoreCM node and therefore does not recognize the initializing ArrayCopy. As a result, the Object is re-allocated with uninitialized values.

I fixed this by adding the Op_StoreB case and moving the checks into ArrayCopyNode::may_modify_helper() to also recognize the card mark stores behind a Phi.

Tested with failing test, JPRT and RBT (running).

Thanks,
Tobias

[1] https://bugs.openjdk.java.net/secure/attachment/61959/graph.png