[15] RFR(XS): 8239852:java/util/concurrent tests fail with +VerifyGraphEdges: assert(!VerifyGraphEdges) failed: verification should have failed

[Christian Hagedorn]

Hi

Please review the following patch:
https://bugs.openjdk.java.net/browse/JDK-8239852
http://cr.openjdk.java.net/~chagedorn/8239852/webrev.00/

The failing assert is too strong in some cases where the IR is valid but 
PhaseCFG::schedule_late() bails out at [1] and the recompilation with 
subsume_loads == false does not bail out anymore.

One such case occurs during the compilation of 
java.util.concurrent.locks.AbstractQueuedLongSynchronizer::hasQueuedPredecessors 
when running, for example, [2] with -XX:+VerifyGraphEdges. Before 
calling PhaseCFG::insert_anti_dependences(), LCA and early both point to 
block A with _dom_depth x for some node. However, the early block is 
temporarily changed inside insert_anti_dependences() by 
memory_early_block() to point to an earlier block B with _dom_depth y < 
x. The LCA is updated to point to block B and is returned. As a result, 
the assert fails because early->_dom_depth (x) > LCA->_dom_depth (y). 
The recompilation of the method with subsume_loads == false does not 
bail out anymore.

The assert can be completely remove since we already have this assert 
[3] which catches an unschedulable graph of a compilation with 
subsume_loads == false and there are no other bailouts in 
PhaseCFG::schedule_late().


Thank you!

Best regards,
Christian


[1] 
http://hg.openjdk.java.net/jdk/jdk/file/61ee15b9a1ac/src/hotspot/share/opto/gcm.cpp#l1349
[2] 
http://hg.openjdk.java.net/jdk/jdk/file/61ee15b9a1ac/test/jdk/java/util/concurrent/Semaphore/RacingReleases.java
[3] 
http://hg.openjdk.java.net/jdk/jdk/file/61ee15b9a1ac/src/hotspot/share/opto/gcm.cpp#l1352