[15] RFR(S): 8235332: TestInstanceCloneAsLoadsStores.java fails with -XX:+StressGCM

[Christian Hagedorn]

Hi Roland

>> http://cr.openjdk.java.net/~chagedorn/8235332/webrev.00/
> 
> If there's no GC barrier then:
> 
> Node* control_proj_ac = bs->step_over_gc_barrier(proj_in->in(0));
> 
> control_proj_ac is not a projection, it's proj_in->in(0) so the test
> below can never succeed?

If there is no GC barrier, then proj_in is a membar with its control 
input being a control projection from the ArrayCopyNode.

As an example, I have taken the test case TestEliminatedCloneBadMemEdge 
[1] which does not disable ReduceInitialCardMarks and has no GC barrier. 
We have the following situation at [2]:

proj_in is 132 MemBarCPUOrder. The original code then looked at the 
MergeMem 100 input following in(Compile::AliasIdxRaw) which is 101 Proj 
and its input 98 ArrayCopy. This passes the check.

My fix now directly looks at the control input of 132 MemBarCPUOrder 
which is the projection 99 Proj coming from the 98 ArrayCopy. This also 
passes the check.


  98	ArrayCopy	===  85  1  65  8  1 ( 47 _  90 _  97 _ _ _ _ ) [[ 99 
101 ]]  void ( java/lang/Object *, int, java/lang/Object *, int, int, 
int, int, BotPTR *+bot, BotPTR *+bot ) (clone, tightly coupled 
allocation) !jvms: TestEliminatedCloneBadMemEdge::test @ bci:1
  101	Proj	===  98  [[ 100 ]] #2  Memory: @rawptr:BotPTR, idx=Raw; 
!jvms: TestEliminatedCloneBadMemEdge::test @ bci:1
  100	MergeMem	=== _  1  39  101  86  1  86  86  86  86  86  86  86  86 
86  86  [[ 132 ]]  { N101:rawptr:BotPTR N86:java/lang/Object+8 ...
  99	Proj	===  98  [[ 132 ]] #0 !jvms: 
TestEliminatedCloneBadMemEdge::test @ bci:1
  132	MemBarCPUOrder	===  99  1  100  1  1  [[ 104  103 ]]  !orig=102 
!jvms: TestEliminatedCloneBadMemEdge::test @ bci:1


Best regards,
Christian


[1] 
http://hg.openjdk.java.net/jdk/jdk/file/2080e45e61ea/test/hotspot/jtreg/compiler/arraycopy/TestEliminatedCloneBadMemEdge.java
[2] 
http://hg.openjdk.java.net/jdk/jdk/file/f7edb9ca045c/src/hotspot/share/opto/escape.cpp#l2749