[8u20, 9] RFR(S): 8011646 : SEGV in compiled code with loop predication

[Albert]

Hi,

could I get reviews for this small patch?

Bug:
https://bugs.openjdk.java.net/browse/JDK-8011646

Problem:
LibraryCallKit::inline_native_hashcode() uses a control input to the 
load node 'n' that loads the header.
'n' is connected to a castPP node, which maintains the dependency 
between the null check of 'n' and 'n'.
A later compiler phase removes this castPP. The dependency between the 
null check and 'n' is lost if
the 'n' has a control input (see MemNode::Ideal_common_DU_postCCP() ). 
The reason for the
lost dependency is that loop predication erroneously sets the control 
edge of the load to a predicate
that is hoisted out of the loop.
If, however, the load has no control edge, 
MemNode::Ideal_common_DU_postCCP() sets the control edge
correctly. This

The bug description contains a Java program that reproduces this 
behavior. Also, the bug description contains
a graph that can be viewed with the IGV. For example, the LoadL node 
(830) in Phase "After Parsing" has a
control edge that is connected to node 780. At the phase, the graph is 
still correct. In phase "InterGVN 2"
the control edge is connected to a node outside the loop. As a result, 
the dependency between the null
check and the load is lost.

Solution:
Do not add a control input to the load. As a result, the control to the 
load is set correctly when the castPP node
is removed.

Webrev:
http://cr.openjdk.java.net/~anoll/8011646/webrev.00/

Testing:
Failing test case, regression test, jprt



Many thanks to Roland and Vladimir who helped me a lot with this bug.

Best,
Albert
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