RFR(S): 8161652 Crash with assert(ft == _type) failed in PhiNode::Value()

[Roland Westrelin]

The crash occurs when processing a phi with all inputs to null and the
type of the phi is not null. The phi is in a dying part of the graph and
is processed before the control flow is killed. The inputs are set to
null by logic in PhiNode::Ideal() because it finds an unique input when
looking through cast nodes. The phi before its inputs are changed is:

 26	ConP	===  0  [[ 27  35  76  83  128  127  154  3323  3300  3301  3259  3236  3237  3195  3172  3173  3131  3108  3109  2852  513  3067  3044  642  724  906  1054  1159  1166  1241  1240  3045  1261  3032  1314  1326  1325  2990  1391  1398  1440  1573 
1580  1604  1636  1678  1677  1700  1762  1771  3024  1804  1930  2059  2938  2141  2915  647  2916  2444  2902  2593  2895  2690  2776  2845  513 ]]  #NULL
 647	CastPP	===  3398  26  [[ 659  708  648  648  656  659 ]]  #java/util/Map:NotNull *  Interface:java/util/Map:NotNull * !jvms: HashMap::putMapEntries @ bci:1 HashMap::<init> @ bci:13 NamespaceSupport$Context::copyTables @ bci:52
NamespaceSupport$Context::<init> @ bci:30 NamespaceSupport::pushContext @ bci:85
 656	CheckCastPP	===  3402  647  [[ 683  708  683 ]]  #java/util/LinkedHashMap:NotNull:exact *  Oop:java/util/LinkedHashMap:NotNull:exact * !orig=[682] !jvms: HashMap::putMapEntries @ bci:1 HashMap::<init> @ bci:13 NamespaceSupport$Context::copyTables @
bci:52 NamespaceSupport$Context::<init> @ bci:30 NamespaceSupport::pushContext @ bci:85
 695	Region	===  695  3402  667  [[ 695  715  696  697  698  699  700  701  702  703  704  705  706  707  708  709 ]]  !jvms: HashMap::putMapEntries @ bci:-1 HashMap::<init> @ bci:13 NamespaceSupport$Context::copyTables @ bci:52 NamespaceSupport$Context::<init>
@ bci:30 NamespaceSupport::pushContext @ bci:85
 708	Phi	===  695  656  647  [[ 877  870  870  840  880  809 ]]  #java/util/Map:NotNull *  Interface:java/util/Map:NotNull * !jvms: HashMap::putMapEntries @ bci:-1 HashMap::<init> @ bci:13 NamespaceSupport$Context::copyTables @ bci:52
NamespaceSupport$Context::<init> @ bci:30 NamespaceSupport::pushContext @ bci:85

A unique input is found, the logic creates a CheckCastPP with a null
input which is transformed to null. The logic should create a CastPP in
that case. Because the compiler expects cast to non null to happen
through a CastPP and cast to a new class to happen through a
CheckCastPP, I suggest the logic be changed so it can create one CastPP
and a CheckCastPP when needed:

http://cr.openjdk.java.net/~roland/8161652/webrev.00/

Roland.