RFR: 8259777: Incorrect predication condition generated by ADLC

[Jatin Bhateja]

Please consider following instruction selection pattern:-

`   match(Set dst (VectorBlend (Binary src1 (AddVB src1 src2)) mask));
`

Currently, ADLC emits following predication check for src1 in matcher DFA.

`   /*src1*/(_kids[0]->_kids[0]->_leaf == _kids[1]->_kids[0]->_leaf) 
`

src1 appears twice in the State tree corresponding to this pattern, first as the leaf of left child state of Binary node which is
left child state of VectorBlend and secondly as the leaf of left child of AddVB which is the right child state of Binary node.
Thus following is the correct predication check to test both the occurrences of src1.

`   /*src1*/(_kids[0]->_kids[0]->_leaf == _kids[0]->_kids[1]->_kids[0]->_leaf)
`

This patch does a minor re-organizes the predication generation algorithm to fix this issue.

Validated that there is no change in generated DFA for current X86 AD files with and without this patch since such instruction patterns do not exist in AD files currently.

-------------

Commit messages:
 - 8259777: Incorrect predication condition generated by ADLC

Changes: https://git.openjdk.java.net/jdk/pull/2080/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=2080&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8259777
  Stats: 26 lines in 2 files changed: 15 ins; 0 del; 11 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2080.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2080/head:pull/2080

PR: https://git.openjdk.java.net/jdk/pull/2080