RFR: 8254269: simplify Node::disconnect_inputs [v2]

[Xin Liu]

> 8254269: simplify Node::disconnect_inputs

Xin Liu has updated the pull request incrementally with one additional commit since the last revision:

  8254269: simplify Node::disconnect_inputs
  
  Optimize it for the precedence loop. because there's no null between
  2 non-null precedences, disconnect_inputs can break at a null value.

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/589/files
  - new: https://git.openjdk.java.net/jdk/pull/589/files/4a9d8030..b8a72755

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=589&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=589&range=00-01

  Stats: 17 lines in 1 file changed: 7 ins; 3 del; 7 mod
  Patch: https://git.openjdk.java.net/jdk/pull/589.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/589/head:pull/589

PR: https://git.openjdk.java.net/jdk/pull/589