RFR: 8322694: C1: Handle Constant and IfOp in NullCheckEliminator [v3]

[Denghui Dong]

> This patch added the support for Constant and IfOn in NullCheckEliminator to eliminate more null check.
> 
> testing: tier 1-4 no extra test failure

Denghui Dong has updated the pull request incrementally with one additional commit since the last revision:

  should visit IfOp directly

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/17191/files
  - new: https://git.openjdk.org/jdk/pull/17191/files/68952fcc..34c704ab

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=17191&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=17191&range=01-02

  Stats: 2 lines in 1 file changed: 1 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/17191.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/17191/head:pull/17191

PR: https://git.openjdk.org/jdk/pull/17191