RFR: 8304049: C2 can not merge trivial Ifs due to CastII

[Yi Yang]

Hi can I have a review for this patch? C2 can not apply Split If for the attached trivial case. PhiNode::Ideal removes itself by unique_input but introduces a new CastII, therefore we have two Cmp, which is not identical for split_if.


  public static void test5(int a, int b){
 
    if( b!=0) {
      int_field = 35;
    } else {
      int_field =222;
    }

    if( b!=0) {
      int_field = 35;
    } else {
      int_field =222;
    }
  }



Test: tier1, application/ctw/modules

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Commit messages:
 - 8304049: C2 can not merge trivial Ifs due to CastII

Changes: https://git.openjdk.org/jdk/pull/13039/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=13039&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8304049
  Stats: 53 lines in 7 files changed: 50 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/13039.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/13039/head:pull/13039

PR: https://git.openjdk.org/jdk/pull/13039