RFR: 8267875: Shenandoah: Duplicated code in ShenandoahBarrierSetC2::ideal_node()

[Zhengyu Gu]

Node::set_req_X definition as:
void Node::set_req_X(uint i, Node *n, PhaseGVN *gvn) {
  PhaseIterGVN* igvn = gvn->is_IterGVN();
  if (igvn == NULL) {
    set_req(i, n);
    return;
  }
  set_req_X(i, n, igvn);
}

ShenandoahBarrierSetC2::ideal_node() duplicates above logic.


Test:
  hotspot_gc_shenandoah

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

Commit messages:
 - Merge branch 'master' into sh-c2-ideal-simplify
 - v1

Changes: https://git.openjdk.java.net/jdk/pull/4229/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=4229&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8267875
  Stats: 11 lines in 1 file changed: 0 ins; 9 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4229.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4229/head:pull/4229

PR: https://git.openjdk.java.net/jdk/pull/4229