RFR: 8268882: C2: assert(n->outcnt() != 0 || C->top() == n || n->is_Proj()) failed: No dead instructions after post-alloc

[Rickard Bäckman]

Also delete Phi nodes with no uses.

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Commit messages:
 - 8268882: C2: assert(n->outcnt() != 0 || C->top() == n || n->is_Proj()) failed: No dead instructions after post-alloc

Changes: https://git.openjdk.java.net/jdk/pull/6270/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=6270&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8268882
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6270.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6270/head:pull/6270

PR: https://git.openjdk.java.net/jdk/pull/6270