RFR: JDK-8272574: Crashes in PhaseIdealLoop::build_loop_late_post_work

王超 github.com+25214855+casparcwang at openjdk.java.net
Tue Aug 17 12:08:41 UTC 2021


Current loop predication will promote nodes(with a dependency on a later control node) to the insertion point which dominates the later control node.

In the following example, loopPrediction will promote node 434 to the outer loop(predicted insert point is right after node 424), and it depends on control node 207.  But node 424 dominates node 207, which means after the promotion, the cloned nodes have a control dependency on a later control node, which leads to a bad graph.

![image](https://user-images.githubusercontent.com/25214855/129720970-ff65b8f4-8bef-401d-8590-54aca6de470e.png)

![image](https://user-images.githubusercontent.com/25214855/129721369-4c61222b-7305-4522-9a37-e3e6e2138aa9.png)

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Commit messages:
 - Add test
 -  fix wrong loop predication

Changes: https://git.openjdk.java.net/jdk/pull/5142/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=5142&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8272574
  Stats: 37 lines in 3 files changed: 34 ins; 0 del; 3 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5142.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5142/head:pull/5142

PR: https://git.openjdk.java.net/jdk/pull/5142


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