RFR: 8297264: C2: Cast node is not processed again in CCP and keeps a wrong too narrow type which is later replaced by top
Christian Hagedorn
chagedorn at openjdk.org
Thu Dec 1 09:47:07 UTC 2022

During CCP, we optimize the type of `348 CastII` in `CastIINode::Value()`: It matches the `CmpI/If` pattern because the current type of `119 Phi` is a constant int:
https://github.com/openjdk/jdk/blob/9f24a6f43c6a5e1fa92275e0a87af4f1f0603ba3/src/hotspot/share/opto/castnode.cpp#L213-L215
Later in CCP, the type of `119 Phi` is updated and is no longer a constant but `348 CastII` is not processed anymore during CCP and keeps its wrong too narrow type. We apply more loop opts and at some point, the `CastII` is replaced by top because the input type is outside of the wrong type range of the `CastII`. Some data nodes are folded and the graph is left in a broken state and we assert during GCM.
I propose to add a `CastII` node back to the CCP worklist if we find such a `Cmp/If` pattern to ensure that the `CastII` type is correctly set during CCP.
Thanks,
Christian
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Commit messages:
- 8297264: C2: Cast node is not processed again in CCP and keeps a wrong too narrow type which is later replaced by top
Changes: https://git.openjdk.org/jdk/pull/11448/files
Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=11448&range=00
Issue: https://bugs.openjdk.org/browse/JDK-8297264
Stats: 81 lines in 3 files changed: 81 ins; 0 del; 0 mod
Patch: https://git.openjdk.org/jdk/pull/11448.diff
Fetch: git fetch https://git.openjdk.org/jdk pull/11448/head:pull/11448
PR: https://git.openjdk.org/jdk/pull/11448
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