RFR: 8297264: C2: Cast node is not processed again in CCP and keeps a wrong too narrow type which is later replaced by top

[Tobias Hartmann]

On Thu, 1 Dec 2022 09:37:57 GMT, Christian Hagedorn <chagedorn at openjdk.org> wrote:

> ![image](https://user-images.githubusercontent.com/17833009/205015579-1b6ac082-e992-4828-80f7-ff991964179b.png)
> 
> 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

Looks good to me. FTR, the verification code I proposed in [JDK-8257197](https://bugs.openjdk.org/browse/JDK-8257197) would catch this.

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Marked as reviewed by thartmann (Reviewer).

PR: https://git.openjdk.org/jdk/pull/11448