Integrated: 8347273: C2: VerifyIterativeGVN for Ideal and Identity

[Emanuel Peter]

On Wed, 8 Jan 2025 14:43:40 GMT, Emanuel Peter <epeter at openjdk.org> wrote:

> **Past Work**
> With https://github.com/openjdk/jdk/pull/11775 / [JDK-8298952](https://bugs.openjdk.org/browse/JDK-8298952) we added `Node::Value` verification.
> 
> **This PR**
> I'm now adding verification for `Ideal` and `Identity`. I'm adding two bits to the flag `VerifyIterativeGVN`.
> 
> I found many many  node types that hit my verification assert, i.e. that could still be optimized after IGVN is over, just because these nodes were not put on the worklist any more.
> 
> My approach was to aggressively bail-out for all nodes that had an issue. This way, we can address one by one in follow-up RFEs. For many, I did some initial assessment, and left some comments about what issues I encountered.
> 
> **Future Work:**
> In many cases, the issue is just a missing notification when inputs of inputs are changed. These would be good starter tasks. But there are probably also more complicated cases. And there are surely cases where verification will be impossible, because it is possible that the Idea / Identity optimizations traverse longer paths, and we cannot expect that notification makes it down that path. For those cases, we will have to leave the exception and document it well.
> 
> I filed:
> [JDK-8359103](https://bugs.openjdk.org/browse/JDK-8359103) C2 VerifyIterativeGVN: Umbrella for extending Ideal and Identity verification (JDK-8347273)
> (We can file subtasks for the nodes we want to fix. I don't want to file them all now, but we should file them as we are investigating, so that there is no duplicate work.)
> 
> Testing passed tier1-3, with extra timeout factor 20.

This pull request has now been integrated.

Changeset: dd688290
Author:    Emanuel Peter <epeter at openjdk.org>
URL:       https://git.openjdk.org/jdk/commit/dd68829017c3adea4068d5311cab3fbef87b9577
Stats:     925 lines in 5 files changed: 900 ins; 0 del; 25 mod

8347273: C2: VerifyIterativeGVN for Ideal and Identity

Reviewed-by: chagedorn, mhaessig

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PR: https://git.openjdk.org/jdk/pull/22970