RFR: 8355230: Crash in fuzzer tests: assert(n != nullptr) failed: must not be null

[Emanuel Peter]

On Fri, 16 May 2025 14:16:29 GMT, Roland Westrelin <roland at openjdk.org> wrote:

> During IGVN, `TypeNode::make_paths_from_here_dead()` follows data
> nodes until a `Phi`. The `Region` input for the input that that logic
> goes through to reach the `Phi` is `null` causing the crash. I propose
> simply adding an extra check for that corner case.

How do we get to this case that the `phi->in(j) != nullptr` but `region->in(j) == nullptr`?

I agree with @TobiHartmann : it is generally nicer if the test is a little more cleaned up, and if possible even some comments on how we get to the pattern in question. It can make it easier for someone encountering issues with this test later. But we leave that up to you, and also understand if you don't want to spend too much time on it.

test/hotspot/jtreg/compiler/c2/TestNullRegionInputAtPhiMakePathDead.java line 28:

> 26:  * @bug 8355230
> 27:  * @summary Crash in fuzzer tests: assert(n != nullptr) failed: must not be null
> 28:  * @run main/othervm -XX:CompileCommand=compileonly,TestNullRegionInputAtPhiMakePathDead::* -Xcomp TestNullRegionInputAtPhiMakePathDead

What about a run without `Xcomp`?

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PR Review: https://git.openjdk.org/jdk/pull/25268#pullrequestreview-2853328997
PR Review Comment: https://git.openjdk.org/jdk/pull/25268#discussion_r2097406552