Integrated: 8371881: C2: Fix potential SEGV in VTransformReductionVectorNode tracing

[Vishal Chand]

On Fri, 14 Nov 2025 13:24:14 GMT, Vishal Chand <duke at openjdk.org> wrote:

> This PR fixes a potential SEGV and removes dead code:
> • **Fix**: Prevent potential SEGV in VTransformReductionVectorNode - [from @shipilev] This fixes a crash in diagnostic code when isa_ReductionVector() unexpectedly returns nullptr. While this indicates the graph is already corrupted, the additional crash in `TRACE_OPTIMIZE` makes debugging harder. The fix adds defensive null checking to prevent the diagnostic crash and improve error handling.
> 
> • **Cleanup**: Remove unused first_red variable

This pull request has now been integrated.

Changeset: 16557739
Author:    Vishal Chand <vishalvc at amazon.com>
Committer: Aleksey Shipilev <shade at openjdk.org>
URL:       https://git.openjdk.org/jdk/commit/16557739791ada59dc1991f65a0218434df01f9e
Stats:     6 lines in 1 file changed: 4 ins; 1 del; 1 mod

8371881: C2: Fix potential SEGV in VTransformReductionVectorNode tracing

Reviewed-by: shade, epeter

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PR: https://git.openjdk.org/jdk/pull/28323