RFR: 8312596: Potential null pointer access in Compile::TracePhase::~TracePhase after JDK-8311976

[Dean Long]

On Mon, 24 Jul 2023 18:16:19 GMT, Ashutosh Mehra <duke at openjdk.org> wrote:

> Please review this PR to fix a potential null pointer access in using `_compile`.
> Updated the code to unconditionally initialize `_compile` and added an assert (similar to C1's `PhaseTraceTime` constructor) for it to be non-null.

Marked as reviewed by dlong (Reviewer).

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PR Review: https://git.openjdk.org/jdk/pull/15002#pullrequestreview-1546174578