RFR: 8331885: C2: meet between unloaded and speculative types is not symmetric

[Tobias Hartmann]

On Wed, 15 May 2024 13:30:46 GMT, Vladimir Ivanov <vlivanov at openjdk.org> wrote:

> `TypeInstPtr::xmeet_unloaded` computes the MEET of two InstPtrs when at least one is unloaded, but doesn't preserve speculative part if one is present. It causes the corresponding assert to fail. 
> 
> Proposed fix unconditionally keeps speculative part. 
> 
> Testing: hs-tier1 - hs-tier4

Looks good to me too. Please also run `hs-comp-stress` and `hs-precheckin-comp` testing.

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Marked as reviewed by thartmann (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/19249#pullrequestreview-2061044711