[release/10.0] Fix LoaderHeap's free list growing more than expected

[eduardo-vp]

Backport of #129203 to release/10.0

Customer Impact

• Customer reported
• Found internally

This is a regression that impacts apps running test suites, running sometimes even 6x to 8x slower on Linux. Reported in #123124, in particular in this comment #123124 (comment).

Regression

• Yes
• No

Testing

Tested performance with the benchmark provided by the customer and another one in #129203 (comment). The issue happens under a high volume of method instantiations, we don't have such test. We could consider adding one.

Risk

Medium/Low. Actually the change is not that big - SatisfiesMethodConstraints is refactored and calls SatisfiesMethodConstraintsForInstantiation now. Also, inside InstantiatedMethodDesc::NewInstantiatedMethodDesc we previously took a lock, released it and took it again. Now we just don't release it in the middle and the call to SatisfiesMethodConstraints was moved to the beginning of the method. Unfortunately the github diff is way bigger than it should.

I also let the change sit in main for one week and no issues were linked to the original PR.

IMPORTANT: If this backport is for a servicing release, please verify that:

• For .NET 8 and .NET 9: The PR target branch is release/X.0-staging, not release/X.0.
• For .NET 10+: The PR target branch is release/X.0 (no -staging suffix).

Package authoring no longer needed in .NET 9

IMPORTANT: Starting with .NET 9, you no longer need to edit a NuGet package's csproj to enable building and bump the version.
Keep in mind that we still need package authoring in .NET 8 and older versions.

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[Copilot]

Pull request overview

This PR backports the .NET 10 fix for a severe performance regression caused by UnlockedLoaderHeap free-list growth during high-concurrency generic method instantiation. It prevents multiple threads from racing to allocate and then discard redundant InstantiatedMethodDesc allocations, which previously inflated the free list and made subsequent allocations increasingly expensive.

Changes:

• Added a shared helper (SatisfiesMethodConstraintsForInstantiation) to evaluate generic method constraints given an explicit instantiation.
• Changed InstantiatedMethodDesc::NewInstantiatedMethodDesc to hold m_InstMethodHashTableCrst across lookup and creation/insertion, ensuring only one thread allocates/registers a MethodDesc per instantiation.
• Refactored MethodDesc::SatisfiesMethodConstraints to delegate to the new helper.

[svick]

Hi,

the code complete date for 10.0.10 (the July 2026 release) is 24 June. Make sure to merge this PR on that date at the latest (or explicitly let me know that I should merge it), or it won't make it into that release.

As a reminder, if this is a product change, you also need Tactics approval before merging this PR (test-only or infra-only changes don't require Tactics approval).

[eduardo-vp]

/ba-g Ran the pipeline a second time, the only failure it's because of that (Artifact CoreCLRCrossDacArtifacts already exists).

[JulieLeeMSFT]

We have a tactics approval, but given the risk, we should run it for a few more weeks before merging.