Restore stress guards on process-isolated IL tests

[EgorBo]

Fixes #131447.

Root cause

Not a JIT bug. #126108 replaced the <JitOptimizationSensitive> and <GCStressIncompatible> MSBuild properties with [SkipOnCoreClr(...)] attributes on test entry points. That works for C# tests and for in-process IL tests, but silently drops the guard for IL tests that also set <RequiresProcessIsolation>:

Test kind	What evaluates the skip	Result
C#, any isolation	GenerateStandaloneSimpleTestRunner compiles the check into __GeneratedMainWrapper.Main	✅ honored
IL, in-process	merged runner reads the attribute from metadata via ExternallyReferencedTestMethodsVisitor	✅ honored
IL + process isolation	merged runner emits an OutOfProcessTest that only calls RunOutOfProcessTest(...) on the generated run script, and ReferenceXUnitWrapperGenerator is gated on '$(Language)' == 'C#' so the IL assembly's hand-written .entrypoint never gets a wrapper either	❌ nothing reads the attribute

In that last case only the MSBuild property puts the guard into the generated .cmd/.sh.

arrres_il_r keeps its whole body in a single Main, so unoptimized codegen (tier-0, minopts, JIT stress) keeps the Test objects alive in untracked stack slots for the duration of Main. They are then never finalized and never resurrected, and the test throws. It fails on every default (tiered) run, which is why it lit up across outerloop, jitstress and pgo on all platforms at once.

Fix

Restore the MSBuild property on the two affected tests (option 1 from #126108 (comment)):

• arrres_il_r.ilproj → <JitOptimizationSensitive>
• b143840.ilproj → <GCStressIncompatible> (same bug, unguarded on gcstress legs; it kept <RequiresProcessIsolation> for <UnloadabilityIncompatible>)

The [SkipOnCoreClr] attributes are intentionally left in place, so the guard keeps working if either test ever stops requiring process isolation. Each project gets a comment explaining why the property cannot be dropped in favour of the attribute.

Fallout audit

I enumerated all 16 IL tests carrying [SkipOnCoreClr] and evaluated each owning project's effective RequiresProcessIsolation with msbuild -getProperty (so inherited Directory.Build.props/.targets values are accounted for). These two are the only process-isolated ones — the other 14 are in-process and unaffected.

I also confirmed empirically, rather than by inspection alone, that both of the "honored" rows above really do emit the guard, by disassembling the built assemblies:

• Directed_3.dll (merged runner, in-process IL) contains IsJitStress / IsJitStressRegs / IsJitMinOpts / IsTailCallStress / IsTieredCompilation checks guarding the call to [AttributeConflict]P::Main().
• ObjectStackAllocationTests.dll (process-isolated C#) contains the same checks inside __GeneratedMainWrapper.

No C# test is affected by this class of bug.

Validation

Built and ran the generated run scripts on windows-x64 checked:

arrres_il_r  default (tiered)     SKIP
             TieredCompilation=0  PASS  (Test passed., 100)
             TC=0 + JITMinOpts=1  SKIP
             TC=0 + JitStress=2   SKIP
b143840      default              PASS
             GCStress=0xC         SKIP

Before the change, arrres_il_r reproduced the exact CI signature under the default environment: unhandled System.Exception in GCTest_arrres_il.Test.Main, exit -532462766.

cc @jkoritzinsky @jakobbotsch @JulieLeeMSFT

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[Copilot]

Pull request overview

Restores MSBuild-based stress guards for process-isolated IL tests by reintroducing the appropriate project properties (since [SkipOnCoreClr] on hand-written IL .entrypoint methods is not evaluated in the out-of-process runner path).

Changes:

• Re-add <GCStressIncompatible>true</GCStressIncompatible> to b143840.ilproj, with rationale explaining why the MSBuild property is required for process-isolated IL tests.
• Re-add <JitOptimizationSensitive>true</JitOptimizationSensitive> to arrres_il_r.ilproj, with rationale covering both the optimization sensitivity and the process-isolation runner behavior.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
src/tests/JIT/Regression/CLR-x86-JIT/V1.1-M1-Beta1/b143840/b143840.ilproj	Restores GCStressIncompatible MSBuild guard for a process-isolated IL test and documents why the attribute alone isn’t sufficient.
src/tests/JIT/Methodical/Arrays/misc/arrres_il_r.ilproj	Restores JitOptimizationSensitive MSBuild guard for a process-isolated IL test and documents why it must remain.

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