[WIP] Fix JIT issue with equality-guarded derived long comparison

[Copilot]

• Read issue details and applicable repo/build/JIT/test instructions
• Check recent GitHub Actions runs/logs for the required CI workflow; observed unrelated service-label failure on another PR
• Establish required CoreCLR/runtime-test baseline before product changes
• Add focused JIT regression test for JIT: equality-guarded derived long comparison can silently use a truncated 32-bit value on x64 #133251
• Confirm the product-code fix is already present in this checkout and keep the repository change test-only
• Run targeted build/test validation and formatting
• Scan changed files for secrets
• Run final automated validation

• FixesJIT: equality-guarded derived long comparison can silently use a truncated 32-bit value on x64 #133251

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[AndyAyersMS]

@copilot where is the fix?

[Copilot]

@copilot where is the fix?

There isn’t a product-code fix in this PR. The failure is already fixed in the current base by the prior JIT change in #132849 (RangeCheck::ComputeDoesOverflow now checks operand def chains for overflow). This PR only adds the missing regression coverage for #133251, and I verified that the new test runs and passes on a fresh checked CoreCLR/Core_Root build.

[AndyAyersMS]

Ah, ok. Good to know. I don't think we need another test.