JIT: Only look for integer temp regs in prolog generation

[jakobbotsch]

Otherwise we may end up with mask registers in this mask, and passing that to genFindLowestBit hits asserts. We are in any case only interested in integer registers here, so limit it to that.

Fix #118925

[dotnet-policy-service]

Tagging subscribers to this area: @JulieLeeMSFT, @jakobbotsch
See info in area-owners.md if you want to be subscribed.

[Copilot]

Pull Request Overview

This PR fixes a JIT (Just-In-Time compiler) issue where mask registers could incorrectly be included when searching for temporary registers during prolog generation, causing assertion failures in genFindLowestBit. The fix restricts the search to only integer registers by applying the RBM_ALLINT mask.

• Adds filtering to ensure only integer registers are considered for temporary register allocation
• Prevents mask registers from being passed to genFindLowestBit which expects integer registers only

[jakobbotsch]

PTAL @dotnet/jit-contrib. No diffs. Just fixes an assert when we have TYP_MASK locals whose registers end up in the set here.

No need to backport this, the assert that triggers is harmless.

[tannergooding]

Are there any other places where we might not be filtering out float or mask registers that we should?

I know I've found a few places over time (and fixed them as encountered) where we basically did things like assume !isFloatReg meant must be an integer register and similar.

[jakobbotsch]

Are there any other places where we might not be filtering out float or mask registers that we should?

I audited a few files but couldn't find other cases... I guess we will see when we hit them.