JIT: Make LACKS_RETURN callsite-specific

[AndyAyersMS]

Summary

The inliner records LACKS_RETURN when contextual import finds no suitable
return expression. Since this can depend on call-site specialization, classify
the observation as CALLSITE so one failed attempt does not permanently mark
the callee as uninlineable.

Callees with no return blocks are already handled by
CALLEE_DOES_NOT_RETURN.

Testing

• build.cmd clr+libs -c Checked
• build.cmd clr.jit -c Checked

Note

This pull request description was generated with GitHub Copilot.

[azure-pipelines]

Azure Pipelines:
Successfully started running 5 pipeline(s).
11 pipeline(s) were filtered out due to trigger conditions.
There may be pipelines that require an authorized user to comment /azp run to run.

[dotnet-policy-service]

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

[AndyAyersMS]

A small tweak to a rarely-made observation.

CALLEE noinline observations are usually propagated back to the runtime to inhibit future inline attempts, CALLSITE observations just fail the current attempt. This observation is contextual (can depend on call site), so classify it that way.

@EgorBo PTAL
fyi @dotnet/jit-contrib

[Copilot]

🟢 Approval recommended

The change is localized, references were updated consistently (no remaining CALLEE_LACKS_RETURN usages), and the new target aligns with how LegalPolicy treats CALLSITE vs CALLEE fatal observations.

Pull request overview

Updates the JIT inlining observation for “missing return expression” to be callsite-scoped rather than callee-scoped, so a failure to materialize a return value during a particular inline attempt doesn’t permanently mark the callee as never-inline.

Changes:

• Reclassify LACKS_RETURN from CALLEE to CALLSITE and adjust its diagnostic text.
• Update the inliner failure path to report CALLSITE_LACKS_RETURN instead of CALLEE_LACKS_RETURN.

File summaries

File	Description
src/coreclr/jit/inline.def	Changes LACKS_RETURN to be a callsite-targeted fatal observation with updated wording.
src/coreclr/jit/fginline.cpp	Updates the inline failure recording to use InlineObservation::CALLSITE_LACKS_RETURN.

Review details

• Files reviewed: 2/2 changed files
• Comments generated: 0
• Review effort level: Lite