JIT: remove dead BBJ_RETURN-in-loop assertion in loop cloner#128791
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JIT: remove dead BBJ_RETURN-in-loop assertion in loop cloner#128791AndyAyersMS wants to merge 1 commit into
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optIsLoopClonable contained a DEBUG-only walk that asserted no block in the loop was BBJ_RETURN, plus a stale function comment claiming that fgReturnCount would be bumped on success. There is no code anywhere in loopcloning.cpp that adjusts fgReturnCount (verified by grep), and the assertion is redundant: natural loops in RyuJIT can never contain a BBJ_RETURN block, because FlowGraphNaturalLoop discovery uses only regular CFG back-edges and BBJ_RETURN has no successor that can flow back to a loop header. Verified empirically across 23,712 natural loops from the benchmarks.run_pgo.windows SPMI collection (Tier1 + Tier1-OSR + FullOpts + Tier0-FullOpts, clonable + unclonable) — zero loops contained any BBJ_RETURN block. Drop both the assertion and the stale comment. No behavior change. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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Pull request overview
Removes a stale comment about fgReturnCount and a DEBUG-only assertion that no loop block is BBJ_RETURN from optIsLoopClonable. With EH-loop cloning now enabled by default, BBJ_RETURN blocks can legitimately appear in cloneable loops, and the surrounding context (fgReturnCount is never updated here) makes the comment misleading.
Changes:
- Drop stale
fgReturnCountnote fromoptIsLoopClonableheader comment. - Remove DEBUG
VisitLoopBlocksassertion that rejectedBBJ_RETURNblocks.
jakobbotsch
approved these changes
May 30, 2026
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Loops no longer have returns, so remove some stale comments and checks.