[TailCall] Fix intrinsic and unreachable calls - #9111
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Late in the development of the TailCall pass, we removed a run of DCE in a nested pass runner. It turns out that had been load bearing, because without it TailCall could optimize unreachable calls whose callee return types did not match the caller return type, producing invalid IR. Fix the bug by not optimizing unreachable calls, leaving them for a separate DCE pass to clean up instead. Also fix the lowering of call.without.effects when it is used as a tail call. Previously intrinsic lowering would turn such a tail call into a normal call, again producing invalid IR because the normal call is not unreachable and is not valid in all the places a tail call would be.
tlively
requested review from
aheejin and
kripken
and removed request for
a team
September 17, 2026 04:17
kripken
reviewed
Sep 17, 2026
kripken
approved these changes
Sep 17, 2026
Co-authored-by: Alon Zakai <azakai@google.com>
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Late in the development of the TailCall pass, we removed a run of DCE in a nested pass runner. It turns out that had been load bearing, because without it TailCall could optimize unreachable calls whose callee return types did not match the caller return type, producing invalid IR. Fix the bug by not optimizing unreachable calls, leaving them for a separate DCE pass to clean up instead.
Also fix the lowering of call.without.effects when it is used as a tail call. Previously intrinsic lowering would turn such a tail call into a normal call, again producing invalid IR because the normal call is not unreachable and is not valid in all the places a tail call would be.