codegen: handle OperandValue::Uninit in codegen_return_terminator#159825
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codegen: handle OperandValue::Uninit in codegen_return_terminator#159825glandium wants to merge 1 commit into
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When adding `OperandValue::Uninit` to skip stores for entirely-uninit constants, we missed the `PassMode::Direct | PassMode::Pair` branch of `codegen_return_terminator`, which called `immediate_or_packed_pair` unconditionally. A function directly returning an all-uninit value (e.g. `MaybeUninit::uninit()`) would hit that branch and ICE in `OperandRef::immediate`, as reported against tokio and reduced by tmiasko.
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Jul 24, 2026
| pub fn f() -> MaybeUninit<*const ()> { | ||
| // CHECK: start: | ||
| // CHECK-NEXT: ret ptr undef | ||
| MaybeUninit::uninit() |
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nit: const { MaybeUninit::uninit() } would avoid dependency on MIR optimizations, i.e., compile-flags: -Copt-level=2
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Fixes #159815.
#157797 added
OperandValue::Uninitto skip stores for entirely-uninit constants, but missed thePassMode::Direct | PassMode::Pairbranch ofcodegen_return_terminator, which calledimmediate_or_packed_pairunconditionally. A function directly returning an all-uninit value (e.g.MaybeUninit::uninit()) would hit that branch and ICE inOperandRef::immediate, as reported against tokio and reduced by tmiasko.