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Do not run optimizations on trivial MIR. #116533

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Merged
merged 1 commit into from
Oct 9, 2023
Merged

Do not run optimizations on trivial MIR. #116533

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9 changes: 9 additions & 0 deletions compiler/rustc_mir_transform/src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -613,6 +613,15 @@ fn inner_optimized_mir(tcx: TyCtxt<'_>, did: LocalDefId) -> Body<'_> {
return body;
}

// If `mir_drops_elaborated_and_const_checked` found that the current body has unsatisfiable
// predicates, it will shrink the MIR to a single `unreachable` terminator.
// More generally, if MIR is a lone `unreachable`, there is nothing to optimize.
if let TerminatorKind::Unreachable = body.basic_blocks[START_BLOCK].terminator().kind
&& body.basic_blocks[START_BLOCK].statements.is_empty()
{
return body;
}

run_optimization_passes(tcx, &mut body);

body
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2 changes: 1 addition & 1 deletion tests/ui/consts/issue-67696-const-prop-ice.rs
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@@ -1,5 +1,5 @@
// check-pass
// compile-flags: --emit=mir,link
// compile-flags: --emit=mir,link -Zmir-opt-level=4
// Checks that we don't ICE due to attempting to run const prop
// on a function with unsatisifable 'where' clauses

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