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Avoid a heap allocation in TerminatorEdges::AssignOnReturn [-0.13%] #64

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Avoid a heap allocation in TerminatorEdges::AssignOnReturn [-0.13%] #64

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8 changes: 6 additions & 2 deletions compiler/rustc_middle/src/mir/terminator.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -689,7 +689,11 @@ pub enum TerminatorEdges<'mir, 'tcx> {
Double(BasicBlock, BasicBlock),
/// Special action for `Yield`, `Call` and `InlineAsm` terminators.
AssignOnReturn {
return_: Box<[BasicBlock]>,
// Inline storage avoids a heap allocation on the very common `Call`
// terminator (which has at most one return target) and on `Yield`
// (at most two), both of which are visited repeatedly by every
// dataflow analysis. `InlineAsm` with many targets still spills.
return_: SmallVec<[BasicBlock; 2]>,
/// The cleanup block, if it exists.
cleanup: Option<BasicBlock>,
place: CallReturnPlaces<'mir, 'tcx>,
Expand Down Expand Up @@ -783,7 +787,7 @@ impl<'tcx> TerminatorKind<'tcx> {
ref targets,
unwind,
} => TerminatorEdges::AssignOnReturn {
return_: targets.to_owned(),
return_: targets.iter().copied().collect(),
cleanup: unwind.cleanup_block(),
place: CallReturnPlaces::InlineAsm(operands),
},
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