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Add some comments to generator clone shim code

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Andrew Cann 2022-04-10 14:04:44 +08:00 committed by Charles Lew
parent 1bc9453aa8
commit 543023c249
1 changed files with 12 additions and 0 deletions
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12
compiler/rustc_mir_transform/src/shim.rs
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@ -475,7 +475,18 @@ impl<'tcx> CloneShimBuilder<'tcx> {
where where
I: IntoIterator<Item = Ty<'tcx>>, I: IntoIterator<Item = Ty<'tcx>>,
{ {
// For an iterator of length n, create 2*n + 1 blocks.
for (i, ity) in tys.into_iter().enumerate() { for (i, ity) in tys.into_iter().enumerate() {
// Each iteration creates two blocks, referred to here as block 2*i and block 2*i + 1.
//
// Block 2*i attempts to clone the field. If successful it branches to 2*i + 2 (the
// next clone block). If unsuccessful it branches to the previous unwind block, which
// is initially the `unwind` argument passed to this function.
//
// Block 2*i + 1 is the unwind block for this iteration. It drops the cloned value
// created by block 2*i. We store this block in `unwind` so that the next clone block
// will unwind to it if cloning fails.
let field = Field::new(i); let field = Field::new(i);
let src_field = self.tcx.mk_place_field(src, field, ity); let src_field = self.tcx.mk_place_field(src, field, ity);
@ -491,6 +502,7 @@ impl<'tcx> CloneShimBuilder<'tcx> {
); );
unwind = next_unwind; unwind = next_unwind;
} }
// If all clones succeed then we end up here.
self.block(vec![], TerminatorKind::Goto { target }, false); self.block(vec![], TerminatorKind::Goto { target }, false);
unwind unwind
} }