diff options
| -rw-r--r-- | compiler/rustc_mir_transform/src/shim.rs | 12 |
1 files changed, 12 insertions, 0 deletions
diff --git a/compiler/rustc_mir_transform/src/shim.rs b/compiler/rustc_mir_transform/src/shim.rs index 3a43932f50c..f5083438b0c 100644 --- a/compiler/rustc_mir_transform/src/shim.rs +++ b/compiler/rustc_mir_transform/src/shim.rs @@ -475,7 +475,18 @@ impl<'tcx> CloneShimBuilder<'tcx> { where I: IntoIterator<Item = Ty<'tcx>>, { + // For an iterator of length n, create 2*n + 1 blocks. 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 src_field = self.tcx.mk_place_field(src, field, ity); @@ -491,6 +502,7 @@ impl<'tcx> CloneShimBuilder<'tcx> { ); unwind = next_unwind; } + // If all clones succeed then we end up here. self.block(vec![], TerminatorKind::Goto { target }, false); unwind } |