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Auto merge of #65172 - tanriol:explain_borrow-use-context-dominators, r=nagisa

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use precalculated dominators in explain_borrow

This looks like the only place calculating dominators from the MIR body every time instead of using the ones stored on the `MirBorrowckCtxt`. For example, in rust-lang/rust#65131 a big generated function with a number of borrowck errors takes a few hours(!) recalculating the dominators while explaining the errors.

I don't know enough about this part of rustc codebase to know for sure that this change is correct, but no tests seem to fail as a result of this change in local testing.
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bors 2019-10-16 12:49:49 +00:00
commit 53aca553ec
1 changed files with 1 additions and 1 deletions
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src/librustc_mir/borrow_check/nll/explain_borrow/mod.rs
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@ -458,7 +458,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
/// True if an edge `source -> target` is a backedge -- in other words, if the target
/// dominates the source.
fn is_back_edge(&self, source: Location, target: Location) -> bool {
target.dominates(source, &self.body.dominators())
target.dominates(source, &self.dominators)
}
/// Determine how the borrow was later used.