Split dummy-idx node to fix expand_givens DFS #31442
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r? @arielb1 (rust_highfive has picked a reviewer for you, use r? to override) |
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I would just split |
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I found that bug independently (that's what I deserve for going bug-hunting with such a huge notification backlog), and it was the same givens bug. |
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Ah yeah splitting dummy_idx sounds better in nearly every way. I'll do that tomorrow |
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Also, this fix is so simple that I'm nominating it to be merged to beta as well. |
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…odes. Why do this: The RegionGraph representation previously conflated all of the non-variable regions (i.e. the concrete regions such as lifetime parameters to the current function) into a single dummy node. A single dummy node leads DFS on a graph `'a -> '_#1 -> '_#0 -> 'b` to claim that `'_#1` is reachable from `'_#0` (due to `'a` and `'b` being conflated in the graph representation), which is incorrect (and can lead to soundness bugs later on in compilation, see rust-lang#30438). Splitting the dummy node ensures that DFS will never introduce new ancestor relationships between nodes for variable regions in the graph.
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@bors r+ |
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📌 Commit 77c8850 has been approved by |
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Feb 8, 2016
…g-expand-givens-dfs, r=nikomatsakis Split dummy-idx node to fix expand_givens DFS (Much more detail in commit comments.) Fix #30438.
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We don't normally backport random fixes, but this seems like both a severe problem (unsoundness and a kind of random one) and a simple fix, so go for it. |
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Split dummy-idx node to fix expand_givens DFS
(Much more detail in commit comments.)
Fix #30438.