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Properly re-use def path hash in incremental mode

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Fixes #79661

In incremental compilation mode, we update a `DefPathHash -> DefId`
mapping every time we create a `DepNode` for a foreign `DefId`.
This mapping is written out to the on-disk incremental cache, and is
read by the next compilation session to allow us to lazily decode
`DefId`s.

When we decode a `DepNode` from the current incremental cache, we need
to ensure that any previously-recorded `DefPathHash -> DefId` mapping
gets recorded in the new mapping that we write out. However, PR #74967
didn't do this in all cases, leading to us being unable to decode a
`DefPathHash` in certain circumstances.

This PR refactors some of the code around `DepNode` deserialization to
prevent this kind of mistake from happening again.
This commit is contained in:
Aaron Hill 2020-12-04 18:37:21 -05:00
parent 3ff10e74a7
commit c2946402ff
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6 changed files with 79 additions and 20 deletions
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2
compiler/rustc_middle/src/ty/query/mod.rs
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@ -220,7 +220,7 @@ pub(crate) fn try_load_from_on_disk_cache<'tcx>(tcx: TyCtxt<'tcx>, dep_node: &De
.map(|c| c.is_green())
.unwrap_or(false));
let key = <query_keys::$name<'tcx> as DepNodeParams<TyCtxt<'_>>>::recover(tcx, dep_node).unwrap();
let key = <query_keys::$name<'tcx> as DepNodeParams<TyCtxt<'_>>>::recover(tcx, dep_node).unwrap_or_else(|| panic!("Failed to recover key for {:?} with hash {}", dep_node, dep_node.hash));
if queries::$name::cache_on_disk(tcx, &key, None) {
let _ = tcx.$name(key);
}