Nicholas Nethercote f778bdefdd Avoid repeated HashMap lookups in opt_normalize_projection_type. ... There is a hot path through `opt_normalize_projection_type`: - `try_start` does a cache lookup (#1). - The result is a `NormalizedTy`. - There are no unresolved type vars, so we call `complete`. - `complete` does *another* cache lookup (#2), then calls `SnapshotMap::insert`. - `insert` does *another* cache lookup (#3), inserting the same value that's already in the cache. This patch optimizes this hot path by introducing `complete_normalized`, for use when the value is known in advance to be a `NormalizedTy`. It always avoids lookup #2. Furthermore, if the `NormalizedTy`'s obligations are empty (the common case), we know that lookup #3 would be a no-op, so we avoid it, while inserting a Noop into the `SnapshotMap`'s undo log.		2018-05-17 09:34:20 +10:00
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mod.rs	Avoid repeated HashMap lookups in opt_normalize_projection_type.	2018-05-17 09:34:20 +10:00
test.rs	add a snapshottable hashmap	2016-05-31 19:44:05 -04:00