forked from OSchip/llvm-project
0cb7e7ca0c
The idiom: ``` DeclContext::lookup_result R = DeclContext::lookup(Name); for (auto *D : R) {...} ``` is not safe when in the loop body we trigger deserialization from an AST file. The deserialization can insert new declarations in the StoredDeclsList whose underlying type is a vector. When the vector decides to reallocate its storage the pointer we hold becomes invalid. This patch replaces a SmallVector with an singly-linked list. The current approach stores a SmallVector<NamedDecl*, 4> which is around 8 pointers. The linked list is 3, 5, or 7. We do better in terms of memory usage for small cases (and worse in terms of locality -- the linked list entries won't be near each other, but will be near their corresponding declarations, and we were going to fetch those memory pages anyway). For larger cases: the vector uses a doubling strategy for reallocation, so will generally be between half-full and full. Let's say it's 75% full on average, so there's N * 4/3 + 4 pointers' worth of space allocated currently and will be 2N pointers with the linked list. So we break even when there are N=6 entries and slightly lose in terms of memory usage after that. We suspect that's still a win on average. Thanks to @rsmith! Differential revision: https://reviews.llvm.org/D91524 |
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CPlusPlus | ||
ObjC | ||
RenderScript | ||
CMakeLists.txt |