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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|---|---|---|
| .. | ||
| AppleObjCClassDescriptorV2.cpp | ||
| AppleObjCClassDescriptorV2.h | ||
| AppleObjCDeclVendor.cpp | ||
| AppleObjCDeclVendor.h | ||
| AppleObjCRuntime.cpp | ||
| AppleObjCRuntime.h | ||
| AppleObjCRuntimeV1.cpp | ||
| AppleObjCRuntimeV1.h | ||
| AppleObjCRuntimeV2.cpp | ||
| AppleObjCRuntimeV2.h | ||
| AppleObjCTrampolineHandler.cpp | ||
| AppleObjCTrampolineHandler.h | ||
| AppleObjCTypeEncodingParser.cpp | ||
| AppleObjCTypeEncodingParser.h | ||
| AppleThreadPlanStepThroughObjCTrampoline.cpp | ||
| AppleThreadPlanStepThroughObjCTrampoline.h | ||
| CMakeLists.txt | ||