[PATCH] D129206: [ADT] Use Empty Base Optimization for Allocators

[Nathan James via Phabricator via llvm-commits]

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In D94439 <https://reviews.llvm.org/D94439>, BumpPtrAllocator changed its implementation to use an empty base optimization for the underlying allocator.
This patch builds on that by extending its functionality to more classes as well as enabling the underlying allocator to be a reference type, something not currently possible as you can't derive from a reference.

The main place this sees use is in StringMaps which often use the default MallocAllocator, yet have to pay the size of a pointer for no reason.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D129206

Files:
  llvm/include/llvm/ADT/ScopedHashTable.h
  llvm/include/llvm/ADT/StringMap.h
  llvm/include/llvm/Support/Allocator.h
  llvm/include/llvm/Support/AllocatorBase.h

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