[llvm] [Allocator] Keep bump pointer at a minimum alignment (PR #203718)

[Fangrui Song via llvm-commits]

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@@ -388,7 +400,11 @@ using BumpPtrAllocator = BumpPtrAllocatorImpl<>;
 /// This allows calling the destructor in DestroyAll() and when the allocator is
 /// destroyed.
 template <typename T> class SpecificBumpPtrAllocator {
-  BumpPtrAllocator Allocator;
+  // DestroyAll() walks objects at a fixed sizeof(T) stride, so it needs tight
+  // packing: MinAlign=1 disables the default size rounding.
+  using BumpPtrAllocatorTy =
+      BumpPtrAllocatorImpl<MallocAllocator, 4096, 4096, 128, /*MinAlign=*/1>;
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MaskRay wrote:

alignof(T) is indeed better. Switched to `std::min(alignof(T), alignof(std::max_align_t))` since fresh slabs don't provide an alignment larger than `alignof(std::max_align_t)`

https://github.com/llvm/llvm-project/pull/203718