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Split the chunk header into F14ChunkHeader; the empty chunk is a real header object (#2741) - #2741
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@DenisYaroshevskiy has exported this pull request. If you are a Meta employee, you can view the originating Diff in D130938727. |
… header object (meta#2741) Summary: The 16-byte chunk header (`tags_`, `control_`, `outboundOverflowCount_` and the overflow constants) moves into a non-template base `F14ChunkHeader`; `F14Chunk<Item>` derives from it. The empty instance becomes a single `inline constexpr F14ChunkHeader kF14EmptyChunkHeader`, and `F14Table::chunks_` points to the header. - `F14Table::chunks()` (fancy `ChunkPtr`) and `chunksToAddress()` (raw `Chunk*`) `static_cast` down to `F14Chunk<Item>`; the former `std::to_address(chunks_)` uses become `chunksToAddress()`. - `F14EmptyTagVector` / `getF14EmptyTagVector()` go away; `isEmptyInstance` / `capacityScale` read the chunk's own fields instead of `reinterpret_cast`ing the chunk to the tag vector. - `PackedChunkItemPtr` gets a defaulted default constructor and default member initializers (null); `packedBegin_` is initialized with `{}` instead of `ItemIter{}.pack()`. - The gdb pretty printer casts `chunks_` to the table's `Chunk` type. No `reinterpret_cast` of the empty instance remains. This prepares for `constexpr` default construction (next diff), which needs the empty-chunk address to be a constant expression. Reviewed By: yfeldblum Differential Revision: D130938727
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This pull request has been merged in e582654. |
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Summary:
The 16-byte chunk header (
tags_,control_,outboundOverflowCount_and the overflow constants) moves into a non-template baseF14ChunkHeader;F14Chunk<Item>derives from it. The empty instance becomes a singleinline constexpr F14ChunkHeader kF14EmptyChunkHeader, andF14Table::chunks_points to the header.F14Table::chunks()(fancyChunkPtr) andchunksToAddress()(rawChunk*)static_castdown toF14Chunk<Item>; the formerstd::to_address(chunks_)uses becomechunksToAddress().F14EmptyTagVector/getF14EmptyTagVector()go away;isEmptyInstance/capacityScaleread the chunk's own fields instead ofreinterpret_casting the chunk to the tag vector.PackedChunkItemPtrgets a defaulted default constructor and default member initializers (null);packedBegin_is initialized with{}instead ofItemIter{}.pack().chunks_to the table'sChunktype.No
reinterpret_castof the empty instance remains. This prepares forconstexprdefault construction (next diff), which needs the empty-chunk address to be a constant expression.Reviewed By: yfeldblum
Differential Revision: D130938727