dzhidzhoev added inline comments.
================
Comment at: clang/lib/CodeGen/CGRecordLayoutBuilder.cpp:370
+ const auto StorageAlignment = getAlignment(StorageType);
+ if (LayoutSize % StorageAlignment || Layout.getDataSize() % StorageAlignment)
Packed = true;
----------------
efriedma wrote:
> Should this be `if (Layout.getSize() % StorageAlignment ||
> Layout.getDataSize() % StorageAlignment)`? The dependency on
> isNoUniqueAddress is a bit confusing.
For base class subobjects, base class DataSize is used to compute the whole
object size in RecordLayoutBuilder.cpp, and base subobject LLVM type (with
".base" suffix) is computed in addition to standard layout LLVM type in
CGRecordLayoutBuilder.cpp.
Currently, both base subobject and standard layout LLVM types of the same class
are supposed to agree on packedness, as stated in bb51300970b7. Thus, if one is
packed, both are marked as packed, as done in
CGRecordLowering::determinePacked.
For data members of class/struct type, declared with [[no_unique_address]]
attribute, DataSize is used to compute the whole object size in
RecordLayoutBuilder.cpp, but standard layout LLVM type is used to represent the
field in the whole class's LLVM type.
This patch proposes to use the base subobject LLVM type instead of the default
LLVM type of a class to lay out a no_unique_address member of this class type.
Nextly, the patch proposes to create an unpadded LLVM type for unions, in
addition to the default LLVM type. It is used to lay out the union members
having no_unique_address attribute. Existing code for creating base subobject
layout of classes are reused for unions, therefore, packedness of
potentially-overlapping union LLVM type and of default union LLVM types must
agree as well as for classes.
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D139741/new/
https://reviews.llvm.org/D139741
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