[all-commits] [llvm/llvm-project] d72c8b: [lldb][TypeSystemClang] Create VLAs of explicitly ...

[Michael Buch via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: d72c8b02802c87386f5db3c7de6c79e921618fa3
      https://github.com/llvm/llvm-project/commit/d72c8b02802c87386f5db3c7de6c79e921618fa3
  Author: Michael Buch <michaelbuch12 at gmail.com>
  Date:   2024-07-29 (Mon, 29 Jul 2024)

  Changed paths:
    M lldb/include/lldb/Symbol/SymbolFile.h
    M lldb/source/Plugins/SymbolFile/DWARF/DWARFASTParser.cpp
    M lldb/source/Plugins/SymbolFile/DWARF/DWARFASTParserClang.cpp
    M lldb/source/Plugins/TypeSystem/Clang/TypeSystemClang.cpp
    M lldb/source/Plugins/TypeSystem/Clang/TypeSystemClang.h
    M lldb/test/API/lang/c/struct_types/main.c
    A lldb/test/Shell/SymbolFile/DWARF/vla.cpp

  Log Message:
  -----------
  [lldb][TypeSystemClang] Create VLAs of explicitly 0-size as ConstantArrayType (#100710)

Depends on https://github.com/llvm/llvm-project/pull/100674

Currently, we treat VLAs declared as `int[]` and `int[0]` identically.
I.e., we create them as `IncompleteArrayType`s. However, the
`DW_AT_count` for `int[0]` *does* exist, and is retrievable without an
execution context. This patch decouples the notion of "has 0 elements"
from "has no known `DW_AT_count`".

This aligns with how Clang represents `int[0]` in the AST (it treats it
as a `ConstantArrayType` of 0 size).

This issue was surfaced when adapting LLDB to
https://github.com/llvm/llvm-project/issues/93069. There, the
`__compressed_pair_padding` type has a `char[0]` member. If we
previously got the `__compressed_pair_padding` out of a module (where
clang represents `char[0]` as a `ConstantArrayType`), and try to merge
the AST with one we got from DWARF (where LLDB used to represent
`char[0]` as an `IncompleteArrayType`), the AST structural equivalence
check fails, resulting in silent ASTImporter failures. This manifested
in a failure in `TestNonModuleTypeSeparation.py`.

**Implementation**
1. Adjust `ParseChildArrayInfo` to store the element counts of each VLA
dimension as an `optional<uint64_t>`, instead of a regular `uint64_t`.
So when we pass this down to `CreateArrayType`, we have a better
heuristic for what is an `IncompleteArrayType`.
2. In `TypeSystemClang::GetBitSize`, if we encounter a
`ConstantArrayType` simply return the size that it was created with. If
we couldn't determine the authoritative bound from DWARF during parsing,
we would've created an `IncompleteArrayType`. This ensures that
`GetBitSize` on arrays with `DW_AT_count 0x0` returns `0` (whereas
previously it would've returned a `std::nullopt`, causing that
`FieldDecl` to just get dropped during printing)



To unsubscribe from these emails, change your notification settings at https://github.com/llvm/llvm-project/settings/notifications