4497ec293a
This is a follow-up from the conversation starting at https://github.com/llvm/llvm-project/pull/93809#issuecomment-2173729801 The root problem that motivated the change are external AST sources that compute `ASTRecordLayout`s themselves instead of letting Clang compute them from the AST. One such example is LLDB using DWARF to get the definitive offsets and sizes of C++ structures. Such layouts should be considered correct (modulo buggy DWARF), but various assertions and lowering logic around the `CGRecordLayoutBuilder` relies on the AST having `[[no_unique_address]]` attached to them. This is a layout-altering attribute which is not encoded in DWARF. This causes us LLDB to trip over the various LLVM<->Clang layout consistency checks. There has been precedent for avoiding such layout-altering attributes from affecting lowering with externally-provided layouts (e.g., packed structs). This patch proposes to replace the `isZeroSize` checks in `CGRecordLayoutBuilder` (which roughly means "empty field with [[no_unique_address]]") with checks for `CodeGen::isEmptyField`/`CodeGen::isEmptyRecord`. **Details** The main strategy here was to change the `isZeroSize` check in `CGRecordLowering::accumulateFields` and `CGRecordLowering::accumulateBases` to use the `isEmptyXXX` APIs instead, preventing empty fields from being added to the `Members` and `Bases` structures. The rest of the changes fall out from here, to prevent lookups into these structures (for field numbers or base indices) from failing. Added `isEmptyRecordForLayout` and `isEmptyFieldForLayout` (open to better naming suggestions). The main difference to the existing `isEmptyRecord`/`isEmptyField` APIs, is that the `isEmptyXXXForLayout` counterparts don't have special treatment for `unnamed bitfields`/arrays and also treat fields of empty types as if they had `[[no_unique_address]]` (i.e., just like the `AsIfNoUniqueAddr` in `isEmptyField` does).
20 lines
726 B
C
20 lines
726 B
C
// RUN: %clang_cc1 %s -emit-llvm -triple x86_64-linux-gnu -o - | FileCheck %s --check-prefixes=CHECK,EMPTY
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// RUN: %clang_cc1 %s -emit-llvm -triple x86_64-windows-msvc -o - | FileCheck %s --check-prefixes=CHECK,EMPTY-MSVC
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// PR4390
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struct sysfs_dirent {
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union { struct sysfs_elem_dir { int x; } s_dir; };
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unsigned short s_mode;
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};
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struct sysfs_dirent sysfs_root = { {}, 16877 };
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// CHECK: @sysfs_root = {{.*}}global %struct.sysfs_dirent { %union.anon zeroinitializer, i16 16877 }
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struct Foo {
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union { struct empty {} x; };
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unsigned short s_mode;
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};
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struct Foo foo = { {}, 16877 };
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// EMPTY: @foo = {{.*}}global %struct.Foo { i16 16877 }
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// EMPTY-MSVC: @foo = {{.*}}global %struct.Foo { [4 x i8] undef, i16 16877 }
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