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).
29 lines
737 B
C++
29 lines
737 B
C++
// RUN: %clang_cc1 -triple i686-linux-gnu %s -emit-llvm -o - | FileCheck %s
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class A {
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// append has to have the same prototype as fn1 to tickle the bug.
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void (*append)(A *);
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};
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class B {};
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class D;
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// C has to be non-C++98 POD with available tail padding, making the LLVM base
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// type differ from the complete LLVM type.
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class C {
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// This member creates a circular LLVM type reference to %class.D.
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D *m_group;
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B changeListeners;
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};
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class D : C {};
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A p1;
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C p2;
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D p3;
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// We end up using an opaque type for 'append' to avoid circular references.
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// CHECK: %class.A = type { ptr }
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// CHECK: %class.C = type <{ ptr, [4 x i8] }>
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// CHECK: %class.D = type { %class.C.base, [3 x i8] }
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// CHECK: %class.C.base = type <{ ptr, i8 }>
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