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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).
27 lines
1.0 KiB
C++
27 lines
1.0 KiB
C++
// RUN: %clang_cc1 %s -emit-llvm -o - -triple x86_64-linux-gnu | FileCheck %s
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struct A {
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A(const char *);
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};
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// CHECK: @arr ={{.*}} global [3 x %struct.S] zeroinitializer
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// CHECK: @.str = {{.*}}constant [6 x i8] c"hello\00"
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// CHECK: @.str.1 = {{.*}}constant [6 x i8] c"world\00"
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// CHECK: @.str.2 = {{.*}}constant [8 x i8] c"goodbye\00"
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struct S {
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int n;
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A s;
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} arr[] = {
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{ 0, "hello" },
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{ 1, "world" },
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{ 2, "goodbye" }
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};
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// CHECK: store i32 0, ptr @arr
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// CHECK: call void @_ZN1AC1EPKc(ptr {{[^,]*}} getelementptr inbounds (i8, ptr @arr, i64 4), ptr noundef @.str)
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// CHECK: store i32 1, ptr getelementptr inbounds (%struct.S, ptr @arr, i64 1)
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// CHECK: call void @_ZN1AC1EPKc(ptr {{[^,]*}} getelementptr inbounds (i8, ptr getelementptr inbounds (%struct.S, ptr @arr, i64 1), i64 4), ptr noundef @.str.1)
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// CHECK: store i32 2, ptr getelementptr inbounds (%struct.S, ptr @arr, i64 2)
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// CHECK: call void @_ZN1AC1EPKc(ptr {{[^,]*}} getelementptr inbounds (i8, ptr getelementptr inbounds (%struct.S, ptr @arr, i64 2), i64 4), ptr noundef @.str.2)
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