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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).
103 lines
2.3 KiB
C++
103 lines
2.3 KiB
C++
// RUN: %clang_cc1 %s -triple x86_64-apple-darwin10 -emit-llvm -o - | FileCheck %s
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// An extra byte should be allocated for an empty class.
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namespace Test1 {
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// CHECK: %"struct.Test1::A" = type { i8 }
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struct A { } a;
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}
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namespace Test2 {
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// No need to add tail padding here.
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// CHECK: %"struct.Test2::A" = type { ptr, i32 }
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struct A { void *a; int b; } a;
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}
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namespace Test3 {
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// C should have a vtable pointer.
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// CHECK: %"struct.Test3::A" = type <{ ptr, i32, [4 x i8] }>
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struct A { virtual void f(); int a; } a;
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}
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namespace Test4 {
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// Test from PR5589.
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// CHECK: %"struct.Test4::B" = type { %"struct.Test4::A", i16, double }
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// CHECK: %"struct.Test4::A" = type { i32, i8, float }
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struct A {
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int a;
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char c;
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float b;
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};
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struct B : public A {
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short d;
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double e;
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} b;
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}
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namespace Test5 {
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struct A {
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virtual void f();
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char a;
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};
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// CHECK: %"struct.Test5::B" = type { %"struct.Test5::A.base", i8, i8, [5 x i8] }
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struct B : A {
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char b : 1;
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char c;
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} b;
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}
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// PR10912: don't crash
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namespace Test6 {
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template <typename T> class A {
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// If T is complete, IR-gen will want to translate it recursively
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// when translating T*.
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T *foo;
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};
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class B;
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// This causes IR-gen to have an incomplete translation of A<B>
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// sitting around.
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A<B> *a;
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class C {};
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class B : public C {
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// This forces Sema to instantiate A<B>, which triggers a callback
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// to IR-gen. Because of the previous, incomplete translation,
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// IR-gen actually cares, and it immediately tries to complete
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// A<B>'s IR type. That, in turn, causes the translation of B*.
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// B isn't complete yet, but it has a definition, and if we try to
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// compute a record layout for that definition then we'll really
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// regret it later.
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A<B> a;
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};
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// The derived class E and empty base class C are required to
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// provoke the original assertion.
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class E : public B {};
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E *e;
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}
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// Make sure this doesn't crash. (It's okay if we start rejecting it at some
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// point.)
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namespace Test7 {
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#pragma pack (1)
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class A {};
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// CHECK: %"class.Test7::B" = type <{ ptr, i8 }>
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class B {
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virtual ~B();
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A a;
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};
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B test(B b) { return b; }
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#pragma pack ()
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}
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// Shouldn't crash.
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namespace Test8 {
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struct A {};
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struct D { int a; };
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struct B : virtual D, A { };
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struct C : B, A { void f() {} };
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C c;
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}
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