Author: Erich Keane Date: 2026-04-02T06:00:23-07:00 New Revision: 710d647586a4accef82a72c32c45a9cc77bbef53
URL: https://github.com/llvm/llvm-project/commit/710d647586a4accef82a72c32c45a9cc77bbef53 DIFF: https://github.com/llvm/llvm-project/commit/710d647586a4accef82a72c32c45a9cc77bbef53.diff LOG: [CIR] Implement 'null' function-pointer vtable entries (#190013) This functionality is described in the Itanium C++ABI 2.5.2 (and is also where the test comes from). See also VTableBuilder.cpp's documentation on the declaration of IsOverriderUsed for further details. However, the explaination is: When B and C are declared, A is a primary base in each case, so although vcall offsets are allocated in the A-in-B and A-in-C vtables, no this adjustment is required and no thunk is generated. However, inside D objects, A is no longer a primary base of C, so if we allowed calls to C::f() to use the copy of A's vtable in the C subobject, we would need to adjust this from C* to B::A*, which would require a third-party thunk. Since we require that a call to C::f() first convert to A*, C-in-D's copy of A's vtable is never referenced, so this is not necessary. The short of that is: there is no way to call these, so we just emit a nullptr rather than the required thunk. Added: clang/test/CIR/CodeGen/vtable-null-func-ptr.cpp Modified: clang/lib/CIR/CodeGen/CIRGenVTables.cpp Removed: ################################################################################ diff --git a/clang/lib/CIR/CodeGen/CIRGenVTables.cpp b/clang/lib/CIR/CodeGen/CIRGenVTables.cpp index cdc83a3ede3c7..ceaceb2ffb66a 100644 --- a/clang/lib/CIR/CodeGen/CIRGenVTables.cpp +++ b/clang/lib/CIR/CodeGen/CIRGenVTables.cpp @@ -146,8 +146,7 @@ mlir::Attribute CIRGenVTables::getVTableComponent( switch (component.getKind()) { case VTableComponent::CK_UnusedFunctionPointer: - cgm.errorNYI("getVTableComponent: UnusedFunctionPointer"); - return mlir::Attribute(); + return builder.getConstNullPtrAttr(builder.getUInt8PtrTy()); case VTableComponent::CK_VCallOffset: return builder.getConstPtrAttr(builder.getUInt8PtrTy(), diff --git a/clang/test/CIR/CodeGen/vtable-null-func-ptr.cpp b/clang/test/CIR/CodeGen/vtable-null-func-ptr.cpp new file mode 100644 index 0000000000000..a0f9192e68801 --- /dev/null +++ b/clang/test/CIR/CodeGen/vtable-null-func-ptr.cpp @@ -0,0 +1,30 @@ +// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -std=c++20 -fclangir -emit-cir -mmlir -mlir-print-ir-before=cir-cxxabi-lowering %s -o %t.cir 2> %t-before.cir +// RUN: FileCheck --input-file=%t-before.cir -check-prefix=CIR %s +// RUN: FileCheck --input-file=%t.cir --check-prefix=CIR %s +// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -std=c++20 -fclangir -emit-llvm %s -o %t-cir.ll +// RUN: FileCheck --input-file=%t-cir.ll --check-prefix=LLVM %s +// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -std=c++20 -emit-llvm %s -o %t.ll +// RUN: FileCheck --input-file=%t.ll --check-prefix=LLVM %s + + +// This is an example right out of the itanium ABI for a 'null' function +// pointer. +struct A { virtual void f(); }; +struct B : virtual public A { int i; }; +struct C : virtual public A { int j; }; +struct D : public B, public C { + virtual void d(); +}; +void D::d() {} + +// CIR: cir.global {{.*}}@_ZTV1D = #cir.vtable<{#cir.const_array<[#cir.ptr<null> : !cir.ptr<!u8i>, #cir.ptr<null> : !cir.ptr<!u8i>, #cir.ptr<null> : !cir.ptr<!u8i>, #cir.global_view<@_ZTI1D> : !cir.ptr<!u8i>, #cir.global_view<@_ZN1A1fEv> : !cir.ptr<!u8i>, #cir.global_view<@_ZN1D1dEv> : !cir.ptr<!u8i>]> : !cir.array<!cir.ptr<!u8i> x 6>, #cir.const_array<[#cir.ptr<-16 : i64> : !cir.ptr<!u8i>, #cir.ptr<-16 : i64> : !cir.ptr<!u8i>, #cir.ptr<-16 : i64> : !cir.ptr<!u8i>, #cir.global_view<@_ZTI1D> : !cir.ptr<!u8i>, #cir.ptr<null> : !cir.ptr<!u8i>]> : !cir.array<!cir.ptr<!u8i> x 5>}> +// +// LLVM: @_ZTV1D = {{.*}}{ [6 x ptr], [5 x ptr] } { [6 x ptr] [ptr null, ptr null, ptr null, ptr @_ZTI1D, ptr @_ZN1A1fEv, ptr @_ZN1D1dEv], [5 x ptr] [ptr inttoptr (i64 -16 to ptr), ptr inttoptr (i64 -16 to ptr), ptr inttoptr (i64 -16 to ptr), ptr @_ZTI1D, ptr null] }, align 8 +// +// CIR: cir.global {{.*}}@_ZTC1D0_1B = #cir.vtable<{#cir.const_array<[#cir.ptr<null> : !cir.ptr<!u8i>, #cir.ptr<null> : !cir.ptr<!u8i>, #cir.ptr<null> : !cir.ptr<!u8i>, #cir.global_view<@_ZTI1B> : !cir.ptr<!u8i>, #cir.global_view<@_ZN1A1fEv> : !cir.ptr<!u8i>]> : !cir.array<!cir.ptr<!u8i> x 5>}> + +// LLVM: @_ZTC1D0_1B = {{.*}}{ [5 x ptr] } { [5 x ptr] [ptr null, ptr null, ptr null, ptr @_ZTI1B, ptr @_ZN1A1fEv] }, align 8 +// +// CIR: cir.global {{.*}}@_ZTC1D16_1C = #cir.vtable<{#cir.const_array<[#cir.ptr<-16 : i64> : !cir.ptr<!u8i>, #cir.ptr<-16 : i64> : !cir.ptr<!u8i>, #cir.ptr<null> : !cir.ptr<!u8i>, #cir.global_view<@_ZTI1C> : !cir.ptr<!u8i>, #cir.ptr<null> : !cir.ptr<!u8i>]> : !cir.array<!cir.ptr<!u8i> x 5>, #cir.const_array<[#cir.ptr<null> : !cir.ptr<!u8i>, #cir.ptr<16 : i64> : !cir.ptr<!u8i>, #cir.global_view<@_ZTI1C> : !cir.ptr<!u8i>, #cir.global_view<@_ZN1A1fEv> : !cir.ptr<!u8i>]> : !cir.array<!cir.ptr<!u8i> x 4>}> +// +// LLVM: @_ZTC1D16_1C = {{.*}}{ [5 x ptr], [4 x ptr] } { [5 x ptr] [ptr inttoptr (i64 -16 to ptr), ptr inttoptr (i64 -16 to ptr), ptr null, ptr @_ZTI1C, ptr null], [4 x ptr] [ptr null, ptr inttoptr (i64 16 to ptr), ptr @_ZTI1C, ptr @_ZN1A1fEv] }, align 8 _______________________________________________ cfe-commits mailing list [email protected] https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
