[CIR][CIRGen] Support a defined pure virtual destructor (#825)

This is permitted by the language, and IRGen emits traps for destructors
other than the base object destructor. Make CIRGen follow suit.

Author: smeenai

clang/lib/CIR/CodeGen/CIRGenClass.cpp

@@ -1109,7 +1109,14 @@ void CIRGenFunction::buildDestructorBody(FunctionArgList &Args) {
   // in fact emit references to them from other compilations, so emit them
   // as functions containing a trap instruction.
   if (DtorType != Dtor_Base && Dtor->getParent()->isAbstract()) {
-    llvm_unreachable("NYI");
+    SourceLocation Loc =
+        Dtor->hasBody() ? Dtor->getBody()->getBeginLoc() : Dtor->getLocation();
+    builder.create<mlir::cir::TrapOp>(getLoc(Loc));
+    // The corresponding clang/CodeGen logic clears the insertion point here,
+    // but MLIR's builder requires a valid insertion point, so we create a dummy
+    // block (since the trap is a block terminator).
+    builder.createBlock(builder.getBlock()->getParent());
+    return;
   }
 
   Stmt *Body = Dtor->getBody();

clang/test/CIR/CodeGen/defined-pure-virtual-func.cpp

@@ -0,0 +1,58 @@
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -fclangir -emit-cir %s -o %t.cir
+// RUN: FileCheck --input-file=%t.cir %s
+
+// Pure virtual functions are allowed to be defined, but the vtable should still
+// point to __cxa_pure_virtual instead of the definition. For destructors, the
+// base object destructor (which is not included in the vtable) should be
+// defined as usual. The complete object destructors and deleting destructors
+// should contain a trap, and the vtable entries for them should point to
+// __cxa_pure_virtual.
+class C {
+  C();
+  virtual ~C() = 0;
+  virtual void pure() = 0;
+};
+
+C::C() = default;
+C::~C() = default;
+void C::pure() {}
+
+// CHECK: @_ZTV1C = #cir.vtable<{#cir.const_array<[#cir.ptr<null> : !cir.ptr<!u8i>, #cir.global_view<@_ZTI1C> : !cir.ptr<!u8i>
+// complete object destructor (D1)
+// CHECK-SAME: #cir.global_view<@__cxa_pure_virtual> : !cir.ptr<!u8i>,
+// deleting destructor (D0)
+// CHECK-SAME: #cir.global_view<@__cxa_pure_virtual> : !cir.ptr<!u8i>,
+// C::pure
+// CHECK-SAME: #cir.global_view<@__cxa_pure_virtual> : !cir.ptr<!u8i>]>
+
+// The base object destructor should be emitted as normal.
+// CHECK-LABEL: cir.func @_ZN1CD2Ev(%arg0: !cir.ptr<!ty_C> loc({{[^)]+}})) {{.*}} {
+// CHECK-NEXT:    %0 = cir.alloca !cir.ptr<!ty_C>, !cir.ptr<!cir.ptr<!ty_C>>, ["this", init] {alignment = 8 : i64}
+// CHECK-NEXT:    cir.store %arg0, %0 : !cir.ptr<!ty_C>, !cir.ptr<!cir.ptr<!ty_C>>
+// CHECK-NEXT:    %1 = cir.load %0 : !cir.ptr<!cir.ptr<!ty_C>>, !cir.ptr<!ty_C>
+// CHECK-NEXT:    cir.return
+// CHECK-NEXT:  }
+
+// The complete object destructor should trap.
+// CHECK-LABEL: cir.func @_ZN1CD1Ev(%arg0: !cir.ptr<!ty_C> loc({{[^)]+}})) {{.*}} {
+// CHECK-NEXT:    %0 = cir.alloca !cir.ptr<!ty_C>, !cir.ptr<!cir.ptr<!ty_C>>, ["this", init] {alignment = 8 : i64}
+// CHECK-NEXT:    cir.store %arg0, %0 : !cir.ptr<!ty_C>, !cir.ptr<!cir.ptr<!ty_C>>
+// CHECK-NEXT:    %1 = cir.load %0 : !cir.ptr<!cir.ptr<!ty_C>>, !cir.ptr<!ty_C>
+// CHECK-NEXT:    cir.trap
+// CHECK-NEXT:  }
+
+// The deleting destructor should trap.
+// CHECK-LABEL: cir.func @_ZN1CD0Ev(%arg0: !cir.ptr<!ty_C> loc({{[^)]+}})) {{.*}} {
+// CHECK-NEXT:    %0 = cir.alloca !cir.ptr<!ty_C>, !cir.ptr<!cir.ptr<!ty_C>>, ["this", init] {alignment = 8 : i64}
+// CHECK-NEXT:    cir.store %arg0, %0 : !cir.ptr<!ty_C>, !cir.ptr<!cir.ptr<!ty_C>>
+// CHECK-NEXT:    %1 = cir.load %0 : !cir.ptr<!cir.ptr<!ty_C>>, !cir.ptr<!ty_C>
+// CHECK-NEXT:    cir.trap
+// CHECK-NEXT:  }
+
+// C::pure should be emitted as normal.
+// CHECK-LABEL: cir.func @_ZN1C4pureEv(%arg0: !cir.ptr<!ty_C> loc({{[^)]+}})) {{.*}} {
+// CHECK-NEXT:    %0 = cir.alloca !cir.ptr<!ty_C>, !cir.ptr<!cir.ptr<!ty_C>>, ["this", init] {alignment = 8 : i64}
+// CHECK-NEXT:    cir.store %arg0, %0 : !cir.ptr<!ty_C>, !cir.ptr<!cir.ptr<!ty_C>>
+// CHECK-NEXT:    %1 = cir.load %0 : !cir.ptr<!cir.ptr<!ty_C>>, !cir.ptr<!ty_C>
+// CHECK-NEXT:    cir.return
+// CHECK-NEXT:  }