[CodeGen] Fix TBAA info for accesses to members of base classes

[kosarev]

Summary

Resolves:
Bug 35724 - regression (r315984): fatal error: error in backend: Broken function found (Did not see access type in access path!)
https://bugs.llvm.org/show_bug.cgi?id=35724

[rjmccall]

Ok.

lib/CodeGen/CGExpr.cpp

if (const CastExpr *CE = dyn_cast<CastExpr>(E)) {
 
     // Array-to-pointer decay.
     case CK_ArrayToPointerDecay:
       return EmitArrayToPointerDecay(CE->getSubExpr(), BaseInfo, TBAAInfo);
 
     // Derived-to-base conversions.
     case CK_UncheckedDerivedToBase:
     case CK_DerivedToBase: {
-      Address Addr = EmitPointerWithAlignment(CE->getSubExpr(), BaseInfo,
-                                              TBAAInfo);
+      // TODO: Support accesses to members of base classes in TBAA. For now, we
+      // conservatively pretend that the complete object is of the base class
+      // type.
+      if (TBAAInfo)
+        *TBAAInfo = CGM.getTBAAAccessInfo(E->getType());
+      Address Addr = EmitPointerWithAlignment(CE->getSubExpr(), BaseInfo);
       auto Derived = CE->getSubExpr()->getType()->getPointeeCXXRecordDecl();
       return GetAddressOfBaseClass(Addr, Derived,
                                    CE->path_begin(), CE->path_end(),
                                    ShouldNullCheckClassCastValue(CE),
                                    CE->getExprLoc());
     }
 
     // TODO: Is there any reason to treat base-to-derived conversions

test/CodeGen/tbaa-base.cpp

+// RUN: %clang_cc1 -triple x86_64-linux-gnu -O1 %s -emit-llvm -o - | FileCheck %s
+//
+// Test generating of TBAA metadata for accesses to members of base classes.
+
+struct A {
+  int x, y, z;
+};
+
+struct B : A {
+  int i;
+};
+
+struct C {
+  int i;
+  B b;
+  int j;
+};
+
+int f1(B *b) {
+// CHECK-LABEL: _Z2f1P1B
+// CHECK: load i32, {{.*}}, !tbaa [[TAG_A_y:!.*]]
+  return b->y;
+}
+
+int f2(C *c) {
+// CHECK-LABEL: _Z2f2P1C
+// CHECK: load i32, {{.*}}, !tbaa [[TAG_A_y]]
+  return (&(c->b))->y;
+}
+
+struct D : virtual A
+{};
+
+struct E {
+  D d;
+};
+
+int f3(D *d) {
+// CHECK-LABEL: _Z2f3P1D
+// CHECK: load i32, {{.*}}, !tbaa [[TAG_A_y]]
+  return d->y;
+}
+
+int f4(E *e) {
+// CHECK-LABEL: _Z2f4P1E
+// CHECK: load i32, {{.*}}, !tbaa [[TAG_A_y]]
+  return (&(e->d))->y;
+}
+
+// CHECK-DAG: [[TYPE_char:!.*]] = !{!"omnipotent char", {{.*}}, i64 0}
+// CHECK-DAG: [[TYPE_int:!.*]] = !{!"int", [[TYPE_char]], i64 0}
+// CHECK-DAG: [[TYPE_A:!.*]] = !{!"_ZTS1A", [[TYPE_int]], i64 0, [[TYPE_int]], i64 4, [[TYPE_int]], i64 8}
+// CHECK-DAG: [[TAG_A_y]] = !{[[TYPE_A]], [[TYPE_int]], i64 4}