[clang][Interp] Fix initializing array subobjects with This pointers

We need to select the right array element once we see the CXXThisExpr.

Author: tbaederr

clang/lib/AST/Interp/Compiler.cpp

@@ -89,6 +89,10 @@ bool InitLink::emit(Compiler<Emitter> *Ctx, const Expr *E) const {
     return Ctx->emitGetPtrLocal(Offset, E);
   case K_Decl:
     return Ctx->visitDeclRef(D, E);
+  case K_Elem:
+    if (!Ctx->emitConstUint32(Offset, E))
+      return false;
+    return Ctx->emitArrayElemPtrUint32(E);
   default:
     llvm_unreachable("Unhandled InitLink kind");
   }
@@ -1556,6 +1560,7 @@ bool Compiler<Emitter>::visitArrayElemInit(unsigned ElemIndex,
     return this->emitInitElem(*T, ElemIndex, Init);
   }
 
+  InitLinkScope<Emitter> ILS(this, InitLink::Elem(ElemIndex));
   // Advance the pointer currently on the stack to the given
   // dimension.
   if (!this->emitConstUint32(ElemIndex, Init))

clang/lib/AST/Interp/Compiler.h

@@ -50,6 +50,7 @@ struct InitLink {
     K_Field = 1,
     K_Temp = 2,
     K_Decl = 3,
+    K_Elem = 5,
   };
 
   static InitLink This() { return InitLink{K_This}; }
@@ -68,6 +69,11 @@ struct InitLink {
     IL.D = D;
     return IL;
   }
+  static InitLink Elem(unsigned Index) {
+    InitLink IL{K_Elem};
+    IL.Offset = Index;
+    return IL;
+  }
 
   InitLink(uint8_t Kind) : Kind(Kind) {}
   template <class Emitter>

clang/test/AST/Interp/records.cpp

@@ -1537,3 +1537,22 @@ namespace BitSet {
     Bitset()
   };
 }
+
+namespace ArrayInitChain {
+  struct StringLiteral {
+    const char *S;
+  };
+
+  struct CustomOperandVal {
+    StringLiteral Str;
+    unsigned Width;
+    unsigned Mask = Width + 1;
+  };
+
+  constexpr CustomOperandVal A[] = {
+    {},
+  };
+  static_assert(A[0].Str.S == nullptr, "");
+  static_assert(A[0].Width == 0, "");
+  static_assert(A[0].Mask == 1, "");
+}