[clang][bytecode] Add init link for the RVO ptr (#122904)

Author: tbaederr

clang/lib/AST/ByteCode/Compiler.cpp

@@ -90,6 +90,8 @@ bool InitLink::emit(Compiler<Emitter> *Ctx, const Expr *E) const {
     if (!Ctx->emitConstUint32(Offset, E))
       return false;
     return Ctx->emitArrayElemPtrPopUint32(E);
+  case K_RVO:
+    return Ctx->emitRVOPtr(E);
   case K_InitList:
     return true;
   default:
@@ -4998,6 +5000,7 @@ bool Compiler<Emitter>::visitReturnStmt(const ReturnStmt *RS) {
       if (!this->visit(RE))
         return false;
     } else {
+      InitLinkScope<Emitter> ILS(this, InitLink::RVO());
       // RVO - construct the value in the return location.
       if (!this->emitRVOPtr(RE))
         return false;

clang/lib/AST/ByteCode/Compiler.h

@@ -51,11 +51,13 @@ struct InitLink {
     K_Temp = 2,
     K_Decl = 3,
     K_Elem = 5,
-    K_InitList = 6
+    K_RVO = 6,
+    K_InitList = 7
   };
 
   static InitLink This() { return InitLink{K_This}; }
   static InitLink InitList() { return InitLink{K_InitList}; }
+  static InitLink RVO() { return InitLink{K_RVO}; }
   static InitLink Field(unsigned Offset) {
     InitLink IL{K_Field};
     IL.Offset = Offset;

clang/test/AST/ByteCode/cxx11.cpp

@@ -174,3 +174,14 @@ void lambdas() {
   int d;
   int a9[1] = {[d = 0] = 1}; // both-error {{not an integral constant expression}}
 }
+
+
+namespace InitLinkToRVO {
+  struct A {
+    int y = 3;
+    int z = 1 + y;
+  };
+
+  constexpr A make() { return A {}; }
+  static_assert(make().z == 4, "");
+}