[clang][bytecode] Add InitLinkScope for toplevel Expr temporary (#123319)

Author: tbaederr

clang/lib/AST/ByteCode/Compiler.cpp

@@ -4247,6 +4247,7 @@ bool Compiler<Emitter>::visitExpr(const Expr *E, bool DestroyToplevelScope) {
   // For us, that means everything we don't
   // have a PrimType for.
   if (std::optional<unsigned> LocalOffset = this->allocateLocal(E)) {
+    InitLinkScope<Emitter> ILS(this, InitLink::Temp(*LocalOffset));
     if (!this->emitGetPtrLocal(*LocalOffset, E))
       return false;
 

clang/test/AST/ByteCode/cxx20.cpp

@@ -893,3 +893,18 @@ namespace VirtDtor {
 
   static_assert(test('C', 'B'));
 }
+
+namespace TemporaryInNTTP {
+  template<auto n> struct B { /* ... */ };
+  struct J1 {
+    J1 *self=this;
+  };
+  /// FIXME: The bytecode interpreter emits a different diagnostic here.
+  /// The current interpreter creates a fake MaterializeTemporaryExpr (see EvaluateAsConstantExpr)
+  /// which is later used as the LValueBase of the created APValue.
+  B<J1{}> j1;  // ref-error {{pointer to temporary object is not allowed in a template argument}} \
+               // expected-error {{non-type template argument is not a constant expression}} \
+               // expected-note {{pointer to temporary is not a constant expression}} \
+               // expected-note {{created here}}
+  B<2> j2; /// Ok.
+}