Fix undeduced type assert

If the instantiation of a member variable makes it possible to
compute a previously undeduced type, we should use that piece of
information.

Fix bug#50590

Differential Revision: https://reviews.llvm.org/D103849

clang/lib/AST/Expr.cpp

@@ -490,6 +490,8 @@ DeclRefExpr *DeclRefExpr::CreateEmpty(const ASTContext &Context,
 
 void DeclRefExpr::setDecl(ValueDecl *NewD) {
   D = NewD;
+  if (getType()->isUndeducedType())
+    setType(NewD->getType());
   setDependence(computeDependence(this, NewD->getASTContext()));
 }
 
@@ -1722,8 +1724,10 @@ MemberExpr *MemberExpr::CreateEmpty(const ASTContext &Context,
   return new (Mem) MemberExpr(EmptyShell());
 }
 
-void MemberExpr::setMemberDecl(ValueDecl *D) {
-  MemberDecl = D;
+void MemberExpr::setMemberDecl(ValueDecl *NewD) {
+  MemberDecl = NewD;
+  if (getType()->isUndeducedType())
+    setType(NewD->getType());
   setDependence(computeDependence(this));
 }
 

clang/test/CodeGenCXX/auto-variable-template.cpp

@@ -12,3 +12,21 @@ int main() { vtemplate<int>(); }
 
 // CHECK: define{{.*}} i32 @main()
 // CHECK: call void @_ZNK1fclEv(%struct.f* {{[^,]*}} @_Z9vtemplateIiE)
+
+template <typename>
+struct pack {
+  template <typename T>
+  constexpr static auto some_boolean_cx_value = true;
+};
+
+auto usage() {
+  return pack<char>::some_boolean_cx_value<int>;
+}
+
+// CHECK: define{{.*}} i1 @_Z5usagev()
+
+auto otherusage() {
+  return pack<char>{}.some_boolean_cx_value<int>;
+}
+
+// CHECK: define{{.*}} i1 @_Z10otherusagev()