[lldb] SwiftUserExpression avoid call to ImportType (NFCi)

Currently SwiftASTContext::ImportType was is returning a
TypeSystemSwiftForExpressions TypeRef if the input is a TypeRef
type. This makes future type alias resolution very slow because we
lose the contextual information. By keeping it in the
TypeSystemSwiftTypeRef returned by the Variable these lookups remain
local. This can elminiate up to 90% of the time spent evaluating
expressions in extreme cases.

rdar://145884579
(cherry picked from commit bc64b4e)

Author: adrian-prantl

lldb/source/Plugins/ExpressionParser/Swift/SwiftUserExpression.cpp

@@ -336,7 +336,7 @@ static llvm::Error AddVariableInfo(
       should_not_bind_generic_types &&
       (variable_sp->GetType()->GetForwardCompilerType().GetTypeInfo() &
        lldb::eTypeIsPack);
-
+  bool is_meaningless_without_dynamic_resolution = false;
   // If we're not binding the generic types, we need to set the self type as an
   // opaque pointer type. This is necessary because we don't bind the generic
   // parameters, and we can't have a type with unbound generics in a non-generic
@@ -349,8 +349,13 @@ static llvm::Error AddVariableInfo(
     CompilerType var_type = SwiftExpressionParser::ResolveVariable(
         variable_sp, stack_frame_sp, runtime, use_dynamic, bind_generic_types);
 
-    Status error;
-    target_type = ast_context.ImportType(var_type, error);
+    is_meaningless_without_dynamic_resolution =
+        var_type.IsMeaninglessWithoutDynamicResolution();
+
+    // ImportType would only return a TypeRef type anyway, so it's
+    // faster to leave the type in its original context for faster
+    // type alias resolution.
+    target_type = var_type;
   }
 
   // If the import failed, give up.
@@ -376,8 +381,7 @@ static llvm::Error AddVariableInfo(
   // If we couldn't fully realize the type, then we aren't going
   // to get very far making a local out of it, so discard it here.
   Log *log = GetLog(LLDBLog::Types | LLDBLog::Expressions);
-  if (!is_unbound_pack && ts->IsMeaninglessWithoutDynamicResolution(
-                              target_type.GetOpaqueQualType())) {
+  if (is_meaningless_without_dynamic_resolution) {
     if (log)
       log->Printf("Discarding local %s because we couldn't fully realize it, "
                   "our best attempt was: %s.",