gdb/varobj: Only re-evaluate invalid globals during re_set

When doing varobj_re_set, we currently try to recreate floating varobj.
This was introduced by 4e969b4 "Re-evaluate floating varobj as part
of varobj_invalidate" to deal with use a after free issue.  However
since bc20e56 "Fix use after free in varobj" we now ensure that we
never have dangling pointers so this all recreation is not strictly
needed anymore for floating varobjs.

This commit proposes to remove this recreation process for floating
varobjs.

Tested on x86_64-linux.

gdb/testsuite/gdb.mi/mi-var-invalidate.exp

@@ -75,8 +75,8 @@ mi_runto_main
 # Change format of floating variable immediately after reload reveals a
 # bug where gdb still uses a free'd pointer.
 mi_gdb_test "-var-set-format float_simple hexadecimal" \
-        "\\^done,format=\"hexadecimal\",value=\"\\\[-1\\\]\"" \
-       "set format variable float_simple"
+	"\\^done,format=\"hexadecimal\",value=\"\\\[3\\\]\"" \
+	"set format variable float_simple"
 
 # Check local variable is "invalid".
 mi_gdb_test "-var-update linteger" \

gdb/varobj.c

@@ -2359,29 +2359,21 @@ all_root_varobjs (gdb::function_view<void (struct varobj *var)> func)
 static void
 varobj_re_set_iter (struct varobj *var)
 {
-  /* Invalidated globals and floating var must be re-evaluated.  */
-  if (var->root->global || var->root->floating)
+  /* Invalidated global varobjs must be re-evaluated.  */
+  if (!var->root->is_valid && var->root->global)
     {
       struct varobj *tmp_var;
 
       /* Try to create a varobj with same expression.  If we succeed
-	 replace the old varobj, otherwise invalidate it.  */
+	 and have a global replace the old varobj.  */
       tmp_var = varobj_create (nullptr, var->name.c_str (), (CORE_ADDR) 0,
-			       var->root->floating
-			       ? USE_SELECTED_FRAME : USE_CURRENT_FRAME);
-      if (tmp_var != nullptr)
+			       USE_CURRENT_FRAME);
+      if (tmp_var != nullptr && tmp_var->root->global)
 	{
-	  gdb_assert (var->root->floating == tmp_var->root->floating);
 	  tmp_var->obj_name = var->obj_name;
 	  varobj_delete (var, 0);
 	  install_variable (tmp_var);
 	}
-      else if (var->root->global)
-	{
-	  /* Only invalidate globals as floating vars might still be valid in
-	     some other frame.  */
-	  var->root->is_valid = false;
-	}
     }
 }