Python: factor out helper predicate to prevent bad join-order.

Author: markshannon

python/ql/src/semmle/python/pointsto/PointsTo.qll

@@ -752,12 +752,6 @@ module PointsTo {
             origin = orig.asCfgNodeOrHere(f)
             |
             mod.getSourceModule() = f.getEnclosingModule() and
-            exists(EssaVariable var |
-                var.getSourceVariable().getName() = name and var.getAUse() = f and
-                ssa_variable_points_to(var, context, value, cls, orig)
-            )
-            or
-            mod.getSourceModule() = f.getEnclosingModule() and
             not exists(EssaVariable var | var.getSourceVariable().getName() = name and var.getAUse() = f) and
             exists(EssaVariable dollar |
                 isModuleStateVariable(dollar) and dollar.getAUse() = f and
@@ -767,6 +761,20 @@ module PointsTo {
             not mod.getSourceModule() = f.getEnclosingModule() and
             Layer::module_attribute_points_to(mod, name, value, cls, orig)
         )
+        or
+        exists(EssaVariable var, CfgOrigin orig |
+            var = ssa_variable_for_module_attribute(f, context) and
+            ssa_variable_points_to(var, context, value, cls, orig) and
+            origin = orig.asCfgNodeOrHere(f)
+        )
+    }
+
+    private EssaVariable ssa_variable_for_module_attribute(ImportMemberNode f, PointsToContext context) {
+        exists(string name, ModuleObject mod, Module m |
+            mod.getSourceModule() = m and m = f.getEnclosingModule() and m = result.getScope() and
+            points_to(f.getModule(name), context, mod, _, _) and
+            result.getSourceVariable().getName() = name and result.getAUse() = f
+        )
     }
 
     /** Holds if `f`  is of the form `getattr(x, "name")` and x.name points to `(value, cls, origin)`. */