clean up and improve static type declarations in FlowControl.py a bit

Cython/Compiler/FlowControl.pxd

 cimport cython
 
+from Cython.Compiler.Visitor cimport CythonTransform, TreeVisitor
+
 cdef class ControlBlock:
      cdef public set children
      cdef public set parents
@@ -39,6 +41,9 @@ cdef class AssignmentList:
     cdef public object mask
     cdef public list stats
 
+cdef class AssignmentCollector(TreeVisitor):
+    cdef list assignments
+
 cdef class ControlFlow:
      cdef public set blocks
      cdef public set entries
@@ -51,9 +56,10 @@ cdef class ControlFlow:
 
      cdef public dict assmts
 
-     cpdef newblock(self, parent=*)
-     cpdef nextblock(self, parent=*)
+     cpdef newblock(self, ControlBlock parent=*)
+     cpdef nextblock(self, ControlBlock parent=*)
      cpdef bint is_tracked(self, entry)
+     cpdef bint is_statically_assigned(self, entry)
      cpdef mark_position(self, node)
      cpdef mark_assignment(self, lhs, rhs, entry)
      cpdef mark_argument(self, lhs, rhs, entry)
@@ -74,5 +80,20 @@ cdef class ControlFlow:
 cdef class Uninitialized:
      pass
 
+cdef class Unknown:
+    pass
+
 @cython.locals(dirty=bint, block=ControlBlock, parent=ControlBlock)
 cdef check_definitions(ControlFlow flow, dict compiler_directives)
+
+cdef class ControlFlowAnalysis(CythonTransform):
+    cdef object gv_ctx
+    cdef set reductions
+    cdef list env_stack
+    cdef list stack
+    cdef object env
+    cdef ControlFlow flow
+    cdef bint in_inplace_assignment
+
+    cpdef mark_assignment(self, lhs, rhs=*)
+    cpdef mark_position(self, node)