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diff --git a/contrib/tools/python3/Lib/lib2to3/btm_matcher.py b/contrib/tools/python3/Lib/lib2to3/btm_matcher.py
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+"""A bottom-up tree matching algorithm implementation meant to speed
+up 2to3's matching process. After the tree patterns are reduced to
+their rarest linear path, a linear Aho-Corasick automaton is
+created. The linear automaton traverses the linear paths from the
+leaves to the root of the AST and returns a set of nodes for further
+matching. This reduces significantly the number of candidate nodes."""
+
+__author__ = "George Boutsioukis <gboutsioukis@gmail.com>"
+
+import logging
+import itertools
+from collections import defaultdict
+
+from . import pytree
+from .btm_utils import reduce_tree
+
+class BMNode(object):
+    """Class for a node of the Aho-Corasick automaton used in matching"""
+    count = itertools.count()
+    def __init__(self):
+        self.transition_table = {}
+        self.fixers = []
+        self.id = next(BMNode.count)
+        self.content = ''
+
+class BottomMatcher(object):
+    """The main matcher class. After instantiating the patterns should
+    be added using the add_fixer method"""
+
+    def __init__(self):
+        self.match = set()
+        self.root = BMNode()
+        self.nodes = [self.root]
+        self.fixers = []
+        self.logger = logging.getLogger("RefactoringTool")
+
+    def add_fixer(self, fixer):
+        """Reduces a fixer's pattern tree to a linear path and adds it
+        to the matcher(a common Aho-Corasick automaton). The fixer is
+        appended on the matching states and called when they are
+        reached"""
+        self.fixers.append(fixer)
+        tree = reduce_tree(fixer.pattern_tree)
+        linear = tree.get_linear_subpattern()
+        match_nodes = self.add(linear, start=self.root)
+        for match_node in match_nodes:
+            match_node.fixers.append(fixer)
+
+    def add(self, pattern, start):
+        "Recursively adds a linear pattern to the AC automaton"
+        #print("adding pattern", pattern, "to", start)
+        if not pattern:
+            #print("empty pattern")
+            return [start]
+        if isinstance(pattern[0], tuple):
+            #alternatives
+            #print("alternatives")
+            match_nodes = []
+            for alternative in pattern[0]:
+                #add all alternatives, and add the rest of the pattern
+                #to each end node
+                end_nodes = self.add(alternative, start=start)
+                for end in end_nodes:
+                    match_nodes.extend(self.add(pattern[1:], end))
+            return match_nodes
+        else:
+            #single token
+            #not last
+            if pattern[0] not in start.transition_table:
+                #transition did not exist, create new
+                next_node = BMNode()
+                start.transition_table[pattern[0]] = next_node
+            else:
+                #transition exists already, follow
+                next_node = start.transition_table[pattern[0]]
+
+            if pattern[1:]:
+                end_nodes = self.add(pattern[1:], start=next_node)
+            else:
+                end_nodes = [next_node]
+            return end_nodes
+
+    def run(self, leaves):
+        """The main interface with the bottom matcher. The tree is
+        traversed from the bottom using the constructed
+        automaton. Nodes are only checked once as the tree is
+        retraversed. When the automaton fails, we give it one more
+        shot(in case the above tree matches as a whole with the
+        rejected leaf), then we break for the next leaf. There is the
+        special case of multiple arguments(see code comments) where we
+        recheck the nodes
+
+        Args:
+           The leaves of the AST tree to be matched
+
+        Returns:
+           A dictionary of node matches with fixers as the keys
+        """
+        current_ac_node = self.root
+        results = defaultdict(list)
+        for leaf in leaves:
+            current_ast_node = leaf
+            while current_ast_node:
+                current_ast_node.was_checked = True
+                for child in current_ast_node.children:
+                    # multiple statements, recheck
+                    if isinstance(child, pytree.Leaf) and child.value == ";":
+                        current_ast_node.was_checked = False
+                        break
+                if current_ast_node.type == 1:
+                    #name
+                    node_token = current_ast_node.value
+                else:
+                    node_token = current_ast_node.type
+
+                if node_token in current_ac_node.transition_table:
+                    #token matches
+                    current_ac_node = current_ac_node.transition_table[node_token]
+                    for fixer in current_ac_node.fixers:
+                        results[fixer].append(current_ast_node)
+                else:
+                    #matching failed, reset automaton
+                    current_ac_node = self.root
+                    if (current_ast_node.parent is not None
+                        and current_ast_node.parent.was_checked):
+                        #the rest of the tree upwards has been checked, next leaf
+                        break
+
+                    #recheck the rejected node once from the root
+                    if node_token in current_ac_node.transition_table:
+                        #token matches
+                        current_ac_node = current_ac_node.transition_table[node_token]
+                        for fixer in current_ac_node.fixers:
+                            results[fixer].append(current_ast_node)
+
+                current_ast_node = current_ast_node.parent
+        return results
+
+    def print_ac(self):
+        "Prints a graphviz diagram of the BM automaton(for debugging)"
+        print("digraph g{")
+        def print_node(node):
+            for subnode_key in node.transition_table.keys():
+                subnode = node.transition_table[subnode_key]
+                print("%d -> %d [label=%s] //%s" %
+                      (node.id, subnode.id, type_repr(subnode_key), str(subnode.fixers)))
+                if subnode_key == 1:
+                    print(subnode.content)
+                print_node(subnode)
+        print_node(self.root)
+        print("}")
+
+# taken from pytree.py for debugging; only used by print_ac
+_type_reprs = {}
+def type_repr(type_num):
+    global _type_reprs
+    if not _type_reprs:
+        from .pygram import python_symbols
+        # printing tokens is possible but not as useful
+        # from .pgen2 import token // token.__dict__.items():
+        for name, val in python_symbols.__dict__.items():
+            if type(val) == int: _type_reprs[val] = name
+    return _type_reprs.setdefault(type_num, type_num)