Performance improvements to counter context.clone slowdown (#1009)

* Add limit to the total number of nodes inferred per context

This change abuses mutable references to create a sort of interior
mutable cell shared between a context and all of its clones. The idea is
that when a node is inferred at the toplevel, it is called with context
= None, creating a new InferenceContext and starting a count from zero.
However, when a context is cloned we re-use the cell and cause the count
in the "parent" context to be incremented when nodes are inferred in the
"child" context.

* Add global inference cache
* Update safe_infer to catch StopIteration

5 files changed, 64 insertions, 15 deletions

diff --git a/ChangeLog b/ChangeLog
index 1286a980..019dbb91 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -16,6 +16,11 @@ Release Date: TBA
 
 * Add lineno and col_offset for ``Keyword`` nodes and Python 3.9+
 
+* Add global inference cache to speed up inference of long statement blocks
+
+* Add a limit to the total number of nodes inferred indirectly as a result
+  of inferring some node
+
 
 What's New in astroid 2.5.7?
 ============================
diff --git a/astroid/context.py b/astroid/context.py
index 440d1ceb..08985841 100644
--- a/astroid/context.py
+++ b/astroid/context.py
@@ -13,7 +13,17 @@
 """Various context related utilities, including inference and call contexts."""
 import contextlib
 import pprint
-from typing import Optional
+from typing import TYPE_CHECKING, MutableMapping, Optional, Sequence, Tuple
+
+if TYPE_CHECKING:
+    from astroid.node_classes import NodeNG
+
+
+_INFERENCE_CACHE = {}
+
+
+def _invalidate_cache():
+    _INFERENCE_CACHE.clear()
 
 
 class InferenceContext:
@@ -28,11 +38,17 @@ class InferenceContext:
         "lookupname",
         "callcontext",
         "boundnode",
-        "inferred",
         "extra_context",
+        "_nodes_inferred",
     )
 
-    def __init__(self, path=None, inferred=None):
+    max_inferred = 100
+
+    def __init__(self, path=None, nodes_inferred=None):
+        if nodes_inferred is None:
+            self._nodes_inferred = [0]
+        else:
+            self._nodes_inferred = nodes_inferred
         self.path = path or set()
         """
         :type: set(tuple(NodeNG, optional(str)))
@@ -65,14 +81,6 @@ class InferenceContext:
 
         e.g. the bound node of object.__new__(cls) is the object node
         """
-        self.inferred = inferred or {}
-        """
-        :type: dict(seq, seq)
-
-        Inferred node contexts to their mapped results
-        Currently the key is ``(node, lookupname, callcontext, boundnode)``
-        and the value is tuple of the inferred results
-        """
         self.extra_context = {}
         """
         :type: dict(NodeNG, Context)
@@ -81,6 +89,34 @@ class InferenceContext:
         for call arguments
         """
 
+    @property
+    def nodes_inferred(self):
+        """
+        Number of nodes inferred in this context and all its clones/decendents
+
+        Wrap inner value in a mutable cell to allow for mutating a class
+        variable in the presence of __slots__
+        """
+        return self._nodes_inferred[0]
+
+    @nodes_inferred.setter
+    def nodes_inferred(self, value):
+        self._nodes_inferred[0] = value
+
+    @property
+    def inferred(
+        self,
+    ) -> MutableMapping[
+        Tuple["NodeNG", Optional[str], Optional[str], Optional[str]], Sequence["NodeNG"]
+    ]:
+        """
+        Inferred node contexts to their mapped results
+
+        Currently the key is ``(node, lookupname, callcontext, boundnode)``
+        and the value is tuple of the inferred results
+        """
+        return _INFERENCE_CACHE
+
     def push(self, node):
         """Push node into inference path
 
@@ -103,7 +139,7 @@ class InferenceContext:
         starts with the same context but diverge as each side is inferred
         so the InferenceContext will need be cloned"""
         # XXX copy lookupname/callcontext ?
-        clone = InferenceContext(self.path.copy(), inferred=self.inferred.copy())
+        clone = InferenceContext(self.path.copy(), nodes_inferred=self._nodes_inferred)
         clone.callcontext = self.callcontext
         clone.boundnode = self.boundnode
         clone.extra_context = self.extra_context
diff --git a/astroid/helpers.py b/astroid/helpers.py
index cb16ecdc..db86606e 100644
--- a/astroid/helpers.py
+++ b/astroid/helpers.py
@@ -150,7 +150,7 @@ def safe_infer(node, context=None):
     try:
         inferit = node.infer(context=context)
         value = next(inferit)
-    except exceptions.InferenceError:
+    except (exceptions.InferenceError, StopIteration):
         return None
     try:
         next(inferit)
diff --git a/astroid/node_classes.py b/astroid/node_classes.py
index ff74fa21..85e3cea6 100644
--- a/astroid/node_classes.py
+++ b/astroid/node_classes.py
@@ -357,12 +357,16 @@ class NodeNG:
             # explicit_inference is not bound, give it self explicitly
             try:
                 # pylint: disable=not-callable
-                yield from self._explicit_inference(self, context, **kwargs)
+                results = tuple(self._explicit_inference(self, context, **kwargs))
+                if context is not None:
+                    context.nodes_inferred += len(results)
+                yield from results
                 return
             except exceptions.UseInferenceDefault:
                 pass
 
         if not context:
+            # nodes_inferred?
             yield from self._infer(context, **kwargs)
             return
 
@@ -378,11 +382,12 @@ class NodeNG:
         # exponentially exploding possible results.
         limit = MANAGER.max_inferable_values
         for i, result in enumerate(generator):
-            if i >= limit:
+            if i >= limit or (context.nodes_inferred > context.max_inferred):
                 yield util.Uninferable
                 break
             results.append(result)
             yield result
+            context.nodes_inferred += 1
 
         # Cache generated results for subsequent inferences of the
         # same node using the same context
diff --git a/astroid/transforms.py b/astroid/transforms.py
index 1c4081cb..5314fcb2 100644
--- a/astroid/transforms.py
+++ b/astroid/transforms.py
@@ -10,6 +10,8 @@
 import collections
 from functools import lru_cache
 
+from astroid import context as contextmod
+
 
 class TransformVisitor:
     """A visitor for handling transforms.
@@ -42,6 +44,7 @@ class TransformVisitor:
                 # if the transformation function returns something, it's
                 # expected to be a replacement for the node
                 if ret is not None:
+                    contextmod._invalidate_cache()
                     node = ret
                 if ret.__class__ != cls:
                     # Can no longer apply the rest of the transforms.