Memoize environment.Value() to improve performance

The code I work on calls env.Value() often on the same values as part of
consolidating outside dependencies. This change improves performance of that
call by memoizing the results.

2 files changed, 25 insertions, 7 deletions

diff --git a/src/engine/SCons/Environment.py b/src/engine/SCons/Environment.py
index 1296f54..968cc9f 100644
--- a/src/engine/SCons/Environment.py
+++ b/src/engine/SCons/Environment.py
@@ -2220,7 +2220,7 @@ class Base(SubstitutionEnvironment):
     def Value(self, value, built_value=None):
         """
         """
-        return SCons.Node.Python.Value(value, built_value)
+        return SCons.Node.Python.ValueWithMemo(value, built_value)
 
     def VariantDir(self, variant_dir, src_dir, duplicate=1):
         variant_dir = self.arg2nodes(variant_dir, self.fs.Dir)[0]
diff --git a/src/engine/SCons/Node/Python.py b/src/engine/SCons/Node/Python.py
index 4a62f04..f817402 100644
--- a/src/engine/SCons/Node/Python.py
+++ b/src/engine/SCons/Node/Python.py
@@ -31,6 +31,9 @@ __revision__ = "__FILE__ __REVISION__ __DATE__ __DEVELOPER__"
 
 import SCons.Node
 
+_memoLookupMap = {}
+
+
 class ValueNodeInfo(SCons.Node.NodeInfoBase):
     __slots__ = ('csig',)
     current_version_id = 2
@@ -38,18 +41,18 @@ class ValueNodeInfo(SCons.Node.NodeInfoBase):
     field_list = ['csig']
 
     def str_to_node(self, s):
-        return Value(s)
+        return ValueWithMemo(s)
 
     def __getstate__(self):
         """
         Return all fields that shall be pickled. Walk the slots in the class
-        hierarchy and add those to the state dictionary. If a '__dict__' slot is
-        available, copy all entries to the dictionary. Also include the version
-        id, which is fixed for all instances of a class.
+        hierarchy and add those to the state dictionary. If a '__dict__' slot
+        is available, copy all entries to the dictionary. Also include the
+        version id, which is fixed for all instances of a class.
         """
         state = getattr(self, '__dict__', {}).copy()
         for obj in type(self).mro():
-            for name in getattr(obj,'__slots__',()):
+            for name in getattr(obj, '__slots__', ()):
                 if hasattr(self, name):
                     state[name] = getattr(self, name)
 
@@ -76,6 +79,7 @@ class ValueBuildInfo(SCons.Node.BuildInfoBase):
     __slots__ = ()
     current_version_id = 2
 
+
 class Value(SCons.Node.Node):
     """A class for Python variables, typically passed on the command line
     or generated by a script, but not from a file or some other source.
@@ -148,7 +152,6 @@ class Value(SCons.Node.Node):
             # Already encoded as python2 str are bytes
             return text_contents
 
-
     def changed_since_last_build(self, target, prev_ni):
         cur_csig = self.get_csig()
         try:
@@ -173,6 +176,21 @@ class Value(SCons.Node.Node):
         self.get_ninfo().csig = contents
         return contents
 
+
+def ValueWithMemo(value, built_value=None):
+    # No current support for memoizing a value that needs to be built.
+    if built_value:
+        return Value(value, built_value)
+
+    value_str = str(value)
+    if value_str in _memoLookupMap:
+        return _memoLookupMap[value_str]
+
+    v = Value(value)
+    _memoLookupMap[value_str] = v
+    return v
+
+
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