Cache external programs in coredata.

coredata.py

@@ -37,14 +37,9 @@ class CoreData():
         self.strip = options.strip
         self.coverage = options.coverage
 
-        self.deps = {}
-        # To prevent weird bugs, compiler name can not be altered
-        # after it is first declared. So always copy all compilers
-        # from old coredata.
-        if isinstance(options, CoreData):
-            self.compilers = options.compilers.copy()
-        else:
         self.compilers = {}
+        self.deps = {}
+        self.ext_progs = {}
 
 def load(filename):
     obj = pickle.load(open(filename, 'rb'))

interpreter.py

@@ -615,8 +615,12 @@ class Interpreter():
         if not isinstance(required, bool):
             raise InvalidArguments('Line %d: "required" argument must be a boolean.' % node.lineno())
         exename = args[0]
+        if exename in self.coredata.ext_progs and\
+           self.coredata.ext_progs[exename].found():
+            return self.coredata.ext_progs[exename]
         result = shutil.which(exename) # Does .exe appending on Windows.
         progobj = ExternalProgram(exename, result)
+        self.coredata.ext_progs[exename] = progobj
         if required and not progobj.found():
             raise InvalidArguments('Line %d: program "%s" not found.' % (node.lineno(), exename))
         return progobj