Make a small optimization to sre_compile._compile

Switch from expensive old-style-class iteration to our faster iteration.
We could/should probably make old-style iteration much faster than it currently
is for us (10x slower than CPython), but this is a pretty targeted change and
makes compiling regular expressions much faster: it cuts (non-LLVM) _compile()
time by 2x.

from_cpython/Lib/sre_compile.py

@@ -37,7 +37,22 @@ def _compile(code, pattern, flags):
     REPEATING_CODES = _REPEATING_CODES
     SUCCESS_CODES = _SUCCESS_CODES
     ASSERT_CODES = _ASSERT_CODES
-    for op, av in pattern:
+
+    # Pyston change: iterating over a SubPattern is fairly expensive:
+    # - SubPattern defines __getitem__ but not __iter__, so we create a seqiter
+    # - for each iteration, we call instance.getitem, which looks up
+    #   SubPattern.__getitem__, and calls it
+    # - SubPattern.__getitem__ just does `return self.data[idx]`, which throws an
+    #   IndexError to signal that the iteration is done.
+    # All the exceptions and extra layers of indirection add up.
+    # Cut that out by simply iterating over pattern.data, which looks like is
+    # usually a list, and we can use our fast iteration.
+    if isinstance(pattern, sre_parse.SubPattern):
+        pattern_iter = pattern.data
+    else:
+        pattern_iter = pattern
+
+    for op, av in pattern_iter:
         if op in LITERAL_CODES:
             if flags & SRE_FLAG_IGNORECASE:
                 emit(OPCODES[OP_IGNORE[op]])

microbenchmarks/oldstyle_iteration.py

+class C:
+    def __init__(self):
+        self.l = range(10)
+
+    def __getitem__(self, idx):
+        return self.l[idx]
+
+def f():
+    c = C()
+    total = 0
+    for _ in xrange(100000):
+        for i in c:
+            total += i
+    print total
+
+f()
+

src/runtime/stacktrace.cpp

@@ -58,6 +58,9 @@ void raiseRaw(const ExcInfo& e) {
     assert(gc::isValidGCObject(e.traceback));
 
 #if STAT_EXCEPTIONS
+    static StatCounter num_exceptions("num_exceptions");
+    num_exceptions.log();
+
     std::string stat_name;
     if (PyType_Check(e.type))
         stat_name = "num_exceptions_" + std::string(static_cast<BoxedClass*>(e.type)->tp_name);