Issue #4753: By enabling a configure option named '--with-computed-gotos'

on compilers that support it (notably: gcc, SunPro, icc), the bytecode
evaluation loop is compiled with a new dispatch mechanism which gives
speedups of up to 20%, depending on the system, on various benchmarks.

Python/makeopcodetargets.py

@@ -0,0 +1,43 @@
+#! /usr/bin/env python
+"""Generate C code for the jump table of the threaded code interpreter
+(for compilers supporting computed gotos or "labels-as-values", such as gcc).
+"""
+
+import imp
+import os
+
+
+def find_module(modname):
+    """Finds and returns a module in the local dist/checkout.
+    """
+    modpath = os.path.join(
+        os.path.dirname(os.path.dirname(__file__)), "Lib")
+    return imp.load_module(modname, *imp.find_module(modname, [modpath]))
+
+def write_contents(f):
+    """Write C code contents to the target file object.
+    """
+    opcode = find_module("opcode")
+    targets = ['_unknown_opcode'] * 256
+    for opname, op in opcode.opmap.items():
+        if opname == "STOP_CODE":
+            # XXX opcode not implemented
+            continue
+        targets[op] = "TARGET_%s" % opname
+    f.write("static void *opcode_targets[256] = {\n")
+    f.write(",\n".join("\t&&%s" % s for s in targets))
+    f.write("\n};\n")
+
+
+if __name__ == "__main__":
+    import sys
+    assert len(sys.argv) < 3, "Too many arguments"
+    if len(sys.argv) == 2:
+        target = sys.argv[1]
+    else:
+        target = "Python/opcode_targets.h"
+    f = open(target, "w")
+    try:
+        write_contents(f)
+    finally:
+        f.close()