From: Raymond Hettinger <python@rcn.com>
Date: Wed, 7 Nov 2007 02:45:46 +0000 (+0000)
Subject: Add build option for faster loop execution.
X-Git-Tag: v2.6a1~1082
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=dc1d1ba9cfcb8dc1eea9b3960df2b0504ca92727;p=python

Add build option for faster loop execution.
---

diff --git a/Misc/NEWS b/Misc/NEWS
index 997a49a146..b67420b1d0 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -1042,6 +1042,11 @@ Tools/Demos
 Build
 -----
 
+- Add a FAST_LOOPS build option that speeds-up looping by trading away
+  periodic threadstate and signal checking in tight loops.  By default,
+  this option is turned-off.  It should only be enabled in debugged,
+  performance critical applications.
+
 - Patch #786737: Allow building in a tree of symlinks pointing to
   a readonly source.
 
diff --git a/Python/ceval.c b/Python/ceval.c
index 245b08cf23..f86c4fc516 100644
--- a/Python/ceval.c
+++ b/Python/ceval.c
@@ -2159,7 +2159,18 @@ PyEval_EvalFrameEx(PyFrameObject *f, int throwflag)
 		PREDICTED_WITH_ARG(JUMP_ABSOLUTE);
 		case JUMP_ABSOLUTE:
 			JUMPTO(oparg);
+#if FAST_LOOPS
+			/* Enabling this path speeds-up all while and for-loops by bypassing
+                           the per-loop checks for signals.  By default, this should be turned-off
+                           because it prevents detection of a control-break in tight loops like
+                           "while 1: pass".  Compile with this option turned-on when you need
+                           the speed-up and do not need break checking inside tight loops (ones
+                           that contain only instructions ending with goto fast_next_opcode). 
+                        */
+			goto fast_next_opcode;
+#else
 			continue;
+#endif
 
 		case GET_ITER:
 			/* before: [obj]; after [getiter(obj)] */