From 23f1b5ff66d94400ed629487d0893946cdf0a175 Mon Sep 17 00:00:00 2001 From: Paul Sokolovsky Date: Sun, 28 Dec 2014 07:44:09 +0200 Subject: [PATCH] py: Add note about -fno-crossjumping when compiling vm.c. --- py/py.mk | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/py/py.mk b/py/py.mk index 99fc0223ce..f54c06cbcf 100644 --- a/py/py.mk +++ b/py/py.mk @@ -162,3 +162,11 @@ $(PY_BUILD)/gc.o: CFLAGS += $(CSUPEROPT) # optimising vm for speed, adds only a small amount to code size but makes a huge difference to speed (20% faster) $(PY_BUILD)/vm.o: CFLAGS += $(CSUPEROPT) +# Optimizing vm.o for modern deeply pipelined CPUs with branch predictors +# may require disabling tail jump optimization. This will make sure that +# each opcode has its own dispatching jump which will improve branch +# branch predictor efficiency. +# http://article.gmane.org/gmane.comp.lang.lua.general/75426 +# http://hg.python.org/cpython/file/b127046831e2/Python/ceval.c#l828 +# http://www.emulators.com/docs/nx25_nostradamus.htm +#-fno-crossjumping