On Aug 10, 2012, at 4:13 PM, Dave McGuire wrote: On 08/10/2012 04:07 PM, Paul_Koning at Dell.com wrote: Yes, the makefile sets the optimize flags. It tells it to optimize pretty hard, but I'm redoing some tests with a later version. I'm also going to try (first time I've done that) profile directed optimizing. The simh code at one point used inline, but not any longer. It may be relying on recent compilers to do that automaticallly, I'll find out. What target architecture are you compiling for? x86_64-linux. And x86_64-darwin. GCC is known to produce very good code for x86_64. I think it might be worth giving LLVM a try, but I don't think you'll get quite the output quality of GCC. Try adding -fomit-frame-pointer; that will free up a register, which is pretty important on register-starved architectures such as x86 and x86_64. (depending on your -O<n> level, it might already be turned on though) According to the manpage, that's already the default as of GCC V4.6. I'm currently doing some tests with GCC 4.7.0, the latest release. paul