In the example above, it's not only register allocation, but also scheduling. The data needs to be loaded from memory, and how that happens can affect performance quite a bit. And yeah, I can't understand how 8.1 could get decent performance without instruction scheduling... but maybe I'm stuck in my own little RISC processing world (the (toy) compilers I have written have been for SPARC and MIPS), and I just don't understand enough about how the pentium works. Brian On Fri, 25 Feb 2005 14:24:27 -0500, Daniel Berlin <dberlin@xxxxxxxxxxx> wrote: > On Fri, 2005-02-25 at 12:18 +0100, Brian Budge wrote: > > Hmmm, I doubt that. It seems very important that your data be in > > registers when you want to do arithmetic on it. > > That's register allocation, not scheduling :) > > > > > I can see that if your data was already in registers, maybe a > > "randomized" instruction ordering would perform okay, but loading the > > data properly is time consuming. At least these are the things I've > > observed. > > > > stevenb was the source of this information for me, so maybe he can > confirm it (Steven, i mentioned to brian that icc 8.1 doesn't do > scheduling for the pentium4 anymore, and he doubts it :P) > >
