search for: register_renam

...LU to execute "mov", > then mov - add must have dependency. I think you will find it is more complicated than that. A 'mov' usually doesn't need an ALU resource. You should read about the 'reservation station' style register renaming. http://en.wikipedia.org/wiki/Register_renaming http://www.intel.com/Assets/PDF/manual/248966.pdf /jakob

>>                 8B C3 mov eax, ebx >>                 03 C1 add eax, ecx >> becomes >>                 8B C3 03 C1 add eax, ebx, ecx In my understanding, twoaddr pass tends to emit such a sequence. Though I don't have sandybridge, I have not measured. Prior processors(intel and amd) might spend 1 ALU to execute "mov", then mov - add must have dependency.

...gt; then mov - add must have dependency. > > I think you will find it is more complicated than that. A 'mov' usually > doesn't need an ALU resource. > > You should read about the 'reservation station' style register renaming. > > http://en.wikipedia.org/wiki/Register_renaming > http://www.intel.com/Assets/PDF/manual/248966.pdf > > /jakob > > -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20110417/8f1cd34f/attachment.html>

On Apr 8, 2011, at 3:29 AM, Nicolas Capens wrote: > x86 processors use macro-op fusion to merge together two instructions and execute them as one. So it's beneficial for the compiler to emit them as a pair. > > Currently only compare and jump instructions get fused though. And I was wondering whether it also makes sense to fuse move and arithmetic instructions together, to form