On 2 June 2014 19:56, Robin Vowels <[email protected]> wrote: > From: "Tony Harminc" <[email protected]> > Sent: Tuesday, June 03, 2014 3:30 AM
>> Is LHI Rn,0 faster than SR Rn,Rn? I'd expect them to be the same, but >> SR is half the size, and so lessens the amount of i-cache used. > > XR Rn,Rn is faster than SR. I doubt it. Perhaps on much older machines, but I have little doubt that modern machines have special cases for most or all common ways of zeroing a register, e.g. SR Rn, Rn and XR Rn, Rn and LA Rn,0 and LHI Rn,0 . And of course these are just the 32-bit versions. Yes, of course there are many more ways of zeroing a register, but I doubt there's much of a business case for optimizing things like LAY for this. > But does it matter? > Such an instruction should be executed only once, and once only. > It shouldn't be in the loop. Well that surely depends on what the loop is doing. Tony H.
