On 1/21/2014 5:24 PM, Jim Mulder wrote:
From a hardware design engineer: <quote> All hardware instructions perform at the same speed in 64-bit mode or 31-bit mode. I assume the AMODE(31) and AMODE(64) he is referring to only affects the addressing mode, but the exact same instruction sequences are used in both cases. If different code sequences are being used, then all bets are off. My first statement applies to the exact same code sequence in 64-bit addressing mode versus 31-bit addressing mode. A few millicoded instructions do have slightly different path lengths depending on addressing mode, but even that is not common. <endquote>
Perhaps JG's assertion is actually about "grande" instructions vs "normal" instructions. Our benchmarks show grande instructions are ever-so-slightly (<2%) slower than their non-grande counterparts. Example: L vs LG.
Of course, the instruction path for the six-byte grande "LG" benchmark code is 50% larger (in terms of space occupied, not instructions issued) than its four-byte non-grande "L" counterpart, meaning more i-cache is required to run it. So, perhaps that is to what this <2% difference is attributable.
Either way, it's something we consistently observe... -- Edward E Jaffe Phoenix Software International, Inc 831 Parkview Drive North El Segundo, CA 90245 http://www.phoenixsoftware.com/ ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN
