It's important to keep the concepts of 64-bit registers separate from 64-bit addressing. The former supports that latter, but there are many capabilities and benefits of 64-bit registers that have nothing to do with addressing. Most -G instructions work the same in any addressing mode. A few instructions (LA & cousins in particular) are modal, and do operate differently depending on AMODE.
Chapter 1 of of Principles of Operation, particularly the "Trimodal Addressing" section, covers this fairly well. sas On Tue, May 5, 2015 at 9:36 AM, Brite < [email protected]> wrote: > I compared to the performance of same programs before they were converted > to 64-bit. How do those 64-bit instructions (e.g. LGR, STMG, LMG) work in > 31-bit AMODE? This is the first I have to deal with 64-bit mode. > -- sas
