There’s also LA/LAY which are probably as fast as the XR & SR options.
Keven
On Mon, Aug 10, 2020 at 2:36 PM -0500, "Gary Weinhold" <weinh...@dkl.com> wrote:
I'll make a stab at some principles behind the answer(s): Have the
preceding instructions touched/changed Rn? That could affect the how
long the pipeline may have to idle before changing the register. If the
following instructions will check the condition code or the contents of
the register, they will be delayed. However, the result in Rn can be
predicted before the instruction is executed, so there may be special
circuitry to bypass pipeline steps for these or following instructions.
Are you interested only zeroing the 32-bit RH FW of the 64-bit registers?
On 2020-08-10 3:12 p.m., Schmitt, Michael wrote:
> There are many ways to set a register to binary zero. My question is, which
> is the most efficient?
>
>
> 1. XR Rn,Rn
> 2. SR Rn,RN
> 3. SRA Rn,Rn
> 4. LHI Rn,0
> 5. Other instruction
> 6. Depends on hardware
> 7. Depends on other factors. (What?)
> 8. They are have equal performance
> 9. Method X has worse performance but other advantages. (What?)
>
> ____________________________________
> Michael Schmitt | DXC.technology
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