Re: [Qemu-devel] [PATCH 2/7] nios2: Add architecture emulation support

[Richard Henderson]

On 10/18/2016 11:32 AM, Marek Vasut wrote:
> But the instruction encoding does, so I can use the field from the
> instruction to directly index the register array.

Well, no, you can't.

In fact, it would be cleaner to have multiple arrays -- one for general 
registers and one for control registers -- that you *could* actually directly 
index.  There are only two instructions that touch the control registers, rdctl 
and wrctl.  In those instructions you're having to explicitly add 32.

> Thanks, I hope this is fixed now, although I mostly special-case the
> R_ZERO handling throughout the code. Any writes to R_ZERO are now
> ignored and any usage is converted to mov/movi instructions where
> applicable.

We've done that in the past, but in the end it is much cleaner to minimize the 
number of places in which you have to check for R_ZERO.


r~