Re: [PATCH 0/9] Collapse CPUNegativeOffsetState into CPUState

[Anton Johansson]

On 7/1/23 11:21, Paolo Bonzini wrote:
> On 6/30/23 14:25, Anton Johansson via wrote:
> > CPUNegativeOffsetState is a struct placed immediately before
> > CPUArchState in the ArchCPU struct.  Its purpose is to ensure that
> > certain fields (CPUTLBDescFast, IcountDecr) lay within a small negative
> > offset of CPUArchState in memory.  This is desired for better
> > code-generation on arm[32|64] and riscv hosts which has addressing
> > modes with 12- and 11 bits of displacement respectively.
>
> The purpose is also to ensure that general purpose registers stay 
> close to the beginning of the CPUArchState and thus can also be 
> accessed with a small displacement.
>
> Can you check if this becomes worse for any architecture?  On some 
> 64-bit targets, 8 bytes * 32 registers is 512 bytes and it's a 
> substantial part of the 11 bits that are available.
>
> Paolo
I'm dropping the CPUNegativeOffsetState changes, but the fields would 
still have had
a negative displacement from the beginning of env, so the positive 
offset of the gprs from env
wouldn't be affected.

--
Anton Johansson,
rev.ng Labs Srl.