Re: [Qemu-devel] [PATCH v4 01/15] target-tricore: Add target stubs and qom-cpu

[Bastian Koppelmann]

On 08/08/2014 03:28 AM, Richard Henderson wrote:
> On 08/07/2014 04:34 AM, Bastian Koppelmann wrote:
> > +    /* PSW flag cache for faster execution
> > +       if flag != 0 then flag is set. Else flag is not set.
> > +    */
> > +    target_ulong PSW_USB_C;
> > +    target_ulong PSW_USB_V;
> > +    target_ulong PSW_USB_SV;
> > +    target_ulong PSW_USB_AV;  /* Only if bit 31 set, then flag is set. */
> > +    target_ulong PSW_USB_SAV; /* Only if bit 31 set, then flag is set. */
> V and SV are also only set if bit 31 is set, the way we're computing overflow
> from addition.  Of course, overflow from saturation or multiplication isn't
> being computed into bit 31, so there is a decision to make.
>
> Depending on how important it is for ADDX+ADDC to be implemented efficiently,
> vs how important is for SHA to be quick, you may wish to have C already set to
> 0/1 only.

Since I don't have data, which instructions are more common, I would 
choose the SHA instructions to be fast, because the manual states, that 
the most commen instructions are also implemented as 16 bit instructions 
and SHA is part of those. So I would leave the carry bit as is, unless 
you are sure, that there is a benefit for ADDX+ADDC to be fast.

> r~