Re: [PATCH 1/2] target/i386: fix cmpxchg with 32-bit register destination

[Paolo Bonzini]

On 9/12/22 09:55, Richard Henderson wrote:
>   * Compute...
>
> Why bother passing NULL, and fixing it up at each use...
>
> > +static void gen_op_mov_reg_v(DisasContext *s, MemOp ot, int reg, TCGv 
> > t0)
> > +{
> > +    gen_op_deposit_reg_v(s, ot, reg, NULL, t0);
> >   }
>
> ... when you can just as easily pass in the register here?

Because dest can be fixed up to either cpu_regs[reg - 4] for high-byte 
registers, or cpu_regs[reg] for everything else.

> We have an outstanding bug report that suggests that the move to eax must use 
> the deposit in both cases:
>
> https://gitlab.com/qemu-project/qemu/-/issues/508

Ok, so that's two bugs.  But both of them can indeed be fixed with 
gen_op_deposit_reg_v.

Paolo