Re: [Qemu-devel] qemu vs gcc4

[Rob Landley]

On Tuesday 31 October 2006 2:02 pm, Paul Brook wrote:

> As an example take the arm instruction
> 
>   add, r0, r1, r2, lsl #2
> 
> This is equivalent to the C expression
> 
>  r0 = r1 + (r2 << 2)
...
> When fully converted to the new system this would become:
> 
>   int tmp = gen_new_qreg(); /* Allocate a temporary reg.  */
>   /* gen_im32 is a helper that allocates a new qreg and
>      initializes it to an immediate value.  */
>   gen_op_add32(tmp, QREG_R2, gen_im32(2));
>   gen_op_add32(QREG_R0, QREG_R1, tmp);

I forgot to ask:

Where's the shift?  I think the above code means you generate an immediate 
value (the 2), add it to R2 with the result going in a spill register, and 
then add the spill register to R1, with the result going to R0.  Should that 
middle line be some kind of gen_op_lshift32() instead of gen_op_add32()?

Do qregs ever get freed?  (I'm guessing gen_new_qreg() lasts until the end of 
the translated block, and then the next block has its own set of qregs?)

Rob
-- 
"Perfection is reached, not when there is no longer anything to add, but
when there is no longer anything to take away." - Antoine de Saint-Exupery