Re: [Sdcc-user] missing possible optimizations?

[Bernhard H. <Ber...@be...>]

> So I understand that the mov command given above would not work, since it
> never performs the read on the SFR.  In my case I don't need the read, so
to
> avoid it I'll have to change the way my macro works.  For the general case
> though, wouldn't the following be correct?
>
> mov a,_P_Data                   ; Read the SFR into A
>                                 ; (or any register, if we can't trash A)
> mov _P_Data,_main_response_1_1  ; Directly write the optimized result
Ack.

> To get to this optimization, you would have to go ahead and do constant
> propagation for (P_Data&~P_Data_On_Mask) = 0x00.  Then during dead code
> elimination, we make sure that the read from the SFR is not killed as dead
> code.  I'm guessing this is the current bug you are talking about?  So, I
> think if you make sure the SFR read isn't killed, then the rest of the
> optimizations may already be able to get it to the two lines I gave above.
Yes.

Bernhard