Michael Rigby-Jones escreveu:
>   =

>> -----Original Message-----
>> From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On
>>     =

> Behalf
>   =

>> Of Isaac Marino Bavaresco
>> Sent: 26 May 2009 18:34
>> To: Microcontroller discussion list - Public.
>> Subject: RE: [PIC] Source boost V HiTech compilers for C use
>>
>>
>> Look how they do 'Var =3D 0;' :
>>
>> bcf    STATUS,C
>> movlw   0
>> btfsc   STATUS,C
>> movlw   1
>> movwf   Var
>>
>> 'Var =3D 1;'
>>
>> clrf   Var
>> bsf   STATUS,C
>> rlf   Var,f
>>
>> 'Var =3D 2;'
>>
>> clrw
>> iorlw   2
>> movwf   Temp
>> movf   Temp,w
>> movwf   Var
>>
>> And so on... </quote>
>>     =

>
>
> I still don't think it's deliberate, most likely caused by the way the
> new compilers work, with generation of intermediate P code as mentioned
> by someone else.
>   =


What can be less optimized than v =3D n -> movlw n/movwf v? Optimizations
may be: v =3D 0 -> clrf v; v =3D 1 -> clrf v/incf v,f, etc...

> FWIW the older compilers also produced some nonsense code for simple
> expressions prior to optimisation, e.g. from one of my old projects
> using PICC 8.05:
>
>
> 148:               if( TMR1IE && TMR1IF ) {
>   0011    1683     BSF 0x3, 0x5
>   0012    1303     BCF 0x3, 0x6
>   0013    1C0C     BTFSS 0xc, 0
>   0014    281B     GOTO 0x1b
>   0015    2816     GOTO 0x16
>   0016    1283     BCF 0x3, 0x5
>   0017    1C0C     BTFSS 0xc, 0
>   0018    281B     GOTO 0x1b
>   0019    281A     GOTO 0x1a
>   001A    281D     GOTO 0x1d
>   001B    281C     GOTO 0x1c
>   001C    289C     GOTO 0x9c
>   =


Gotos are expected around code inside a if/else construct. When there is
no else and the optimization is off, then you may expect gotos to gotos,
worse if there are ifs inside ifs or elses. What code is inside the if?

This is a completely different type of optimization.

Just analyze the code for 'v =3D 0', in no conceivable way even a crap
compiler may output this code.

> Regards
>
> Mike
>   =



Regards,

Isaac

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