William "Chops" Westfield escreveu:
>>> WTF is going on with the Hi-Tech compiler that ships with MPLAB....
>>>       =

>
> It used to be that one was taught to have their compiler output  =

> "standard format intermediate code" (usually triple operand things  =

> that matched no real machines at all:  "operation source1, source2 =3D=3D=
>  =

> destination".)   Then, "later", one would write a code generator that  =

> would optimize that in ways specific to a destination CPU.  (actually,  =

> I guess you get at least three chances to optimize; you can optimized  =

> the intermediate code, optimize the generation of real code, and then  =

> optimize the resulting machine code.)
>
> The Hi-tech compiler *is* (was?) multi-target, so it probably has some  =

> sort of common back-end and does something very like this sort of code  =

> generation.
>
>
> I wasn't impressed, back when I was taught this. :-(
>
> I'm not impressed now, when it sort-of looks like Hi-tech has  =

> implemented their free compiler by replacing the code generator with  =

> something that is at best trivial and perhaps intentionally bad...
>
>   =

>> 365:               irrxsum1+=3Dirbyte1;
>>   115    087A     MOVF 0x7a, W
>>   116    00C3     MOVWF 0x43
>>   117    0843     MOVF 0x43, W
>>   118    07F4     ADDWF 0x74, F
>>
>> Should be 2 instructions
>>     =

>
> This matches up well with "add irrxsum1, irbyte1 =3D=3D> irrxsum1 ?
>
> Also don't forget that C expressions like the source code here are  =

> defined to "return" a value, so it's not beyond reasonableness that  =

> completely unoptimized code would want to leave the value of each  =

> expression calculation in W.
>
>   =

>> 366:               ircnt1=3D0;
>>   119    1003     BCF 0x3, 0
>>   11A    3000     MOVLW 0
>>   11B    1803     BTFSC 0x3, 0
>>   11C    3001     MOVLW 0x1
>>   11D    00FB     MOVWF 0x7b
>>
>> This is especially bizarre - should be 1 CLRF instruction
>>     =

>
> Yeah.  Perhaps the compiler has special code to handle common small  =

> constants like zero and one, but without optimization the test stays  =

> in the code?
>
> I think this was a really bad move on hi-tech's part.  It makes them  =

> look bad, it makes compilers in general look bad.  I applaud (sort of)  =

> the attempt at a new way of handling "free" versions of commercial  =

> compilers, but I really hope that Microsoft decides that this is a  =

> failed experiment and does something else in the future.
>
> BillW

OK, explain this under this theory:

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

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