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Another optimizer bug (*solved*) - Printable Version

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Another optimizer bug (*solved*) - einar - 11-04-2014

Ouch! This bug gave me a headache! It took me some time to figure out the reason my game was crashing...

Take a look at this sample:

Code:
sub test()
    asm
        call    $fc12
        di
        ld      a, $fe
        ld      i, a
        im      2
        ei
    end asm
end sub

test()

Try compiling this sample above using:

Code:
zxb.exe -A -O2 prog.bas

And it will produce the expected result:

Code:
_test:
    push ix
    ld ix, 0
    add ix, sp
#line 1
        call    $fc12
        di
        ld      a, $fe
        ld      i, a
        im      2
        ei
#line 7
_test__leave:
    ld sp, ix
    pop ix
    ret

However try compiling it again using:

Code:
zxb.exe -A -O3 prog.bas

Now the result won't make sense anymore:

Code:
_test:
    push ix
    ld ix, 0
    add ix, sp
#line 1
    call    $fc12
    di
    im      2
    ei
#line 7
_test__leave:
    ld sp, ix
    pop ix
    ret

The problem is, the optimizer is supposed to try to optimize its own generated code only, not someone else's assembly code that it doesn't have enough information to understand!

Re: Another optimizer bug - boriel - 12-27-2014

Try and download the new version ZX BASIC 1.4.0s1902.

It's true the compiler should not optimize user's asm code. But at the moment it's not implemented.
However, the bug was it was not taking into account neither the I register nor the IM instruction. So it was a bug anyway. Wink
Now your example works ok for me.

Can you try it, please??

Re: Another optimizer bug - einar - 12-27-2014

It works, thanks a lot!

Re: Another optimizer bug - boriel - 12-27-2014

einar Wrote:It works, thanks a lot!
You're welcome! Smile
A trick to avoid the compiler to optimize your code is to encode the asm using DEFB, DEFW (the bytes) but it's a so hard task... :roll: