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patm4
Visitor II
February 13, 2008
Question

RE Cosmic compiler optimisation problems

  • February 13, 2008
  • 6 replies
  • 1439 views
Posted on February 13, 2008 at 05:52

RE Cosmic compiler optimisation problems

    This topic has been closed for replies.

    6 replies

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    patm4Author
    Visitor II
    February 6, 2008
    Posted on February 06, 2008 at 07:52

    I posted on here a while ago about a problem with the Cosmic compiler optimiser V4.5d. I have now tracked this down. Current version is V4.5.5. Changes between V4.5d and V4.4.5 are not relevant, so this bug is still outstanding.

    C code written was :-

    if( wAddr & 0x8000 )

    Code produced with optimisation OFF was :-

    ld a,_ee_GetBlock$L

    bcp a,#128

    jreq L116 ; correct

    Code produced with optimisation ON was :-

    jrpl L116 ; incorrect, test optimised away

    W
    wolfgang2399
    Visitor II
    February 6, 2008
    Posted on February 06, 2008 at 10:50

    Hi,

    jrpl is really the most effective way to test the Most Significant Bit. A good compiler will do it this way.

    In detail:

    Some commands e.g ld a,_ee_GetBlock$L will set the N-flag of the Condition Code Register (CC) when the MSbit is set. Then with jrpl you will jump on condition positiv - means N=0.

    ld a,_ee_GetBlock$L

    jrpl L116

    will meet the condition (only for the MSbit) correctly and is most effective.

    Regards

    WoRo

    L
    luca239955_st
    Visitor II
    February 7, 2008
    Posted on February 07, 2008 at 05:39

    Pat,

    as Woro says, the optimization seems to be correct.

    Why do you think it's a bug? What do you get on your application and what would you expect instead?

    Regards,

    Luca (Cosmic)

    P
    patm4Author
    Visitor II
    February 8, 2008
    Posted on February 08, 2008 at 17:50

    Hi luca

    Thanks for you response.

    I think you have misinterpreted my post.

    The code is optimised down to a single jrpl instruction !

    There is no instruction preceding it to set the flags for the conditional jump.

    Strangely, further along in the code the exact same test is coded correctly.

    L
    luca239955_st
    Visitor II
    February 9, 2008
    Posted on February 09, 2008 at 05:09

    please send me a compilable example reproducing the problem at

    mailto:luca.ubiali@cosmic.fr

    ; I'll provide an explanation or a fix as necessary.

    Regards,

    Luca (Cosmic)

    L
    luca239955_st
    Visitor II
    February 13, 2008
    Posted on February 13, 2008 at 05:52

    just to close this thread, this optimization problem (missing LD before JRPL) was fixed in Jan 2006.

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