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undesirable 'optimization'

erik malund

the source (shown from the list):

 312   3            /* shift out the column data */
 313   3            for (index = 0; index < 8; index++)
 314   3            { // column clock to 0, clear column data pin
 315   4              SB_P1_FDDA_N = 1;
 316   4              if (CPBCsdat & 0x80) SB_P1_FDDA_N = 0;
 317   4              CPBCsdat <<= 1;
 318   4              delay();
 319   4              SB_P1_FDCK_N = 1;
 320   4              delay();
 321   4              SB_P1_FDCK_N = 0;
 322   4            } /* end for index */
generates the assembly:
                                           ; ; SOURCE LINE # 313
;---- Variable 'index' assigned to Register 'R3' ----
000C E4                CLR     A
000D FB                MOV     R3,A
000E         ?C0025:
                                           ; SOURCE LINE # 314
                                           ; SOURCE LINE # 315
000E D290              SETB    SB_P1_FDDA_N
                                           ; SOURCE LINE # 316
0010 EC                MOV     A,R4
0011 30E702            JNB     ACC.7,?C0028
0014 C290              CLR     SB_P1_FDDA_N
0016         ?C0028:
                                           ; SOURCE LINE # 317
                                           ; SOURCE LINE # 318
                                           ; SOURCE LINE # 319
                                           ; SOURCE LINE # 320
0016 120000      R     LCALL   ?C0086
                                           ; SOURCE LINE # 321
0019 C291              CLR     SB_P1_FDCK_N
                                           ; SOURCE LINE # 322
001B 0B                INC     R3
001C BB08EF            CJNE    R3,#08H,?C0025
what happened to lines 318 and 319?

Erik

Parents
  • 0 in reply to erik malund

    I took your example and extended it a bit as it didn't optimise at all as given:

    bit a;

    void hello(void)
    {
    volatile char b=1;

    b++;
    }

    main()
    {

    a=1;
    hello();

    a=0;
    hello();

    a=1;
    hello();

    a=0;
    hello();

    a=1;
    hello();

    a=0;
    hello();

    a=1;
    hello();

    while(1);
    }

    At optimisation level 0 my .cod file was as follows:

    ----- FUNCTION hello (BEGIN) -----
    FILE: 'junk.c'
    32: void hello(void)
    33: {
    34: volatile char b=1;
    35:
    00000F 750801 MOV b,#01H
    36: b++;
    000012 0508 INC b
    37: }
    000014 22 RET
    ----- FUNCTION hello (END) -------


    ----- FUNCTION main (BEGIN) -----
    FILE: 'junk.c'
    39: main()
    40: {
    41:
    42: a=1;
    000015 D200 SETB a
    43: hello();
    000017 110F ACALL hello
    44:
    45: a=0;
    000019 C200 CLR a
    46: hello();
    00001B 110F ACALL hello
    47:
    48: a=1;
    00001D D200 SETB a
    49: hello();
    00001F 110F ACALL hello
    50:
    51: a=0;
    000021 C200 CLR a
    52: hello();
    000023 110F ACALL hello
    53:
    54: a=1;
    000025 D200 SETB a
    55: hello();
    000027 110F ACALL hello
    56:
    57: a=0;
    000029 C200 CLR a
    58: hello();
    00002B 110F ACALL hello
    59:
    60: a=1;
    00002D D200 SETB a
    61: hello();
    00002F 110F ACALL hello
    000031 ?C0002?JUNK:
    62:
    63: while(1);
    000031 80FE SJMP ?C0002?JUNK
    64: }
    000033 22 RET
    ----- FUNCTION main (END) -------

    which doesn't show any optimisation at all.

    I think you must really be compiling with a higher level of optimisation than zero.

    Stefan

Reply
  • 0 in reply to erik malund

    I took your example and extended it a bit as it didn't optimise at all as given:

    bit a;

    void hello(void)
    {
    volatile char b=1;

    b++;
    }

    main()
    {

    a=1;
    hello();

    a=0;
    hello();

    a=1;
    hello();

    a=0;
    hello();

    a=1;
    hello();

    a=0;
    hello();

    a=1;
    hello();

    while(1);
    }

    At optimisation level 0 my .cod file was as follows:

    ----- FUNCTION hello (BEGIN) -----
    FILE: 'junk.c'
    32: void hello(void)
    33: {
    34: volatile char b=1;
    35:
    00000F 750801 MOV b,#01H
    36: b++;
    000012 0508 INC b
    37: }
    000014 22 RET
    ----- FUNCTION hello (END) -------


    ----- FUNCTION main (BEGIN) -----
    FILE: 'junk.c'
    39: main()
    40: {
    41:
    42: a=1;
    000015 D200 SETB a
    43: hello();
    000017 110F ACALL hello
    44:
    45: a=0;
    000019 C200 CLR a
    46: hello();
    00001B 110F ACALL hello
    47:
    48: a=1;
    00001D D200 SETB a
    49: hello();
    00001F 110F ACALL hello
    50:
    51: a=0;
    000021 C200 CLR a
    52: hello();
    000023 110F ACALL hello
    53:
    54: a=1;
    000025 D200 SETB a
    55: hello();
    000027 110F ACALL hello
    56:
    57: a=0;
    000029 C200 CLR a
    58: hello();
    00002B 110F ACALL hello
    59:
    60: a=1;
    00002D D200 SETB a
    61: hello();
    00002F 110F ACALL hello
    000031 ?C0002?JUNK:
    62:
    63: while(1);
    000031 80FE SJMP ?C0002?JUNK
    64: }
    000033 22 RET
    ----- FUNCTION main (END) -------

    which doesn't show any optimisation at all.

    I think you must really be compiling with a higher level of optimisation than zero.

    Stefan

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