RE: [avr-gcc-list] Wrong excution order in 4.1.1, but not 3.4.5,regression?

[Eric Weddington]

Hi Bob,

I can't fully tell what's going on with just the asm snippets you provide.

If you think that this is a GCC bug, then please fill out a GCC bug report.

Thanks for checking the known bug list first. :-)

If you fill in a GCC bug report, feel free to put my email address on the CC
list of the bug report.

Thanks,
Eric Weddington 

> -----Original Message-----
> From: 
> address@hidden 
> [mailto:address@hidden
> org] On Behalf Of Bob Paddock
> Sent: Monday, February 19, 2007 2:49 PM
> To: address@hidden
> Subject: [avr-gcc-list] Wrong excution order in 4.1.1, but 
> not 3.4.5,regression?
> 
> 
> I'm seeing something in 4.1.1 that is not making
> sense.  The code produced is clearly the wrong
> order, in 4.1.1.  Code from 3.4.5 is the correct order.
> 
> Optimization in both cases is set for -Os;
> I'm using the same source code/Makfile and
> pointing at different versions of WINAVR,
> between 4.1.1 and 3.4.5.
> 
> I've looked at the known problem list, but
> I could not related this to any of those.
> http://www.nongnu.org/avr-libc/bugs.html
> 
> I can't seem to get a good cut down example
> that produces the error.  The code
> effectively looks like this:
> 
> static volatile PGM_UP  pattern_flash_ptr_u8_v; /* IRQ 
> updates PORTB */
> static volatile PGM_UP  pattern_flash_ptr_reload_u8_v;
> [PGM_UP is unsigned version of PGM_P.]
> 
>        do{
>          pattern_flash_ptr_u8_v = 
> pattern_flash_ptr_reload_u8_v = (PGM_UP)  
> pgm_read_word( &pattern_table[ 0 ] );
>        }while( mode_button_press_count_u8 < max_button_presses_u8 );
> 
> In the real code 'mode_button_press_count_u8' actually could
> change its value inside of the do{}while(),
> and the pattern_table[ 0 ] index would
> be a variable.  I made these changes to the real code,
> and the problem persists.
> 
> For:
> 
>   pattern_flash_ptr_u8_v = pattern_flash_ptr_reload_u8_v = (PGM_UP)  
> pgm_read_word( &pattern_table[ 0 ] );
> 
>   4.1.1 produces:
> 
>   3ca:        e6 e8           ldi     r30, 0x86       ; 134 
> [Address of pattern_table]
>   3cc:        f0 e0           ldi     r31, 0x00       ; 0
>   3ce:        c8 95           lpm
>   3d0:        c0 2d           mov     r28, r0
>   3d2:        31 96           adiw    r30, 0x01       ; 1
>   3d4:        c8 95           lpm
>   3d6:        d0 2d           mov     r29, r0
>   3d8:        0c 2f           mov     r16, r28  [Missed 
> optimization, but that is  
> separate matter for an other time.  r16/r17 was loaded above 
> only to be  
> overwritten here, and not needed below.]
>   3da:        1d 2f           mov     r17, r29
>   3dc:        ff 20           and     r15, r15
>   3de:        c9 f6           brne    .-78            ; 0x392 
> <main+0x74> [Jump to do{]
>   3e0:        10 93 7b 00     sts     0x007B, r17  [This is 
> outside of the do{}while() so  
> the code fails.]
>   3e4:        00 93 7a 00     sts     0x007A, r16
>   3e8:        d0 93 7d 00     sts     0x007D, r29
>   3ec:        c0 93 7c 00     sts     0x007C, r28
> 
> 
> 3.4.5 produces this, correct code:
> 
>              pattern_flash_ptr_u8_v = 
> pattern_flash_ptr_reload_u8_v =  
> (PGM_UP) pgm_read_word( &pattern_table[ 0 ] );
>   3ec:        ef e3           ldi     r30, 0x3F       ; 63  
> [Address of pattern_table]
>   3ee:        f0 e0           ldi     r31, 0x00       ; 0
>   3f0:        c8 95           lpm
>   3f2:        80 2d           mov     r24, r0
>   3f4:        31 96           adiw    r30, 0x01       ; 1
>   3f6:        c8 95           lpm
>   3f8:        90 2d           mov     r25, r0
>   3fa:        90 93 80 00     sts     0x0080, r25 [This is 
> inside the do{}while(), code  
> works.  Doesn't have optimization issues either.]
>   3fe:        80 93 7f 00     sts     0x007F, r24
>   402:        90 93 7e 00     sts     0x007E, r25
>   406:        80 93 7d 00     sts     0x007D, r24
>            }
> 
>        }while( mode_button_press_count_u8 < max_button_presses_u8 );
>   40a:        90 91 79 00     lds     r25, 0x0079
>   40e:        80 91 60 00     lds     r24, 0x0060
>   412:        98 17           cp      r25, r24
>   414:        08 f4           brcc    .+2             ; 0x418 
> <main+0xdc> [Exit do{}while]
>   416:        c5 cf           rjmp    .-118           ; 0x3a2 
> <main+0x66> [Jump to do{]
> 
> 
> 
> 
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