RE: [avr-gcc-list] Code size optimization

[Dave Hansen]

From: Antony MATRANGA <address@hidden>
[...]
> The compiler is smart enough to insert RET instruction when it's usefull
> but not enough when it's useless.
>
> see:
> void lcd_interf_RESET (BOOL Level)
> {
>   if (Level)
>     1eac:       88 23           and     r24, r24
>     1eae:       11 f0           breq    .+4             ; 0x1eb4
>   {
>     PORTB |= _BV(PB1);
>     1eb0:       29 9a           sbi     0x05, 1 ; 5
>     1eb2:       08 95           ret
>   }
>   else
>   {
>     PORTB &= ~_BV(PB1);
>     1eb4:       29 98           cbi     0x05, 1 ; 5
>     1eb6:       08 95           ret
>     1eb8:       08 95           ret
>   }
> }
>
> compiling on :
> avr-gcc -gdwarf-2 -Wall -O2 -mmcu=atmega168  -fshort-enums -mtiny-stack  -c 
> -o
> lcd_interf.o lcd_interf.c
>
> In this case I think the last RET should be removed.
> I a 8k application, i'm loosing 12 bytes. And one byte is one byte

I think your'e using the wrong optimization level.  I created a small test 
file from your example:

--- begin included file ---

  C:\Dave>type opt.c
  #include <avr/io.h>
  typedef unsigned char BOOL;

  void lcd_interf_RESET (BOOL Level)
  {
    if (Level)
    {
      PORTB |= _BV(PB1);
    }
    else
    {
      PORTB &= ~_BV(PB1);
    }
  }

  C:\Dave>avr-gcc -mmcu=atmega16 -Os -S opt.c

  C:\Dave>type opt.s
          .file   "opt.c"
          .arch atmega16
  __SREG__ = 0x3f
  __SP_H__ = 0x3e
  __SP_L__ = 0x3d
  __tmp_reg__ = 0
  __zero_reg__ = 1
          .global __do_copy_data
          .global __do_clear_bss
          .text
  .global lcd_interf_RESET
          .type   lcd_interf_RESET, @function
  lcd_interf_RESET:
  /* prologue: frame size=0 */
  /* prologue end (size=0) */
          tst r24
          breq .L2
          sbi 56-0x20,1
          ret
  .L2:
          cbi 56-0x20,1
          ret
  /* epilogue: frame size=0 */
  /* epilogue: noreturn */
  /* epilogue end (size=0) */
  /* function lcd_interf_RESET size 6 (6) */
          .size   lcd_interf_RESET, .-lcd_interf_RESET
  /* File "opt.c": code    6 = 0x0006 (   6), prologues   0, epilogues   0 
*/

  C:\Dave>avr-gcc -v
  Reading specs from C:/WinAVR/bin/../lib/gcc/avr/3.4.1/specs
  Configured with: ../gcc-3.4.1/configure --prefix=e:/avrdev/install 
--build=mingw
  32 --host=mingw32 --target=avr --enable-languages=c,c++
  Thread model: single
  gcc version 3.4.1

  C:\Dave>

--- end included file ---

The extraneous "ret" is gone.  HTH,
  -=Dave