[avr-gcc-list] Peculiar code size problem

[Parthasaradhi Nayani]

Hi all,

I am working on an ATMEGA8. Since my code was getting close to 8K, I thought I would tweak the code. I have a function listed below

void pulse_en (void)

{

  set_EN; // Set EN

  _delay_loop_1 (255);

  clr_EN; // clear EN

 _delay_loop_1 (255);

}

Since the delay after the "clr" instruction had no meaning, I commented the line and compiled the code hoping I would save a couple of bytes. But to my surprise the code size increased to 7172 bytes compared to 7148 bytes with the function call in place. I looked at the list file and found that the function gets shifted to a different location with and without the function call. Here are the list file snippets

With the call in place:

351               pulse_en:

 352               .LFB23:

 353               .LM47:

 354               /* prologue: function */

 355               /* frame size = 0 */

 356               .LM48:

 357 0128 C29A       sbi 56-32,2

 358               .LBB80:

 359               .LBB81:

 360               .LM49:

 361 012a 8FEF       ldi r24,lo8(-1)

 362 012c 982F       mov r25,r24

 363               .LVL17:

 364               /* #APP */

 365               ;  83 "c:/winavr-20100110/lib/gcc/../../avr/include/util/delay_basic.h" 1

 366 012e 9A95       1: dec r25

 367 0130 01F4       brne 1b

 368               ;  0 "" 2

 369               /* #NOAPP */

 370               .LBE81:

 371               .LBE80:

 372               .LM50:

 373 0132 C298       cbi 56-32,2

 374               .LBB82:

 375               .LBB83:

 376               .LM51:

 377               /* #APP */

 378               ;  83 "c:/winavr-20100110/lib/gcc/../../avr/include/util/delay_basic.h" 1

 379 0134 8A95       1: dec r24

 380 0136 01F4       brne 1b

 381               ;  0 "" 2

 382               .LVL18:

 383               /* epilogue start */

 384               /* #NOAPP */

 385               .LBE83:

 386               .LBE82:

 387               .LM52:

 388 0138 0895       ret

Without the call:

621               .LFE21:

 623               .global pulse_en

 625               pulse_en:

 626               .LFB23:

 627               .LM87:

 628               /* prologue: function */

 629               /* frame size = 0 */

 630               .LM88:

 631 01c2 C29A       sbi 56-32,2

 632               .LBB146:

 633               .LBB147:

 634               .LM89:

 635 01c4 8FEF       ldi r24,lo8(-1)

 636               .LVL36:

 637               /* #APP */

 638               ;  83 "c:/winavr-20100110/lib/gcc/../../avr/include/util/delay_basic.h" 1

 639 01c6 8A95       1: dec r24

 640 01c8 01F4       brne 1b

 641               ;  0 "" 2

 642               /* #NOAPP */

 643               .LBE147:

 644               .LBE146:

 645               .LM90:

 646 01ca C298       cbi 56-32,2

 647               /* epilogue start */

 648               .LM91:

 649 01cc 0895       ret

Will some one please let me know why this is happening? If such is the case, perhaps extra code is being generated for other function too. 

I am using: avr-gcc (WinAVR 20100110) 4.3.3

 

Thank you for your time.

Regards,
Nayani