[Bug c/34790] Missed optimisation on avr - no sibling call optimisation

["david at westcontrol dot com" <gcc-bugzilla at gcc dot gnu dot org>]

------- Comment #1 from david at westcontrol dot com  2008-01-15 08:34 -------
(Sorry - I committed the bug before entering the description!)

Sibling calls are not optimised on avrgcc, even with -foptimize-sibling-calls
enabled (such as for -Os):

extern void foo(void);
void bar(void) {
        foo();
}

  40                    bar:
  41                    /* prologue: frame size=0 */
  42                    /* prologue end (size=0) */
  43 0000 0E94 0000             call foo         ; 
  44                    /* epilogue: frame size=0 */
  45 0004 0895                  ret
  46                    /* epilogue end (size=1) */
  47                    /* function bar size 3 (2) */

Optimising the "call foo; ret" sequence to "jmp foo" would reduce the code size
by 1 word, the stack usage by 2 bytes (on most avrs), and save 5 cycles.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34790