http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41076
Georg-Johann Lay <gjl at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|RESOLVED |REOPENED
Resolution|FIXED |
Target Milestone|4.7.1 |---
Severity|enhancement |normal
--- Comment #6 from Georg-Johann Lay <gjl at gcc dot gnu.org> 2013-01-22
22:31:11 UTC ---
(In reply to comment #5)
> Fixed I suppose.
Unfortunately, not
extern unsigned char read8 (void);
unsigned short read16 (void)
{
unsigned char lo, hi;
hi = read8();
lo = read8();
return lo | hi << 8;
}
with 4.8.0 -S -Os the compiler needs 5 instructions (29, 37, 30, 38) for an
operation that is basically a no-op:
read16:
push r28 ; 31 pushqi1/1 [length = 1]
/* prologue: function */
/* frame size = 0 */
/* stack size = 1 */
.L__stack_usage = 1
call read8 ; 5 call_value_insn/2 [length = 2]
mov r28,r24 ; 6 movqi_insn/1 [length = 1]
call read8 ; 7 call_value_insn/2 [length = 2]
mov r18,r28 ; 28 movqi_insn/1 [length = 1]
ldi r19,0 ; 29 movqi_insn/1 [length = 1]
mov r19,r18 ; 37 *ashlhi3_const/3 [length = 2]
clr r18
or r18,r24 ; 30 iorqi3/1 [length = 1]
movw r24,r18 ; 38 *movhi/1 [length = 1]
/* epilogue start */
pop r28 ; 34 popqi [length = 1]
ret ; 35 return_from_epilogue [length = 1]
