From: "Paulo J. Matos" <pocmatos@gmail.com>
To: gcc@gcc.gnu.org
Subject: avr compilation
Date: Fri, 18 Mar 2011 08:48:00 -0000 [thread overview]
Message-ID: <ilv67b$au6$1@dough.gmane.org> (raw)
Hi all,
I am looking at the avr backend in order to try to sort some things out
on my own backend.
One of the tests I am doing is by compiling the following:
int x = 0x1010;
int y = 0x0101;
int add(void)
{
return x+y;
}
It compiles to (in gcc-4.3.5_avr with -Os)
add:
/* prologue: function */
/* frame size = 0 */
lds r18,y
lds r19,(y)+1
lds r24,x
lds r25,(x)+1
add r18,r24
adc r19,r25
mov r24,r18
mov r25,r19
/* epilogue start */
ret
I don't know much avr assembler so bear with me but I would expect this
to be written:
add:
/* prologue: function */
/* frame size = 0 */
lds r18,y
lds r19,(y)+1
lds r24,x
lds r25,(x)+1
add r24,r18
adc r25,r19
/* epilogue start */
ret
By inverting the add arguments we save two mov instructions.
If it can be written like this any ideas on why GCC is avoiding it?
Cheers,
--
PMatos
next reply other threads:[~2011-03-18 8:48 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-03-18 8:48 Paulo J. Matos [this message]
2011-03-18 10:08 ` WANG.Jiong
2011-03-18 10:15 ` Paulo J. Matos
2011-03-18 12:11 ` David Brown
2011-03-18 13:37 ` Paulo J. Matos
2011-03-18 13:26 ` Georg-Johann Lay
2011-03-18 13:40 ` Paulo J. Matos
2011-03-18 14:20 ` Ian Lance Taylor
2011-03-18 14:50 ` Paulo J. Matos
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