From: "Dhananjay R. Deshpande" <dhananjayd@kpit.com>
To: <gcc@gcc.gnu.org>
Subject: FW: H8300 optimization
Date: Thu, 25 Jul 2002 10:18:00 -0000 [thread overview]
Message-ID: <69595093233BB547BB70CF5E492B63F2531601@sohm.kpit.com> (raw)
-----Original Message-----
From: Dhananjay R. Deshpande
Sent: Thursday, July 25, 2002 4:47 PM
To: 'gcc-bugs@gcc.gnu.org'
Subject: H8300 optimization
Hi,
I have a simple function which returns max of two unsigned integers.
unsigned int maxu(unsigned int a, unsigned int b)
{
return ( a > b ? a : b );
}
Compiling it with h8300-hms-gcc -S -O2 -fomit-frame-pointer gives -
.section .text
.align 1
.global _maxu
_maxu:
mov.w r0,r2
mov.w r1,r0
cmp.w r2,r1
bhs .L2
mov.w r2,r0
.L2:
rts
.end
.ident
"GCC: (GNU) 3.1"
Here use of r2 as scratch register is not required. One could write
cmp.w r1,r0
bhs .L2
mov.w r1,r0
.L2:
This could save 2 instructions. Is it possible to generate this sequence
from compiler?
I tried to understand from RTL dump how r2 comes into picture. It looks
like global reg alloc allocates r0 for b and r2 for a and this is causing
use of extra register and 2 extra instructions.
Regards,
Dhananjay
reply other threads:[~2002-07-25 11:29 UTC|newest]
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