From: John Lu <jlu@lsil.com>
To: gcc@gcc.gnu.org
Subject: Register Allocation
Date: Fri, 26 Mar 2004 22:21:00 -0000 [thread overview]
Message-ID: <200403261954.i2QJsfT27909@dts0.lsil.com> (raw)
Hi,
I've been working on a port based on gcc-3.3 and I've noticed that
better assembly code is generated if the C source has
separate variables declared for distinct live ranges.
For example,
int foo1(int *p1, int *p2) {
int i; /* one index variable for two live ranges */
int total;
total=0;
for (i=0; i<100; i++) {
total+=p1[i];
}
for (i=0; i<100; i+=2) {
total+=p1[i];
}
return(total);
}
produces worse code than:
int foo2(int *p1, int *p2) {
int i1,i2; /* two index variables for two live ranges */
int total;
total=0;
for (i1=0; i1<100; i1++) {
total+=p1[i1];
}
for (i2=0; i2<100; i2+=2) {
total+=p1[i2];
}
return(total);
}
In my port, i1 is allocated a loop register which supports faster looping,
and i2 is allocated to a gpr because a decrement by two is needed. When
only one index variable is declared, "i" is allocated to a loop register,
but this creates bad code for the second loop, since decrement by two is
not supported for loop registers. This happens with and without the
"-fnew-ra" option.
I was wondering if anyone else has seen this or am I doing something wrong
in my port.
Thanks,
John Lu
next reply other threads:[~2004-03-26 19:54 UTC|newest]
Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-03-26 22:21 John Lu [this message]
2004-03-26 22:21 ` Vladimir N. Makarov
2004-03-26 22:26 ` Andrew MacLeod
2004-03-27 18:22 ` Andi Kleen
-- strict thread matches above, loose matches on Subject: below --
2010-12-23 8:13 register allocation roy rosen
2010-12-23 16:48 ` Vladimir Makarov
2010-12-23 17:22 ` Jeff Law
2010-12-27 15:43 ` roy rosen
2011-01-03 15:41 ` Jeff Law
2011-01-05 14:44 ` roy rosen
2011-01-05 15:26 ` Jeff Law
2011-01-11 16:11 ` Vladimir Makarov
2011-01-11 15:53 ` Vladimir Makarov
2005-11-24 20:51 Register Allocation Joern RENNECKE
2005-11-17 16:53 Andrew MacLeod
2005-11-18 2:55 ` Mark Mitchell
2005-11-18 3:27 ` Daniel Jacobowitz
2005-11-18 9:53 ` Giovanni Bajo
2005-11-18 15:28 ` Andrew MacLeod
2005-11-19 19:31 ` Ian Lance Taylor
2005-11-19 20:20 ` Denis Chertykov
2005-11-20 0:20 ` Giovanni Bajo
2005-11-23 17:07 ` Andrew MacLeod
2005-11-23 20:43 ` Ian Lance Taylor
2005-11-20 0:37 ` Steven Bosscher
2005-11-23 17:08 ` Andrew MacLeod
2005-11-22 19:26 ` Peter Bergner
2005-11-22 21:55 ` Steven Bosscher
[not found] ` <200511222256.13823.>
2005-11-22 22:58 ` Peter Bergner
2005-11-23 14:06 ` Michael Matz
2005-11-23 20:50 ` Peter Bergner
2005-11-23 17:08 ` Andrew MacLeod
2004-09-22 1:21 Adrian Strätling
2004-09-22 5:22 ` tm_gccmail
2004-10-04 14:13 ` Nick Ing-Simmons
2004-05-02 13:27 register allocation Qiong Cai
2004-05-02 16:56 ` Daniel Berlin
2004-05-03 7:07 ` Michael Matz
2002-03-12 6:21 register Allocation Danish Samad
1997-10-14 5:51 Register allocation Thomas Koenig
1998-12-21 22:38 ` Jeffrey A Law
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