From: Thomas Koenig <ig25@mvmap66.ciw.uni-karlsruhe.de>
To: egcs@cygnus.com
Subject: Register allocation
Date: Tue, 14 Oct 1997 05:51:00 -0000 [thread overview]
Message-ID: <199710141250.NAA03152@mvmap66.ciw.uni-karlsruhe.de> (raw)
egcs 971008 with haifa enabled generates two unnecessary register
moves for the function for Linux i386-glibc1:
typedef struct pt
{
int x;
int y;
struct pt *n;
} pt;
#define WALL(a) ((a)->n == 0)
#define SQR(a) ((double) (a)* (double) (a))
double e_point_point(pt *a, pt *b)
{
double res;
res = SQR(a->x - b->x) + SQR(a->y - b->y);
if (WALL(a) || WALL(b)) {
res *= 4;
}
return res;
}
Here's the assembly output:
.file "point.c"
.version "01.01"
/ GNU C version egcs-2.90.12 971008 (gcc2-970802 experimental) (i586-pc-linux-gnulibc1) compiled by GNU C version egcs-2.90.12 971008 (gcc2-970802 experimental).
/ options passed: -O6 -fomit-frame-pointer -fno-exceptions
/ options enabled: -fdefer-pop -fomit-frame-pointer -fcse-follow-jumps
/ -fcse-skip-blocks -fexpensive-optimizations -fthread-jumps
/ -fstrength-reduce -fpeephole -fforce-mem -ffunction-cse
/ -finline-functions -finline -fkeep-static-consts -fcaller-saves
/ -fpcc-struct-return -frerun-cse-after-loop -fschedule-insns2
/ -fsched-interblock -fsched-spec -fcommon -fverbose-asm -fgnu-linker
/ -fregmove -falias-check -fargument-alias -m80387 -mhard-float
/ -mno-soft-float -mieee-fp -mfp-ret-in-387 -mschedule-prologue
/ -mcpu=pentium -march=pentium
gcc2_compiled.:
.section .rodata
.align 4
.LC1:
.long 0x0,0x40100000
.text
.align 4
.globl e_point_point
.type e_point_point,@function
e_point_point:
pushl %ebx
movl 8(%esp),%edx
movl 12(%esp),%ecx
movl (%edx),%ebx
movl (%ecx),%eax
fmul %st(0),%st
subl %eax,%ebx
movl %ebx,%eax
^^^^^^^^^^^^^^
pushl %eax
fildl (%esp)
addl $4,%esp
fmul %st(0),%st
faddp %st,%st(1)
cmpl $0,8(%edx)
je .L3
cmpl $0,8(%ecx)
jne .L2
.L3:
fldl .LC1
fmulp %st,%st(1)
.L2:
popl %ebx
ret
.Lfe1:
.size e_point_point,.Lfe1-e_point_point
.ident "GCC: (GNU) egcs-2.90.12 971008 (gcc2-970802 experimental)"
Both of these register moves are unnecessary, and when I replace the
first one with the more obvious
subl %eax,%ebx
pushl %ebx
movl 4(%edx),%ebx
fildl (%esp)
the resulting code is indeed faster.
--
Thomas Koenig, Thomas.Koenig@ciw.uni-karlsruhe.de, ig25@dkauni2.bitnet.
The joy of engineering is to find a straight line on a double
logarithmic diagram.
next reply other threads:[~1997-10-14 5:51 UTC|newest]
Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top
1997-10-14 5:51 Thomas Koenig [this message]
1998-12-21 22:38 ` Jeffrey A Law
2002-03-12 6:21 register Allocation Danish Samad
2004-03-26 22:21 Register Allocation John Lu
2004-03-26 22:21 ` Vladimir N. Makarov
2004-03-26 22:26 ` Andrew MacLeod
2004-03-27 18:22 ` Andi Kleen
2004-05-02 13:27 register allocation Qiong Cai
2004-05-02 16:56 ` Daniel Berlin
2004-05-03 7:07 ` Michael Matz
2004-09-22 1:21 Register Allocation Adrian Strätling
2004-09-22 5:22 ` tm_gccmail
2004-10-04 14:13 ` Nick Ing-Simmons
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
2005-11-24 20:51 Joern RENNECKE
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
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