From: Uros Bizjak <uros@kss-loka.si>
To: gcc@gcc.gnu.org
Subject: Missing if optimization
Date: Thu, 09 Sep 2004 05:24:00 -0000 [thread overview]
Message-ID: <413FE7D1.8000201@kss-loka.si> (raw)
Hello!
The if optimization, which produces quite optimized code for integer
case is missing for floatin-point compares.
This code:
int test(int a) {
return a == 0 ? 0 : (a > 0 ? 1 : -1);
}
produces (with -O2 -fomit-frame-pointer):
test:
xorl %eax, %eax
cmpl $0, 4(%esp)
je .L4
setg %al
movzbl %al, %eax
leal -1(%eax,%eax), %eax
.L4:
ret
However, fp compares:
double testf(double a) {
return a == 0.0 ? 0.0 : (a > 0.0 ? 1.0 : -1.0);
}
Produce somehow unoptimized code (-O2 -ffast-math -fomit-frame-pointer):
testf:
fldl 4(%esp)
ftst
fnstsw %ax
sahf
jne .L9
fstp %st(0)
fldz
ret
.p2align 4,,7
.L9:
ftst
fnstsw %ax
fstp %st(0)
sahf
ja .L12
flds .LC1
ret
.p2align 4,,7
.L12:
fld1
.p2align 4,,2
ret
There is no need for second fp compare, two conditional jumps after
first fp compare would be enough.
Uros.
next reply other threads:[~2004-09-09 5:24 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-09-09 5:24 Uros Bizjak [this message]
2004-09-09 5:49 ` Andrew Pinski
2004-09-09 22:15 ` James E Wilson
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