Looking at the following piece of code:
#include <math.h>
#include <complex.h>
int main()
{
float a;
complex float b,c;
foo(&a, &b);
c = a*b;
return creal(c)+cimag(c)<0;
}
and compiling this with flag_complex_method=2 and -O3, I find
that the statement is translated to (in t65.optimized) to
# BLOCK 0
# PRED: ENTRY [100.0%] (fallthru,exec)
# aD.2211_25 = V_MAY_DEF <aD.2211_1>;
# bD.2212_26 = V_MAY_DEF <bD.2212_7>;
foo (&aD.2211, &bD.2212);
# D.2217_11 = V_MUST_DEF <D.2217_10>;
D.2217 = __mulsc3 (aD.2211, 0.0, REALPART_EXPR <bD.2212>, IMAGPART_EXPR
<bD.2212>);
return (doubleD.24) REALPART_EXPR <D.2217> + (doubleD.24) IMAGPART_EXPR
<D.2217> < 0.0;
# SUCC: EXIT [100.0%]
This costs quite a lot of performance. Multiplying a real number
by a complex number doesn't require any special cases, so the whole
__mulsc3 machinery is not needed here.
$ gcc -v
Using built-in specs.
Target: ia64-unknown-linux-gnu
Configured with: ../gcc-4.0-20050213/configure --prefix=/home/zfkts
--enable-languages=c,f95
Thread model: posix
gcc version 4.0.0 20050213 (experimental)
--
Summary: Special-case real*complex multiplication for
flag_complex_method=2
Product: gcc
Version: 4.0.0
Status: UNCONFIRMED
Severity: normal
Priority: P2
Component: middle-end
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: Thomas dot Koenig at online dot de
CC: gcc-bugs at gcc dot gnu dot org
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19953
