------- Additional Comments From Thomas dot Koenig at online dot de 2005-02-14
20:06 -------
Same thing for complex division, where the performance
penalty is probably also pretty severe:
$ cat c-div.c
#include <math.h>
#include <complex.h>
int main()
{
float a;
complex float b,c;
foo(&a,&b);
c = b/a;
return creal(c) + cimag(c) < 0;
}
$ gcc -fdump-tree-all-all -O3 -S c-div.c
$ tail -20 c-div.c.t65.optimized
complex floatD.25 c.20D.2363;
complex floatD.25 c.19D.2362;
intD.0 D.2361;
complex floatD.25 D.2360;
complex floatD.25 D.2359;
floatD.21 a.18D.2358;
# BLOCK 0
# PRED: ENTRY [100.0%] (fallthru,exec)
# aD.2354_25 = V_MAY_DEF <aD.2354_1>;
# bD.2355_26 = V_MAY_DEF <bD.2355_5>;
foo (&aD.2354, &bD.2355);
# D.2360_11 = V_MUST_DEF <D.2360_10>;
D.2360 = __divsc3 (REALPART_EXPR <bD.2355>, IMAGPART_EXPR <bD.2355>,
aD.2354,0.0);
return (doubleD.22) REALPART_EXPR <D.2360> + (doubleD.22) IMAGPART_EXPR
<D.2360> < 0.0;
# SUCC: EXIT [100.0%]
}
Addition has the same problem. Here, a floating point register is
carefully zeroed in order to add something to it:
$ cat c-add.c
#include <math.h>
#include <complex.h>
int main()
{
float a;
complex float b,c;
foo(&a,&b);
c = b+a;
return creal(c) + cimag(c) < 0;
}
$ gcc -fdump-tree-all-all -O3 -S c-add.c
$ tail -20 c-add.c.t65.optimized
doubleD.22 D.2365;
floatD.21 D.2364;
complex floatD.25 c.20D.2363;
complex floatD.25 c.19D.2362;
intD.0 D.2361;
complex floatD.25 D.2360;
complex floatD.25 D.2359;
floatD.21 a.18D.2358;
# BLOCK 0
# PRED: ENTRY [100.0%] (fallthru,exec)
# aD.2354_27 = V_MAY_DEF <aD.2354_1>;
# bD.2355_28 = V_MAY_DEF <bD.2355_7>;
foo (&aD.2354, &bD.2355);
return (doubleD.22) (aD.2354 + REALPART_EXPR <bD.2355>) + (doubleD.22)
(IMAGPART_EXPR <bD.2355> + 0.0) < 0.0;
# SUCC: EXIT [100.0%]
}
$ tail -20 c-add.s
leal -4(%ebp), %eax
movl %eax, (%esp)
call foo
flds -12(%ebp)
fldz
fadds -8(%ebp)
fxch %st(1)
fadds -4(%ebp)
leave
faddp %st, %st(1)
fldz
fucompp
fnstsw %ax
testb $69, %ah
sete %al
movzbl %al, %eax
ret
.size main, .-main
.ident "GCC: (GNU) 4.0.0 20050212 (experimental)"
.section .note.GNU-stack,"",@progbits
If somebody tackles this, it would also be nice if purely
imaginary numbers were also special-cased.
--
What |Removed |Added
----------------------------------------------------------------------------
Summary|Special-case real*complex |Special-case real + complex
|multiplication for |arithmetic operation
|flag_complex_method=2 |
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19953
