https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108376
--- Comment #3 from Jan Hubicka <hubicka at gcc dot gnu.org> ---
If I make the arrays random then GCC code is indeed faster:
#include <math.h>
#include <malloc.h>
typedef float real_t;
#define iterations 1000000
#define LEN_1D 32000
#define LEN_2D 256
real_t a[LEN_1D],b[LEN_1D],c[LEN_1D],d[LEN_1D],e[LEN_1D];
real_t aa[LEN_2D][LEN_2D];
real_t bb[LEN_2D][LEN_2D];
real_t cc[LEN_2D][LEN_2D];
real_t qq;
int
main(void)
{
// reductions
// if to max reduction
real_t x;
for (int i = 0; i < LEN_1D; i++)
{
a[i]=(rand() %5) - 3;
b[i]=(rand() %6) - 3;
}
for (int nl = 0; nl < iterations; nl++) {
for (int i = 0; i < LEN_1D; i++) {
if (a[i] < (real_t)0.) {
if (b[i] > a[i]) {
c[i] += d[i] * e[i];
}
}
}
//dummy(a, b, c, d, e, aa, bb, cc, 0.);
}
return x;
}
jh@alberti:~/tsvc/bin> ~/aocc-compiler-4.0.0/bin/clang -Ofast s1279.c
-march=native
s1279.c:23:14: warning: implicit declaration of function 'rand' is invalid in
C99 [-Wimplicit-function-declaration]
a[i]=(rand() %5) - 3;
^
1 warning generated.
jh@alberti:~/tsvc/bin> time ./a.out
real 0m5.638s
user 0m5.636s
sys 0m0.000s
jh@alberti:~/tsvc/bin> ~/trunk-install/bin/gcc -Ofast s1279.c -march=native
s1279.c: In function 'main':
s1279.c:23:14: warning: implicit declaration of function 'rand'
[-Wimplicit-function-declaration]
23 | a[i]=(rand() %5) - 3;
| ^~~~
jh@alberti:~/tsvc/bin> time ./a.out
real 0m2.791s
user 0m2.790s
sys 0m0.000s
sorry for wrong code, just for reference the loop compiles as:
.L4:
xorl %eax, %eax
.p2align 4
.p2align 3
.L3:
vmovaps a(%rax), %ymm2
vmovaps b(%rax), %ymm3
vmovaps c(%rax), %ymm6
addq $32, %rax
vmovaps c-32(%rax), %ymm0
vmovaps e-32(%rax), %ymm4
vcmpps $1, %ymm1, %ymm2, %k1
vcmpps $14, %ymm2, %ymm3, %k1{%k1}
vfmadd231ps d-32(%rax), %ymm4, %ymm0{%k1}
vfmadd231ps d-32(%rax), %ymm4, %ymm0
vblendmps %ymm0, %ymm6, %ymm0{%k1}
vmovaps %ymm0, c-32(%rax)
cmpq $128000, %rax
jne .L3
decl %edx
jne .L4
