https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99408
--- Comment #2 from Jan Hubicka <hubicka at gcc dot gnu.org> ---
This also reproduces with zen4 and double.
jh@alberti:~/tsvc/bin> cat tt.c
typedef double real_t;
#define iterations 100000
#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];
void
main(void)
{
for (int nl = 0; nl < iterations; nl++) {
for (int i = 0; i < LEN_1D-1; i++){
a[i+1] = b[i]+c[i];
b[i] = c[i]*e[i];
d[i] = a[i]*e[i];
}
}
}
jh@alberti:~/tsvc/bin> ~/trunk-install/bin/gcc -Ofast -march=native tt.c
jh@alberti:~/tsvc/bin> time ./a.out
real 0m3.590s
user 0m3.585s
sys 0m0.004s
jh@alberti:~/tsvc/bin> clang -Ofast -march=native tt.c
tt.c:6:1: warning: return type of 'main' is not 'int' [-Wmain-return-type]
void
^
tt.c:6:1: note: change return type to 'int'
void
^~~~
int
1 warning generated.
jh@alberti:~/tsvc/bin> time ./a.out
real 0m1.538s
user 0m1.538s
sys 0m0.000s
gcc generates:
│ 60: vmovapd 0x67e080(%rax),%zmm7
0.15 │ vmovapd 0x601080(%rax),%zmm2
1.07 │ add $0x40,%rax
│ vaddpd 0x6bc840(%rax),%zmm7,%zmm0
0.00 │ vmovupd %zmm0,0x6fb048(%rax)
11.10 │ vmulpd 0x601040(%rax),%zmm7,%zmm0
9.46 │ vmovapd %zmm0,0x6bc840(%rax)
0.01 │ vmulpd 0x6fb040(%rax),%zmm2,%zmm0
78.20 │ vmovapd %zmm0,0x63f840(%rax)
│ cmp $0x3e7c0,%rax
│ ↑ jne 60
clang generates:
│ nop
│ a0: vmovupd (%r9,%rdx,1),%zmm15
0.46 │ vmovupd (%r9,%rdi,1),%zmm19
0.22 │ vmovupd 0x40(%r9,%rdx,1),%zmm16
0.56 │ vmovupd 0x40(%r9,%rdi,1),%zmm22
0.92 │ vmovupd 0x80(%r9,%rdx,1),%zmm17
1.85 │ vmovupd 0x80(%r9,%rdi,1),%zmm21
1.51 │ vaddpd (%r9,%rcx,1),%zmm15,%zmm18
0.84 │ vmulpd %zmm15,%zmm19,%zmm15
0.47 │ vmovupd %zmm15,(%r9,%rcx,1)
3.37 │ vaddpd 0x40(%r9,%rcx,1),%zmm16,%zmm15
0.56 │ vmulpd %zmm16,%zmm22,%zmm16
0.69 │ vmovupd %zmm16,0x40(%r9,%rcx,1)
3.82 │ vmovupd %zmm18,0x8(%r9,%rsi,1)
3.27 │ vmovapd %zmm15,%zmm20
│ vmovupd %zmm15,0x48(%r9,%rsi,1)
3.60 │ vpermt2pd %zmm18,%zmm13,%zmm20
0.47 │ vpermt2pd %zmm14,%zmm13,%zmm18
0.36 │ vmulpd %zmm19,%zmm18,%zmm18
1.07 │ vmulpd %zmm22,%zmm20,%zmm14
1.33 │ vmovupd %zmm18,(%r9,%r8,1)
6.31 │ vmovupd %zmm14,0x40(%r9,%r8,1)
8.02 │ vaddpd 0x80(%r9,%rcx,1),%zmm17,%zmm14
0.53 │ vmovapd %zmm14,%zmm16
0.05 │ vmovupd %zmm14,0x88(%r9,%rsi,1)
3.08 │ vpermt2pd %zmm15,%zmm13,%zmm16
0.41 │ vmulpd %zmm17,%zmm21,%zmm15
0.20 │ vmovupd %zmm15,0x80(%r9,%rcx,1)
1.60 │ vmulpd %zmm21,%zmm16,%zmm15
1.16 │ vmovupd %zmm15,0x80(%r9,%r8,1)
3.13 │ add $0xc0,%r9
│ cmp $0x3e7c0,%r9
0.03 │ ↑ jne a0
So a forward-dependency here?
