# Speed of array intrinsics

**URL:** <https://fortran-lang.discourse.group/t/speed-of-array-intrinsics/3251>\
**Category:** Uncategorized\
**Created:** [April 17, 2022, 1:56pm UTC](https://fortran-lang.discourse.group/t/speed-of-array-intrinsics/3251 "2022-04-17T13:56:41Z")\
**Posts on this page:** 1\
**Showing post:** 10

<div class="post-metadata">

**Author:** ![ivanpribec](https://yyz2.discourse-cdn.com/free1/user_avatar/fortran-lang.discourse.group/ivanpribec/32/3290_2.png) [@ivanpribec](https://fortran-lang.discourse.group/u/ivanpribec)\
**Post date:** [April 12, 2025, 10:23am UTC](https://fortran-lang.discourse.group/t/speed-of-array-intrinsics/3251/10 "2025-04-12T10:23:00Z")

</div>

Recently I tested the speed of minloc between compilers. The test was essentially this:

```fortran
call get_command_argument(1,str)
read(str,*) n

allocate(a(n))
call random_number(a)

call system_clock(t1,count_rate=rate)
idx = minloc(a,dim=1)
call system_clock(t2)
print *, idx, a(idx), "built-in", real(t2 - t1)/rate

```

For `n = 10000000` I got the following results, measured on an Intel(R) Xeon(R) Platinum 8380 CPU,

[![](https://global.discourse-cdn.com/free1/uploads/fortran_lang/original/2X/7/7150fc0f667c16a5ef0952b67f3db209292d4225.png) ](https://global.discourse-cdn.com/free1/uploads/fortran_lang/original/2X/7/7150fc0f667c16a5ef0952b67f3db209292d4225.png)

The flags were the following:

| Compiler | Time (s) | Flags |
| --- | --- | --- |
| nagfor 7.2 | 1.75E-02 | `-O4 -target=native` |
| ifx 2025.1.0 | 4.39E-03 | `-O2 -xHOST` |
| ifx 2025.1.0 | 3.31E-03 | `-O2 -xHOST -mprefer-vector-width=512` |
| ifort 18.0.5 | 3.51E-03 | `-O2 -xHOST` |
| ifort 18.0.5 | **3.06E-03** | `-O2 -xHOST -qopt-zmm-usage=high` |
| ifort 17.0.6 | 3.16E-03 | `-O2 -xHOST -qopt-zmm-usage=high` |
| gfortran 12.2 | 1.76E-02 | `-O2 -march=native` |
| flang-new 19.1.1 | 5.76E-02 | `-O2 -march=native` |
| nvfortran 23.3-0 | 2.48E-02 | `-fast -mcpu=native` |

Interestingly, `ifort` has a very fast minloc that uses SIMD registers. In ifx the performance was worse, however in the oneAPI 2025 release, `ifx` once again has a fast minloc. When compiled with `-mprefer-vector-width=512` it uses AVX512 registers as seen from the following hot loop:

```auto
.LBB0_12:
	vmovups	(%rsi,%rax,4), %zmm7
	vpbroadcastq	%rax, %zmm8
	vcmpltps	%zmm3, %zmm7, %k1
	vpaddq	%zmm4, %zmm8, %zmm1 {%k1}
	kshiftrw	$8, %k1, %k2
	vpaddq	%zmm5, %zmm8, %zmm2 {%k2}
	vpmovqd	%zmm8, %ymm8
	vmovdqa	%ymm8, %ymm9
	vinserti64x4	$1, %ymm8, %zmm9, %zmm8
	vpaddd	%zmm6, %zmm8, %zmm0 {%k1}
	vminps	%zmm3, %zmm7, %zmm3
	addq	$16, %rax
	cmpq	%rdx, %rax
	jb	.LBB0_12

```

I first noticed that ifort has a fast minloc/maxloc implementation here: [Performance of vectorized code in ifort and ifx - #21 by ivanpribec](https://fortran-lang.discourse.group/t/performance-of-vectorized-code-in-ifort-and-ifx/7783/21)

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