# Intel's ifx significantly slower at compiling data heavy subroutine

**URL:** <https://fortran-lang.discourse.group/t/intels-ifx-significantly-slower-at-compiling-data-heavy-subroutine/10688>\
**Category:** Compilers\
**Created:** [February 2, 2026, 4:02pm UTC](https://fortran-lang.discourse.group/t/intels-ifx-significantly-slower-at-compiling-data-heavy-subroutine/10688 "2026-02-02T16:02:45Z")\
**Posts on this page:** 3\
**Page:** 1

<div class="post-metadata">

**Author:** ![abhro](https://yyz2.discourse-cdn.com/free1/user_avatar/fortran-lang.discourse.group/abhro/32/6882_2.png) [@abhro](https://fortran-lang.discourse.group/u/abhro)\
**Post date:** [February 2, 2026, 4:02pm UTC](https://fortran-lang.discourse.group/t/intels-ifx-significantly-slower-at-compiling-data-heavy-subroutine/10688/1 "2026-02-02T16:02:45Z")

</div>

For a data heavy subroutine, ifx takes noticeably longer than gfortran to compile.

Compiler versions

```plaintext
$ ifx --version
ifx (IFX) 2025.3.2 20260112
Copyright (C) 1985-2026 Intel Corporation. All rights reserved.

$ gfortran --version
GNU Fortran (Ubuntu 13.3.0-6ubuntu2~24.04) 13.3.0
Copyright (C) 2023 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

$ gfortran-14 --version
GNU Fortran (Ubuntu 14.2.0-4ubuntu2~24.04) 14.2.0
Copyright (C) 2024 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

```

Compilation times

```plaintext
$ time ifx mwe.f90 -o mwe-ifx
ifx mwe.f90 -o mwe-ifx 44.25s user 0.26s system 99% cpu 44.609 total

$ time gfortran mwe.f90 -o mwe-gfortran
gfortran mwe.f90 -o mwe-gfortran 0.17s user 0.06s system 83% cpu 0.279 total

$ time gfortran-14 mwe.f90 -o mwe-gfortran-14
gfortran-14 mwe.f90 -o mwe-gfortran-14 0.17s user 0.06s system 87% cpu 0.265 total

```

Runtime behavior

```plaintext
$ time ./mwe-ifx > ifx-output
./mwe-ifx > ifx-output 0.00s user 0.00s system 76% cpu 0.011 total

$ time ./mwe-gfortran > gfortran-output
./mwe-gfortran > gfortran-output 0.01s user 0.00s system 95% cpu 0.010 total

$ time ./mwe-gfortran-14 > gfortran-14-output
./mwe-gfortran-14 > gfortran-14-output 0.01s user 0.00s system 93% cpu 0.011 total

$ diff3 gfortran-14-output gfortran-output ifx-output

$ ls -l
total 1344
-rw-rw-r-- 1 user group 100200 Feb 1 17:22 gfortran-14-output
-rw-rw-r-- 1 user group 100200 Feb 1 17:22 gfortran-output
-rw-rw-r-- 1 user group 100200 Feb 1 17:22 ifx-output
-rw-rw-r-- 1 user group 114183 Feb 1 16:42 mwe.f90
-rwxrwxr-x 1 user group 113064 Feb 1 17:22 mwe-gfortran
-rwxrwxr-x 1 user group 113064 Feb 1 17:22 mwe-gfortran-14
-rwxrwxr-x 1 user group 721888 Feb 1 17:21 mwe-ifx

```

The source code for the program is at [slow-compile-mwe.f90 - Pastes.io](https://pastes.io/slow-compi) (the pastebin expires in 1 month, may edit the question to put the source code here once there’s enough reputation)

---

<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:** [February 2, 2026, 4:14pm UTC](https://fortran-lang.discourse.group/t/intels-ifx-significantly-slower-at-compiling-data-heavy-subroutine/10688/2 "2026-02-02T16:14:15Z")

</div>

> [@Oddly slow compilation of character data with ifx](https://fortran-lang.discourse.group/t/oddly-slow-compilation-of-character-data-with-ifx/8465/2):
>
> Compile-time compilation of constants and constructors is slower with Intel Fortran than gfortran and other Fortran compilers. It is due to the way our front-end handles compile-time constants. There was a discussion on this recently on numeric data. It is the same with numeric and character compile time constants. We made a few minor tweaks but not enough to make much difference. This is nothing we can fix, it is deeply embedded in how we parse and initialize constants with our front-end. …

---

<div class="post-metadata">

**Author:** ![abhro](https://yyz2.discourse-cdn.com/free1/user_avatar/fortran-lang.discourse.group/abhro/32/6882_2.png) [@abhro](https://fortran-lang.discourse.group/u/abhro)\
**Post date:** [February 7, 2026, 6:04pm UTC](https://fortran-lang.discourse.group/t/intels-ifx-significantly-slower-at-compiling-data-heavy-subroutine/10688/3 "2026-02-07T18:04:57Z")

</div>

[mwe.f90](https://fortran-lang.discourse.group/uploads/short-url/egFNv9IRCeuu26DjYNZc9Hpkjv.f90) (111.5 KB)  
Posting the source file also here as a reply for posterity.