ifx performance issues

[Umar__Sait]

There is a significany drop in performance between ifort and ifx. For Intel CPUs:

Intel(R) Xeon(R) Gold 6246R CPU @ 3.40GHz (16+16=32 core)

Intel ifort 2021.13.1
CFLAGS= -free -warn all -diag-disable=10448 -nogen-interfaces -no-prec-div -O3 -fp-model=fast=2 -xHost
real 124m20.650s
user 3049m40.783s
sys 10m40.430s

Intel ifx 2025.3.0
CFLAGS= -free -warn all -nogen-interfaces -O3 -xHost -qopenmp
real 162m36.896s
user 3966m5.817s
sys 12m34.195s

albeit faster than gfortran at 216m. The problem is double precision complex algebra. The code

is also using openmp.

In addition, ifort runs much faster on AMD CPU:

AMD Ryzen Threadripper PRO 7975WX @ 4.0GHz 32-Cores

Intel ifort 2021.13.1
CFLAGS= -free -warn all -nogen-interfaces -diag-disable=10448 -Ofast -march=SSE4.2,CORE-AVX2,znver4 -qopenmp

real 67m37.749s
user 1744m37.811s
sys 13m21.562s

Intel ifx 2025.3.0
CFLAGS= -free -warn all -nogen-interfaces -O3 -Ofast -march=znver4 -qopenmp

real 113m5.164s
user 2487m13.638s
sys 13m46.812s

Intel seems to have removed some of the optimization features for AMD processorts from

ifx....can't use SSE4.2,CORE-AVX2 anymore.....

[Igor_V_Intel]

Could you please share a code showing this performance drop?

Note that LLVM IR doesn't have complex data types and thus code with complex type algebra is a known issue vs ifort (there Intel had native complex type support on the proprietary IR level). It should be improved in the next major release of ifx.

[Umar__Sait]

This is a very large nuclear reactions code written in Fortran 95, so it is hard to share. Normally, in some cases the code has to be run for many days, even a week to get the answers. These were shorter runs for timing purposes. But one can see that all llvm based compilers are running slower than ifort. I am looking forward to the improvements you mention and hopefully we can switch to ifx at some point, but as you can see running for 5 days vs 10 days makes a big difference so we will stick with ifort until then.

[mecej4O]

The attached program conj11.f90 runs for about 1 second and produces a counterexample for the Euler Conjecture on the sum of fifth powers.

The EXEs generated using IFort consistently run faster than those produced by Ifx. I hope that this example code will help you to make Ifx produce EXEs that are not slower than those produced by Ifort.

Thanks.