Compile times of icx on Window super slow.

[Frank_R_1]

Hi,

We are using Intel oneAPI 2025.3.1 icx.exe with Visual Studio 2022 on Windows 11 Enterprise (Versions 22H2, 23H2, 24H2, 25H2),

with cmake 3.31.1 and ninja 1.13.1 for parallel builds.

We found out that the parallel execution of icx.exe seem to be serialized.

Please find attached icx_test.zip which contains a reproducer:

unzip icx_test.zip and open cmd.exe in that folder

call gen.bat to generate a src folder with 1000 .cxx files for parallel compile test

open howtorun.txt for instructions:

first section is for cl.exe

second section is for icx.exe

cl.exe compiles these 1000 .cxx files in under 5 seconds on my Xeon Gold 6416H.
icx.exe needs way too long for only 100 .cxx files.

Furthermore icx.png shows a call stack of one icx (clang) process during parallel compiling, it hangs there and waits.

Do we something wrong here?
On Intel oneAPI 2024.3 everything was fast, now it is barely unusable in parallel builds.

Best regards

Frank

[Frank_R_1]

If we do

set SystemRoot=

in the cmd.exe, then compilation is as fast as cl.exe!

What happens here?

Best regards

Frank

[Frank_R_1]

Hi,

We tested the example with original clang-cl.exe 21.1.0, and 21.1.8 and they are superfast in compiling these 1000 files.

We also compared the compiler images and they differ, especially in which functions are imported from libraries.

Does Intel alter the clang-cl.exe?

I would be very nice to get an answer or a hint for a workaround, because these compile times kill us in daily work.

Best regards

Frank

[Sravani_K_Intel]

Hi @Frank_R_1, 

The latest compiler in our development branch no longer has this issue. The 2026.0 version of the compiler is coming up next month, so I recommend upgrading to it when available. 

[Frank_R_1]

Hi,

Is this issue now fixed in Intel oneAPI 2025.3.2 (complete update from April 07th) or 2025.3.3 (special compiler update from March 24th)

Or will be a complete new Intel oneAPI package (base and hpc) called 2026.1.0?

Best regards

Frank

[Sravani_K_Intel]

The fix will be in the 2026.0 compiler, which will be released as part of the oneAPI 2026.0 package.