Decreased NVC analysis and simulation speed between 1.19.1 and 1.19.3

[Paebbels]

Since OSVVM 2026.01, we can visualize multiple simulations runs on an overview page. Here, OSVVM records the used simulator version.

I see that 1.19.0 and 1.19.1 were almost 2x faster than the current 1.19.3 release.
I have no data for 1.19.2.

The comparison has been done with PoC Library and OsvvmLibraries. Both show the same behavior. In all cases, the used OSVVM and OSVVM scripting version was 2026.01. The DUT and testbenches were not changed in between.

OsvvmLibraries	PoC Library

Does NVC test it's speed or are speed parameters recorded over time (e.g. runtime of the NVC testsuite on GitHub)?

Until now, NVC was the fastest VHDL simulator to my knowledge. Also faster than commercial simulators. It would be bad if NVC gets slower 😞.

[nickg]

Is this on Windows? On my system for time OSVVM_MUST_BUILD=1 nvc --do ~/nvc/test/test-osvvm.tcl (which builds and runs all the OSVVM tests) I get:

master  2m21.088s
1.19.3  2m23.036s
1.19.1  2m21.426s

That's with the previous version of OSVVM though.

Does NVC test it's speed or are speed parameters recorded over time (e.g. runtime of the NVC testsuite on GitHub)?

I track performance on a variety of benchmarks, both real-world and synthetic, so I'm surprised something like this could slip though. Admittedly that's only for simulation time and only on Linux.

I'm wondering if this could be caused by some change in the build environment on GHA between those two releases (e.g. the LLVM version). Can you paste the output of nvc --version in both cases?

[Paebbels]

Yes, my tests are on Windows (local laptop - Alienware gaming PC - Core Ultra 9 185H).

I used the official MSI installers for 1.19.0, 1.19.1 and 1.19.3
1.19.3 reports:

nvc 1.19.3 (1.19.3.r0.g72fecb933) (Using LLVM 21.1.8)
Copyright (C) 2011-2026  Nick Gasson
This program comes with ABSOLUTELY NO WARRANTY. This is free software, and
you are welcome to redistribute it under certain conditions. See the GNU
General Public Licence for details.

Should I install again some of the older versions and rerun it? Usually, I update NVC in the default installation location with the latest version. I use nvc --do to use its internal scripting and have no overhead by tclsh or similar.

[nickg]

I tried the following on a Windows VM:

Measure-Command { nvc --do C:\msys64\home\nick\nvc\test\test-osvvm.tcl }

With the MSI from the 1.19.1 release:

...
TotalSeconds      : 258.4183157
...

And the 1.19.3 release:

...
TotalSeconds      : 252.3935765
...

I had to modify VendorScripts_NVC.tcl a bit to run it from PowerShell though:

diff --git a/VendorScripts_NVC.tcl b/VendorScripts_NVC.tcl
index 4ed9976482a5..ea0bd1ec4b4a 100644
--- a/VendorScripts_NVC.tcl
+++ b/VendorScripts_NVC.tcl
@@ -63,7 +63,7 @@
     # running on MSYS2 - convert which with cygpath
     set nvc [exec cygpath -m [exec which nvc]]
   } else {
-    set nvc [exec which nvc]
+    set nvc "C:/Program Files/NVC/bin/nvc.exe"
   }

   regexp {nvc\s+\d+\.\d+\S*} [exec $nvc --version] VersionString

Do you have any way of generating a smaller reproducer for this?

[Paebbels]

Sorry, I was a few days off (and offline). I'll install a few NVC versions in parallel and check why my PC reports differences. I'll come back to you with detailed reports from my side.

[Paebbels]

Hmmm, once 1.20.0 is installed, I can't install 1.19.0 anymore. The installer aborts with an error message popup and immediately goes to the last page. Is there any flag to override this behavior?

[Paebbels]

Moreover, when I install version 1.19.[0..3] in C:\Tools\NVC, they get uninstalled, thus I can't have multiple versions in parallel :(.

[nickg]

Moreover, when I install version 1.19.[0..3] in C:\Tools\NVC, they get uninstalled, thus I can't have multiple versions in parallel :(.

This is a "feature" of MSI packages: https://learn.microsoft.com/en-us/windows/win32/msi/installing-multiple-instances-of-products-and-patches

See also #1429

To downgrade I believe you can just uninstall the current version and then install the old one.

[Paebbels]

You're right. I believe I never needed to install programs parallel for multiple versions when the program was MSI distributed :). I'll uninstall the latest. Install again from 1.19.0 to 1.20.0 and run my tests in between... argh

[nickg]

A solution to this is to use msiexec to extract the files and then copy them where you want.

PS C:\Users\nick\Downloads> msiexec /a nvc-1.19.3.msi TARGETDIR=C:\Temp
PS C:\Users\nick\Downloads> dir C:\Temp\PFiles\


    Directory: C:\Temp\PFiles


Mode                 LastWriteTime         Length Name
----                 -------------         ------ ----
d-----        18/04/2026     08:35                NVC


PS C:\Users\nick\Downloads> dir C:\Temp\PFiles\NVC\


    Directory: C:\Temp\PFiles\NVC


Mode                 LastWriteTime         Length Name
----                 -------------         ------ ----
d-----        18/04/2026     08:35                bin
d-----        18/04/2026     08:35                include
d-----        18/04/2026     08:35                lib
d-----        18/04/2026     08:35                libexec
d-----        18/04/2026     08:35                share

We don't install any registry keys so the directory is completely self contained and can be moved around.