The eagle-eyed among you may have noticed a change in the way compiling using Microsoft Visual Studio compilers works on Compiler Explorer. Short version: we have gained execution support (yay), but lost library support (boo). We’re working on the latter.
So, what happened? In order to explain, here’s some background:
Compiler Explorer runs on Linux infrastructure. My day job for the last two decades has meant developing on, and for, Linux or Linux-based systems. As a result, CE itself uses Linux. When folks originally asked for Windows compiler support, I put it off for a while. A few years after, a friend helped me just about coerce and fudge a few versions of MSVC to run under WINE, but it’s not perfect and to this day causes us issues.
Microsoft reached out and offered to help. Through a number of conversations with the fine folks who work there, we negotiated an informal deal where they would run and administrate an instance of Compiler Explorer on Windows with access to their compilers. The main Compiler Explorer would transparently proxy to MS’s infrastructure and so users mostly wouldn’t know this was going on. That worked a treat and got us the latest Windows compilers, supported by professionals who had intimate understanding and knowledge of Windows and how to secure it.
Over the years, priorities and teams changed, and issues and concerns about security grew. Code execution had to be disabled, and the site became a little less reliable, with periods of downtime for the MSVC compilers ranging from hours to days. As most people didn’t know it was MS who were responsible for these compilers, and that the main CE team didn’t have any control or access to the MS side of things or its configuration, it was a little frustrating being “front line support” with no ability to fix things. Our friends at Microsoft were very helpful but also had many other priorities and considerations other than CE, so this is completely understandable.
Ultimately after a lot of discussion and hard work proving out and setting up our own Windows-based infrastructure (mostly by our star developer Patrick Quist), Microsoft agreed to help us host the compilers ourselves. I can’t go into more specifics due to the nature of the legal agreement between us.
So: now we get to install, maintain, host and secure the Windows Microsoft Visual Studio C and C++ compilers on Compiler Explorer. That is great for our users: we can be more responsive to issues and bug reports; we have been able to re-enable execution on Windows; and we can steer the direction as we see fit amongst the community.
However, we lost library support along the way: Microsoft chose to use their
own vcpkg-based solution for implementing libraries somewhat separately
from the way the rest of CE does libraries. That definitely made sense when
they had a free choice and separate infrastructure, but we have chosen not
to try and reproduce that setup. We are currently brainstorming
how best to deal with libraries for Windows: our Linux-based solution has
some novel Linux-only tricks to make it performant enough for interactivity
that we haven’t yet worked out Windows equivalents for.
Hopefully this explains the change in MSVC on Compiler Explorer. If you’re interested in learning more, or following further development, then check out:
Matt Godbolt is a C++ developer living in Chicago. Follow him on Mastodon or Bluesky.