Fedora Looks To Build Firefox With Clang For Better Performance & Compilation Speed

[Weasel]

Why is it that the minute LLVM/CLang is mentioned in any post a bunch of nervous nellies have to chime in all concerned about why GCC was left out? In this case it is likely more about Rust, debugging support and other factors beyond performance that makes the changes reasonable to the Firefox team. Even then the delta between the two compiler chains is minor when running C++ code, with GCC's biggest wins being for features Firefox doesn't even use.

Because you call bullshit for what it is. Even the title says that it's for "performance".

[Marc Driftmeyer]

In five years Firefox will be so niche you won't remember it. Why? Corporations I'm running across on the internet, like Schedulicity and more already have announced denying future support for Firefox and request people switch to Chrome or Safari. This came a day after Microsoft announced ending Edge and building a custom Chrome for Windows.

Pretty soon Firefox will go the way of Opera.

[KellyClowers]

I care less about if they use Clang or GCC and more about if they are going to move to some kind of sane build system, like cmake or meson

[Weasel]

In five years Firefox will be so niche you won't remember it. Why? Corporations I'm running across on the internet, like Schedulicity and more already have announced denying future support for Firefox and request people switch to Chrome or Safari. This came a day after Microsoft announced ending Edge and building a custom Chrome for Windows.

Pretty soon Firefox will go the way of Opera.

It deserves it because of Rust.

[lsatenstein]

I have come code that segment issues if built with CLANG, and does not have then if built with gcc.
I also encounter the reverse. Clang based compile crashes and gcc does not.

Regarding sizes. The differences between clang or gcc is 100 or so bytes. I cannot judge which of the two produces faster executing code.

[hubicka]

I tried to get some real data about performance built with recent GCC and Clang with LTO+PGO. You can also download the binary and test it yourself. Seems to me that GCC wins especially in code size and performance. Clang has edge in compile time and memory use.

http://hubicka.blogspot.com/2018/12/firefox-64-built-with-gcc-and-clang.html

[ms178]

I tried to get some real data about performance built with recent GCC and Clang with LTO+PGO. You can also download the binary and test it yourself. Seems to me that GCC wins especially in code size and performance. Clang has edge in compile time and memory use.
http://hubicka.blogspot.com/2018/12/...and-clang.html

Thank you very much for that informative comparison, Honza!