Apart from Clang/LLVM and WebKit you mean?
Ok in fairness the LGPL license of KHTML was a huge reason the WebKit source was available (for ages it was just reluctant tarball dumps) but I don't think that's the case for LLVM.
I don't think the GPL has really meant corporation's have given back significantly to Linux. There are still plenty of closed source drivers. The main motivation to give back is the extremely high cost of maintaining out-of-tree modifications (e.g. Android's binder).
The compiler and toolchain really are going the wrong direction with LLVM in terms of open source.
And hey some of the work does get upstreamed, which is probably a good choice for the vendor anyway if the target in question isn't intended to be immediately thrown in the thrash and forgotten.
It was originally supposed to. https://lists.gnu.org/archive/html/emacs-devel/2015-02/msg00...