> Everything else is basically irrelevant because as Clang has aged it's both slowed down and reached parity in both compile and execution speed. Phoronix even have GCC faster than Clang at building the Linux Kernel, even in an (according to a comment) biased sample where GCC wasn't built with lto enabled. GCC also (last time I tried) does better debug info.

It's entirely possible that the only reason GCC & Clang are so close is that both projects focused on places where the other project beat them & so have converged. Certainly the LTO work that's been going on is an obvious example where the two projects have learned & pushed each other. GCC's original LTO implementation was basically unusable. Then Clang released ThinLTO & GCC scrambled to add WHOPR (& by my reading of the blog posts the engineer(s) on it have done some amazing work to pull ahead of the Clang team at times).