LLVM and GCC are so close together these days that it makes almost no difference practically, and when it does you should start optimizing based around your code not your compiler.
Dude I mean the context in which I'm discussing this is a large organization operating on timescales shorter than microseconds with numerous people involved in optimizing every single part of the pipeline. We are waaaaaaaaaaay past the point of "premature" optimization. This is just optimization, and optimization where a few percent difference between compilers is huge.
Your comments read like you're explaining optimization to a beginner, it's a bit bad faith tbh.
GCC and LLVM have broadly similar performance characteristics(i.e. for any arch/uBenchmark combo there is another that puts the other one faster).
If GCC is appreciably faster for your purpose, then fair enough but LLVM is not drastically slow by any means (Especially when you consider that any "Anything you can do..." Between LLVM and GCC moves much faster on the LLVM side due to a much saner codebase)
You are talking about it like comparing a Ford to a VW they are pretty much the same, but what the poster above talks about is more like comparing formula 1 cars where a single percent of engine power can win or lose you the race. The difference may be small enough for by far the most purposes, but this one is where the small difference can cost a lot.
Root of all evil etc. etc.