> Itanium failed because brilliant compilers didn't exist and it was barely faster even with hand-tuned code, especially when you adjusted for cost, but that doesn't mean that it doesn't matter at all.

What you said is true for libraries, I just don't think it's true for compiler optimizations. Even Apple's clang just doesn't have any new optimizations that work on their own; there are certainly new features but they're usually intrinsics and other things that need to be adopted by hand. They thought this would happen (it's what bitcode was sold as doing) but in practice it has not happened.