Merced (first generation Itanium) had hilariously bad performance, and its built in "x86 support" was even slower.

HP-designed later cores were much faster and omitted x86 hardware support replacing it with software emulation if needed, but ultimately IA-64 rarely ever ran with good performance as far as I know.

Pretty sure it was Itanium that finally turned "Sufficiently Smart Compiler" into curse phrase as it is understood today, and definitely popularized it.