> >> bits 64
> >> mov rax,80000000h
> >> ... which should be capable of generate a 7-bit form.
> > Ahem... which particular encoding do you have in mind?
> > (It can't be 48,C7,C0,00,00,00,80 -- because 8000_0000
> > is not equal to sign-extended 8000_0000.)
> Sorry... brainfart on my part.
> I meant, of course, "mov rax,0FFFFFFFF80000000h".
> "mov rax,80000000h" should be reducable to the 5-byte
> "mov eax,80000000h" encoding.
That one would be legal.
I would expect the mov rax,... encoding be default, and
the mov eax,... encoding when that sort of optimization
was explicitly requested.