Re: [PATCH] i386: Also check R12-R15 registers when optimizing testq to testb

["H.J. Lu" <hjl dot tools at gmail dot com>]

On Fri, Dec 13, 2019 at 2:13 AM Jan Beulich <jbeulich@suse.com> wrote:
>
> On 12.12.2019 21:31,  H.J. Lu  wrote:
> > Similar to SP, BP, SI and DI registers, R12-R15 registers must use REX
> > prefix for the low byte register when optimizing
>
> Wouldn't it be better (more generic) to fix the logic producing the
> diagnostic which gets in the way, seeing that generated code is
> actually correct:
>
>           /* Look for 8 bit operand that uses old registers.  */
>           if (i.types[x].bitfield.class == Reg && i.types[x].bitfield.byte
>               && !(i.op[x].regs->reg_flags & RegRex64)
>               && !(i.op[x].regs->reg_flags & RegRex))
>             {
>               /* In case it is "hi" register, give up.  */
>               if (i.op[x].regs->reg_num > 3)
>                 as_bad (_("can't encode register '%s%s' in an "
>                           "instruction requiring REX prefix."),
>                         register_prefix, i.op[x].regs->reg_name);
>
>
> ? This would then also make the code match both of the comments
> (which it doesn't right now).
>
>

This is an assembler implementation error.   Care to make a patch?

Thanks.

-- 
H.J.