[PATCH 1/3] x86: Split REX/REX2 old registers judgment.
Jan Beulich
jbeulich@suse.com
Tue May 21 12:18:56 GMT 2024
On 20.05.2024 08:22, Cui, Lili wrote:
> --- a/gas/config/tc-i386.c
> +++ b/gas/config/tc-i386.c
> @@ -4303,22 +4303,20 @@ static void establish_rex (void)
> /* Respect a user-specified REX prefix. */
> i.rex |= i.prefix[REX_PREFIX] & REX_OPCODE;
>
> - /* For 8 bit registers we need an empty rex prefix. Also if the
> - instruction already has a prefix, we need to convert old
> - registers to new ones. */
> -
> - if ((i.types[first].bitfield.class == Reg && i.types[first].bitfield.byte
> - && ((i.op[first].regs->reg_flags & RegRex64) != 0 || i.rex != 0
> - || i.rex2 != 0))
> - || (i.types[last].bitfield.class == Reg && i.types[last].bitfield.byte
> - && ((i.op[last].regs->reg_flags & RegRex64) != 0 || i.rex != 0
> - || i.rex2 != 0)))
> - {
> - unsigned int x;
> -
> - if (!is_apx_rex2_encoding () && !is_any_vex_encoding(&i.tm))
> - i.rex |= REX_OPCODE;
> - for (x = first; x <= last; x++)
> + /* For 8 bit registers without a prefix, we need an empty rex prefix. */
As you're touching this comment, can you please also correct it? It's
not all 8-bit registers which are affected here (as expressed by the
RegRex64 checks).
> + if (((i.types[first].bitfield.class == Reg && i.types[first].bitfield.byte
> + && ((i.op[first].regs->reg_flags & RegRex64) != 0 ))
Nit: Please parenthesize this line and ...
> + || (i.types[last].bitfield.class == Reg && i.types[last].bitfield.byte
> + && (i.op[last].regs->reg_flags & RegRex64) != 0 ))
... this one the same way, preferably like the latter. Also please omit
the blanks before the closing parentheses.
> + && !is_apx_rex2_encoding () && !is_any_vex_encoding (&i.tm) && !i.rex)
Is the !i.rex part needed? It wasn't there before. If it's needed, it
would imo better come ahead of the APX/VEX checks.
> + i.rex |= REX_OPCODE;
> +
> + /* For REX/REX2 prefix instructions, we need to convert old registers
> + (AL, CL, DL and BL) to new ones (AXL, CXL, DXL and BXL) and report bad
> + for AH, CH, DH and BH. */
"report bad for" is a little odd; how about simply "reject"?
Okay with respective adjustments.
Jan
> + if (i.rex || i.rex2)
> + {
> + for (unsigned int x = first; x <= last; x++)
> {
> /* Look for 8 bit operand that uses old registers. */
> if (i.types[x].bitfield.class == Reg && i.types[x].bitfield.byte
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