[PATCH 2/6] x86: shrink some struct insn_template fields

H.J. Lu hjl.tools@gmail.com
Mon Mar 29 14:41:41 GMT 2021


On Mon, Mar 29, 2021 at 7:03 AM Jan Beulich <jbeulich@suse.com> wrote:
>
> On 29.03.2021 15:00, H.J. Lu wrote:
> > On Fri, Mar 26, 2021 at 3:50 AM Jan Beulich <jbeulich@suse.com> wrote:
> >>
> >> Now that all base opcodes are only at most 2 bytes in size, shrink its
> >> template field to just as much. By also shrinking extension_opcode and
> >> operands to just what they really need, we can free up an entire 32-bit
> >> slot (plus 4 left bits past the bitfields themselves).
> >>
> >> At present this alters sizeof(struct insn_template) only for 32-bit
> >> builds. In 64-bit builds it instead leaves a padding hole that will
> >> allow to buffer future growth of other fields (opcode_modifier,
> >> cpu_flags, operand_types[]).
> >>
> >> opcodes/
> >> 2021-03-XX  Jan Beulich  <jbeulich@suse.com>
> >>
> >>         * i386-opc.h (struct insn_template): Shrink base_opcode to 16
> >>         bits. Shrink extension_opcode to 9 bits. Make it signed. Change
> >>         value of None. Shrink operands to 3 bits.
> >> ---
> >> Code-generation wise it may be better to move the signed
> >> extension_opcode field last within the containing 32-bit slot.
> >
> > extension_opcode should be next to opcode in template.
>
> In the source table, in the binary representation, or both? (I certainly
> agree they should be next to each other in the source table.)

Only in the source code, not in the binary representation.

-- 
H.J.


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