Re: [PATCH 1/3] tcg/i386: Drop BYTEH deposits for 64-bit

[Richard Henderson]

On 8/17/23 08:44, Peter Maydell wrote:
> On Wed, 16 Aug 2023 at 16:01, Richard Henderson
> <richard.henderson@linaro.org> wrote:
> > It is more useful to allow low-part deposits into all registers
> > than to restrict allocation for high-byte deposits.
>
> >   #define TCG_TARGET_deposit_i32_valid(ofs, len) \
> > -    (((ofs) == 0 && (len) == 8) || ((ofs) == 8 && (len) == 8) || \
> > -     ((ofs) == 0 && (len) == 16))
> > +    (((ofs) == 0 && ((len) == 8 || (len) == 16)) || \
> > +     (TCG_TARGET_REG_BITS == 32 && (ofs) == 8 && (len) == 8))
> >   #define TCG_TARGET_deposit_i64_valid    TCG_TARGET_deposit_i32_valid
>
>
> > @@ -2752,7 +2751,7 @@ static inline void tcg_out_op(TCGContext *s, TCGOpcode 
> > opc,
> >           if (args[3] == 0 && args[4] == 8) {
> >               /* load bits 0..7 */
> >               tcg_out_modrm(s, OPC_MOVB_EvGv | P_REXB_R | P_REXB_RM, a2, a0);
> > -        } else if (args[3] == 8 && args[4] == 8) {
> > +        } else if (TCG_TARGET_REG_BITS == 32 && args[3] == 8 && args[4] == 8) {
>
> Should we assert(TCG_TARGET_REG_BITS == 32) rather than making it part of the
> condition?

The if/else chain ends in g_assert_not_reached().

> If I understand the change to the deposit_i32_valid macro above, we
> should never get here with 8, 8 if TCG_TARGET_REG_BITS is 64.

Correct.


r~