Re: [PATCH v3 04/24] tcg/i386: Tidy register constraint definitions

[Peter Maydell]

On Fri, 29 Jan 2021 at 20:14, Richard Henderson
<richard.henderson@linaro.org> wrote:
>
> Create symbolic constants for all low-byte-addressable
> and second-byte-addressable registers.  Create a symbol
> for the registers that need reserving for softmmu.
>
> There is no functional change for 's', as this letter is
> only used for i386.  The BYTEL name is correct for the
> action we wish from the constraint.
>
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
> ---
>  tcg/i386/tcg-target.c.inc | 40 +++++++++++++++++++--------------------
>  1 file changed, 20 insertions(+), 20 deletions(-)
>
> @@ -226,11 +234,11 @@ static const char 
> *target_parse_constraint(TCGArgConstraint *ct,
>          break;
>      case 'q':
>          /* A register that can be used as a byte operand.  */
> -        ct->regs = TCG_TARGET_REG_BITS == 64 ? 0xffff : 0xf;
> +        ct->regs |= ALL_BYTEL_REGS;
>          break;
>      case 'Q':
>          /* A register with an addressable second byte (e.g. %ah).  */
> -        ct->regs = 0xf;
> +        ct->regs |= ALL_BYTEH_REGS;
>          break;
>      case 'r':
>          /* A general register.  */
> @@ -247,19 +255,11 @@ static const char 
> *target_parse_constraint(TCGArgConstraint *ct,
>
>      case 'L':
>          /* qemu_ld/st data+address constraint */
> -        ct->regs = TCG_TARGET_REG_BITS == 64 ? 0xffff : 0xff;
> -#ifdef CONFIG_SOFTMMU
> -        tcg_regset_reset_reg(ct->regs, TCG_REG_L0);
> -        tcg_regset_reset_reg(ct->regs, TCG_REG_L1);
> -#endif
> +        ct->regs |= ALL_GENERAL_REGS & ~SOFTMMU_RESERVE_REGS;
>          break;
>      case 's':
>          /* qemu_st8_i32 data constraint */
> -        ct->regs = 0xf;
> -#ifdef CONFIG_SOFTMMU
> -        tcg_regset_reset_reg(ct->regs, TCG_REG_L0);
> -        tcg_regset_reset_reg(ct->regs, TCG_REG_L1);
> -#endif
> +        ct->regs |= ALL_BYTEL_REGS & ~SOFTMMU_RESERVE_REGS;
>          break;

Should these cases really be ORing in these expressions
rather than just using '=' the way the old code was?

Otherwise
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>

thanks
-- PMM