Re: [PATCH v5 1/6] tcg/sparc: Add scratch argument to tcg_out_movi_int

[Peter Maydell]

On Sun, 6 Feb 2022 at 10:31, Richard Henderson
<richard.henderson@linaro.org> wrote:
>
> This will allow us to control exactly what scratch register is
> used for loading the constant.  Also, fix a theoretical problem
> in recursing through tcg_out_movi, which may provide a different
> value for in_prologue.
>
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
> ---
>  tcg/sparc/tcg-target.c.inc | 21 +++++++++++++--------
>  1 file changed, 13 insertions(+), 8 deletions(-)
>
> diff --git a/tcg/sparc/tcg-target.c.inc b/tcg/sparc/tcg-target.c.inc
> index 0c062c60eb..8c3671f56a 100644
> --- a/tcg/sparc/tcg-target.c.inc
> +++ b/tcg/sparc/tcg-target.c.inc
> @@ -414,7 +414,8 @@ static void tcg_out_movi_imm13(TCGContext *s, TCGReg ret, 
> int32_t arg)
>  }
>
>  static void tcg_out_movi_int(TCGContext *s, TCGType type, TCGReg ret,
> -                             tcg_target_long arg, bool in_prologue)
> +                             tcg_target_long arg, bool in_prologue,
> +                             TCGReg scratch)
>  {
>      tcg_target_long hi, lo = (int32_t)arg;
>      tcg_target_long test, lsb;
> @@ -471,22 +472,25 @@ static void tcg_out_movi_int(TCGContext *s, TCGType 
> type, TCGReg ret,
>      /* A 64-bit constant decomposed into 2 32-bit pieces.  */
>      if (check_fit_i32(lo, 13)) {
>          hi = (arg - lo) >> 32;
> -        tcg_out_movi(s, TCG_TYPE_I32, ret, hi);
> +        tcg_out_movi_int(s, TCG_TYPE_I32, ret, hi, in_prologue, scratch);
>          tcg_out_arithi(s, ret, ret, 32, SHIFT_SLLX);
>          tcg_out_arithi(s, ret, ret, lo, ARITH_ADD);
>      } else {
> +        tcg_debug_assert(scratch != TCG_REG_G0);
>          hi = arg >> 32;
> -        tcg_out_movi(s, TCG_TYPE_I32, ret, hi);
> -        tcg_out_movi(s, TCG_TYPE_I32, TCG_REG_T2, lo);
> +        tcg_out_movi_int(s, TCG_TYPE_I32, ret, hi, in_prologue, scratch);
> +        tcg_out_movi_int(s, TCG_TYPE_I32, scratch, lo, in_prologue, 
> TCG_REG_G0);
>          tcg_out_arithi(s, ret, ret, 32, SHIFT_SLLX);
> -        tcg_out_arith(s, ret, ret, TCG_REG_T2, ARITH_OR);
> +        tcg_out_arith(s, ret, ret, scratch, ARITH_OR);
>      }
>  }
>
>  static void tcg_out_movi(TCGContext *s, TCGType type,
>                           TCGReg ret, tcg_target_long arg)
>  {
> -    tcg_out_movi_int(s, type, ret, arg, false);
> +    /* When outputting to T2, we have no scratch available. */
> +    TCGReg scratch = ret != TCG_REG_T2 ? TCG_REG_T2 : TCG_REG_G0;

Why won't using G0 trip the assertion above that scratch != TCG_REG_G0 ?

> +    tcg_out_movi_int(s, type, ret, arg, false, scratch);
>  }
>

-- PMM