Re: [Qemu-devel] [PATCH 03/13] target-mips: refactor {D}LSA, {D}ALIGN, {D}BITSWAP

[Leon Alrae <leon.alrae@imgtec.com>]

On 12/06/2015 15:02, Yongbok Kim wrote:
> Refactor those instructions in order to reuse them for microMIPS32
> Release 6.
> 
> Signed-off-by: Yongbok Kim <yongbok.kim@imgtec.com>
> ---
>  target-mips/translate.c |  164 +++++++++++++++++++++++++++++-----------------
>  1 files changed, 103 insertions(+), 61 deletions(-)
> 
> diff --git a/target-mips/translate.c b/target-mips/translate.c
> index b8c7164..2244630 100644
> --- a/target-mips/translate.c
> +++ b/target-mips/translate.c
> @@ -4831,6 +4831,102 @@ static void gen_bshfl (DisasContext *ctx, uint32_t op2, int rt, int rd)
>      tcg_temp_free(t0);
>  }
>  
> +static void gen_lsa(DisasContext *ctx, int opc, int rd, int rs, int rt,
> +        int imm2)

Indentation is unusual.

> +{
> +    TCGv t0;
> +    TCGv t1;
> +    if (rd == 0) {
> +        /* Treat as NOP. */
> +        return;
> +    }
> +    t0 = tcg_temp_new();
> +    t1 = tcg_temp_new();
> +    gen_load_gpr(t0, rs);
> +    gen_load_gpr(t1, rt);
> +    tcg_gen_shli_tl(t0, t0, imm2 + 1);
> +    switch (opc) {
> +    case OPC_LSA:
> +        tcg_gen_add_tl(t0, t0, t1);
> +        tcg_gen_ext32s_tl(cpu_gpr[rd], t0);
> +        break;
> +#if defined(TARGET_MIPS64)
> +    case OPC_DLSA:
> +        tcg_gen_add_tl(cpu_gpr[rd], t0, t1);
> +        break;
> +#endif

The only difference between LSA and DLSA is that LSA sign extends the value
from bit 31.

Wouldn't it be better to replace this switch with:

tcg_gen_add_tl(cpu_gpr[rd], t0, t1);
if (opc == OPC_LSA) {
    tcg_gen_ext32s_tl(cpu_gpr[rd], cpu_gpr[rd]);
}

> +    }
> +    tcg_temp_free(t1);
> +    tcg_temp_free(t0);
> +
> +    return;
> +}
> +
> +static void gen_align(DisasContext *ctx, int opc, int rd, int rs, int rt,
> +        int bp)
> +{
> +    TCGv t0;
> +    if (rd == 0) {
> +        /* Treat as NOP. */
> +        return;
> +    }
> +    t0 = tcg_temp_new();
> +    gen_load_gpr(t0, rt);
> +    if (bp == 0) {
> +        tcg_gen_mov_tl(cpu_gpr[rd], t0);
> +    } else {
> +        TCGv t1 = tcg_temp_new();
> +        gen_load_gpr(t1, rs);
> +        switch (opc) {
> +        case OPC_ALIGN:
> +            {
> +                TCGv_i64 t2 = tcg_temp_new_i64();
> +                tcg_gen_concat_tl_i64(t2, t1, t0);
> +                tcg_gen_shri_i64(t2, t2, 8 * (4 - bp));
> +#if defined(TARGET_MIPS64)
> +                tcg_gen_ext32s_i64(cpu_gpr[rd], t2);
> +#else
> +                tcg_gen_trunc_i64_i32(cpu_gpr[rd], t2);
> +#endif

This can be replaced with gen_move_low32().

> +                tcg_temp_free_i64(t2);
> +            }
> +            break;
> +#if defined(TARGET_MIPS64)
> +        case OPC_DALIGN:
> +            tcg_gen_shli_tl(t0, t0, 8 * bp);
> +            tcg_gen_shri_tl(t1, t1, 8 * (8 - bp));
> +            tcg_gen_or_tl(cpu_gpr[rd], t1, t0);
> +            break;
> +#endif
> +        }
> +        tcg_temp_free(t1);
> +    }
> +
> +    tcg_temp_free(t0);
> +}
> +
> +static void gen_bitswap(DisasContext *ctx, int opc, int rd, int rt)
> +{
> +    TCGv t0;
> +    if (rd == 0) {
> +        /* Treat as NOP. */
> +        return;
> +    }
> +    t0 = tcg_temp_new();
> +    gen_load_gpr(t0, rt);
> +    switch (opc) {
> +    case OPC_BITSWAP:
> +        gen_helper_bitswap(cpu_gpr[rd], t0);
> +        break;
> +#if defined(TARGET_MIPS64)
> +    case OPC_DBITSWAP:
> +        gen_helper_dbitswap(cpu_gpr[rd], t0);
> +        break;
> +#endif
> +    }
> +    tcg_temp_free(t0);
> +}
> +
>  #ifndef CONFIG_USER_ONLY
>  /* CP0 (MMU and control) */
>  static inline void gen_mfc0_load32 (TCGv arg, target_ulong off)
> @@ -16191,18 +16287,7 @@ static void decode_opc_special_r6(CPUMIPSState *env, DisasContext *ctx)
>      op1 = MASK_SPECIAL(ctx->opcode);
>      switch (op1) {
>      case OPC_LSA:
> -        if (rd != 0) {
> -            int imm2 = extract32(ctx->opcode, 6, 3);
> -            TCGv t0 = tcg_temp_new();
> -            TCGv t1 = tcg_temp_new();
> -            gen_load_gpr(t0, rs);
> -            gen_load_gpr(t1, rt);
> -            tcg_gen_shli_tl(t0, t0, imm2 + 1);
> -            tcg_gen_add_tl(t0, t0, t1);
> -            tcg_gen_ext32s_tl(cpu_gpr[rd], t0);
> -            tcg_temp_free(t1);
> -            tcg_temp_free(t0);
> -        }
> +        gen_lsa(ctx, op1, rd, rs, rt, extract32(ctx->opcode, 6, 2));

Thanks for fixing the bug, length is indeed 2. It worked because additional
bit we read here was always 0.

>          break;
>      case OPC_MULT ... OPC_DIVU:
>          op2 = MASK_R6_MULDIV(ctx->opcode);
> @@ -16247,17 +16332,7 @@ static void decode_opc_special_r6(CPUMIPSState *env, DisasContext *ctx)
>  #if defined(TARGET_MIPS64)
>      case OPC_DLSA:
>          check_mips_64(ctx);
> -        if (rd != 0) {
> -            int imm2 = extract32(ctx->opcode, 6, 3);
> -            TCGv t0 = tcg_temp_new();
> -            TCGv t1 = tcg_temp_new();
> -            gen_load_gpr(t0, rs);
> -            gen_load_gpr(t1, rt);
> -            tcg_gen_shli_tl(t0, t0, imm2 + 1);
> -            tcg_gen_add_tl(cpu_gpr[rd], t0, t1);
> -            tcg_temp_free(t1);
> -            tcg_temp_free(t0);
> -        }
> +        gen_lsa(ctx, op1, rd, rs, rt, extract32(ctx->opcode, 6, 2));
>          break;
>      case R6_OPC_DCLO:
>      case R6_OPC_DCLZ:
> @@ -16682,35 +16757,15 @@ static void decode_opc_special3_r6(CPUMIPSState *env, DisasContext *ctx)
>                  /* Treat as NOP. */
>                  break;
>              }
> -            TCGv t0 = tcg_temp_new();
> -            gen_load_gpr(t0, rt);
> -
>              op2 = MASK_BSHFL(ctx->opcode);
>              switch (op2) {
>              case OPC_ALIGN ... OPC_ALIGN_END:
> -                sa &= 3;
> -                if (sa == 0) {
> -                    tcg_gen_mov_tl(cpu_gpr[rd], t0);
> -                } else {
> -                    TCGv t1 = tcg_temp_new();
> -                    TCGv_i64 t2 = tcg_temp_new_i64();
> -                    gen_load_gpr(t1, rs);
> -                    tcg_gen_concat_tl_i64(t2, t1, t0);
> -                    tcg_gen_shri_i64(t2, t2, 8 * (4 - sa));
> -#if defined(TARGET_MIPS64)
> -                    tcg_gen_ext32s_i64(cpu_gpr[rd], t2);
> -#else
> -                    tcg_gen_trunc_i64_i32(cpu_gpr[rd], t2);
> -#endif
> -                    tcg_temp_free_i64(t2);
> -                    tcg_temp_free(t1);
> -                }
> +                gen_align(ctx, OPC_ALIGN, rd, rs, rt, sa & 3);
>                  break;
>              case OPC_BITSWAP:
> -                gen_helper_bitswap(cpu_gpr[rd], t0);
> +                gen_bitswap(ctx, op2, rd, rt);
>                  break;
>              }
> -            tcg_temp_free(t0);
>          }
>          break;
>  #if defined(TARGET_MIPS64)
> @@ -16727,29 +16782,16 @@ static void decode_opc_special3_r6(CPUMIPSState *env, DisasContext *ctx)
>                  /* Treat as NOP. */
>                  break;
>              }
> -            TCGv t0 = tcg_temp_new();
> -            gen_load_gpr(t0, rt);
> -
>              op2 = MASK_DBSHFL(ctx->opcode);
>              switch (op2) {
>              case OPC_DALIGN ... OPC_DALIGN_END:
> -                sa &= 7;
> -                if (sa == 0) {
> -                    tcg_gen_mov_tl(cpu_gpr[rd], t0);
> -                } else {
> -                    TCGv t1 = tcg_temp_new();
> -                    gen_load_gpr(t1, rs);
> -                    tcg_gen_shli_tl(t0, t0, 8 * sa);
> -                    tcg_gen_shri_tl(t1, t1, 8 * (8 - sa));
> -                    tcg_gen_or_tl(cpu_gpr[rd], t1, t0);
> -                    tcg_temp_free(t1);
> -                }
> +                gen_align(ctx, OPC_DALIGN, rd, rs, rt, sa & 7);
>                  break;
>              case OPC_DBITSWAP:
> -                gen_helper_dbitswap(cpu_gpr[rd], t0);
> +                gen_bitswap(ctx, op2, rd, rt);
>                  break;
>              }
> -            tcg_temp_free(t0);
> +
>          }
>          break;
>  #endif
>