Re: [Qemu-devel] [PATCH v6 2/7] target/mips: Support R5900 specific three-operand MULT and MULTU

[Philippe Mathieu-Daudé]

On 9/15/18 11:25 AM, Fredrik Noring wrote:
> The three-operand MULT and MULTU are the only R5900 specific
> instructions emitted by GCC 7.3. The R5900 also implements the three-
> operand MADD and MADDU instructions, but they are omitted in QEMU for
> now since they are absent in programs compiled by current GCC versions.

I'm not sure this GCC information is worthless in the commit message.

> Likewise, the R5900 specific pipeline 1 instruction variants MULT1,
> MULTU1, DIV1, DIVU1, MADD1, MADDU1, MFHI1, MFLO1, MTHI1 and MTLO1
> are omitted here as well.
> 
> Signed-off-by: Fredrik Noring <address@hidden>
> ---
>  target/mips/translate.c | 73 
> +++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 73 insertions(+)
> 
> diff --git a/target/mips/translate.c b/target/mips/translate.c
> index ab16cdb911..7e18ec0d03 100644
> --- a/target/mips/translate.c
> +++ b/target/mips/translate.c
> @@ -3768,6 +3768,77 @@ static void gen_muldiv(DisasContext *ctx, uint32_t opc,
>      tcg_temp_free(t1);
>  }
>  
> +/*
> + * These MULT and MULTU instructions implemented in for example the
> + * Toshiba/Sony R5900 and the Toshiba TX19, TX39 and TX79 core
> + * architectures are special three-operand variants with the syntax
> + *
> + *     MULT[U] rd, rs, rt
> + *
> + * such that
> + *
> + *     (rd, LO, HI) <- rs * rt
> + *
> + * where the low-order 32-bits of the result is placed into both the
> + * GPR rd and the special register LO. The high-order 32-bits of the
> + * result is placed into the special register HI.
> + *
> + * If the GPR rd is omitted in assembly language, it is taken to be 0,
> + * which is the zero register that always reads as 0.
> + */
> +static void gen_mul_txxx(DisasContext *ctx, uint32_t opc,
> +                         int acc, int rd, int rs, int rt)
> +{
> +    TCGv t0 = tcg_temp_new();
> +    TCGv t1 = tcg_temp_new();
> +
> +    gen_load_gpr(t0, rs);
> +    gen_load_gpr(t1, rt);
> +
> +    switch (opc) {
> +    case OPC_MULT:
> +        {
> +            TCGv_i32 t2 = tcg_temp_new_i32();
> +            TCGv_i32 t3 = tcg_temp_new_i32();
> +            tcg_gen_trunc_tl_i32(t2, t0);
> +            tcg_gen_trunc_tl_i32(t3, t1);
> +            tcg_gen_muls2_i32(t2, t3, t2, t3);
> +            if (rd) {
> +                tcg_gen_ext_i32_tl(cpu_gpr[rd], t2);
> +            }
> +            tcg_gen_ext_i32_tl(cpu_LO[acc], t2);
> +            tcg_gen_ext_i32_tl(cpu_HI[acc], t3);
> +            tcg_temp_free_i32(t2);
> +            tcg_temp_free_i32(t3);
> +        }
> +        break;
> +    case OPC_MULTU:
> +        {
> +            TCGv_i32 t2 = tcg_temp_new_i32();
> +            TCGv_i32 t3 = tcg_temp_new_i32();
> +            tcg_gen_trunc_tl_i32(t2, t0);
> +            tcg_gen_trunc_tl_i32(t3, t1);
> +            tcg_gen_mulu2_i32(t2, t3, t2, t3);
> +            if (rd) {
> +                tcg_gen_ext_i32_tl(cpu_gpr[rd], t2);
> +            }
> +            tcg_gen_ext_i32_tl(cpu_LO[acc], t2);
> +            tcg_gen_ext_i32_tl(cpu_HI[acc], t3);
> +            tcg_temp_free_i32(t2);
> +            tcg_temp_free_i32(t3);
> +        }
> +        break;
> +    default:
> +        MIPS_INVAL("mul R5900");

I'd use:

           MIPS_INVAL("mul/div Toshiba");

> +        generate_exception_end(ctx, EXCP_RI);
> +        goto out;
> +    }
> +
> + out:
> +    tcg_temp_free(t0);
> +    tcg_temp_free(t1);
> +}
> +
>  static void gen_mul_vr54xx (DisasContext *ctx, uint32_t opc,
>                              int rd, int rs, int rt)
>  {
> @@ -22378,6 +22449,8 @@ static void decode_opc_special_legacy(CPUMIPSState 
> *env, DisasContext *ctx)
>              check_insn(ctx, INSN_VR54XX);
>              op1 = MASK_MUL_VR54XX(ctx->opcode);
>              gen_mul_vr54xx(ctx, op1, rd, rs, rt);
> +        } else if (ctx->insn_flags & INSN_R5900) {
> +            gen_mul_txxx(ctx, op1, 0, rd, rs, rt);

Similarly, I'd name this gen_muldiv_txx9().

The code is correct, therefore:
Reviewed-by: Philippe Mathieu-Daudé <address@hidden>

Maybe the maintainer will agree to do these minor changes when taking
the patches.

>          } else {
>              gen_muldiv(ctx, op1, rd & 3, rs, rt);
>          }
>