Re: [Qemu-devel] [RFC v1 09/13] target-ppc: add cmpeqb instruction

[David Gibson <david@gibson.dropbear.id.au>]

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On Mon, Jul 18, 2016 at 10:35:13PM +0530, Nikunj A Dadhania wrote:
> From: Swapnil Bokade <bokadeswapnil@gmail.com>
> 
> Search a byte in the stream of 8bytes provided in the register
> 
> Signed-off-by: Sandipan Das <sandipandas1990@gmail.com>
> [ Modified the logic to use lesser temporaries ]
> Signed-off-by: Nikunj A Dadhania <nikunj@linux.vnet.ibm.com>

rth's reference may obsolete the suggestions below.

> ---
>  target-ppc/translate.c | 27 +++++++++++++++++++++++++++
>  1 file changed, 27 insertions(+)
> 
> diff --git a/target-ppc/translate.c b/target-ppc/translate.c
> index a57f7dd..8f7ff49 100644
> --- a/target-ppc/translate.c
> +++ b/target-ppc/translate.c
> @@ -856,6 +856,32 @@ static void gen_cmprb(DisasContext *ctx)
>      tcg_temp_free(src2hi);
>  }
>  
> +/* cmpeqb */
> +static void gen_cmpeqb(DisasContext *ctx)
> +{
> +    TCGLabel *l1 = gen_new_label();
> +    TCGLabel *l2 = gen_new_label();
> +    TCGv src1 = tcg_temp_local_new();
> +    TCGv t0 = tcg_temp_local_new();
> +    TCGv arg1 = cpu_gpr[rB(ctx->opcode)];
> +    int i;
> +
> +    tcg_gen_andi_tl(src1, cpu_gpr[rA(ctx->opcode)], 0xFF);
> +    for (i = 0; i < 64; i += 8) {
> +        tcg_gen_shri_tl(t0, arg1, i);
> +        tcg_gen_andi_tl(t0, t0, 0xFF);

Shifting direct from the original arg each time seems awkward when you
can just shift a working reg by 8 bits each loop.  I suspect that
could save you a temporary.

> +        tcg_gen_brcond_tl(TCG_COND_EQ, src1, t0, l1);
> +    }
> +    tcg_gen_movi_i32(cpu_crf[crfD(ctx->opcode)], 0);
> +    tcg_gen_br(l2);
> +    gen_set_label(l1);
> +    /* Set match bit, i.e. CRF_GT */
> +    tcg_gen_movi_i32(cpu_crf[crfD(ctx->opcode)], 1 << CRF_GT);
> +    gen_set_label(l2);

You should only need one branch at most, either by initializing the
CRF first, or by moving a variable to it.

> +    tcg_temp_free(src1);
> +    tcg_temp_free(t0);
> +}
> +
>  /* isel (PowerPC 2.03 specification) */
>  static void gen_isel(DisasContext *ctx)
>  {
> @@ -10040,6 +10066,7 @@ GEN_HANDLER(cmp, 0x1F, 0x00, 0x00, 0x00400000, PPC_INTEGER),
>  GEN_HANDLER(cmpi, 0x0B, 0xFF, 0xFF, 0x00400000, PPC_INTEGER),
>  GEN_HANDLER(cmpl, 0x1F, 0x00, 0x01, 0x00400000, PPC_INTEGER),
>  GEN_HANDLER(cmpli, 0x0A, 0xFF, 0xFF, 0x00400000, PPC_INTEGER),
> +GEN_HANDLER_E(cmpeqb, 0x1F, 0x00, 0x07, 0x00600000, PPC_NONE, PPC2_ISA300),
>  GEN_HANDLER_E(cmpb, 0x1F, 0x1C, 0x0F, 0x00000001, PPC_NONE, PPC2_ISA205),
>  GEN_HANDLER_E(cmprb, 0x1F, 0x00, 0x06, 0x00400001, PPC_NONE, PPC2_ISA300),
>  GEN_HANDLER(isel, 0x1F, 0x0F, 0xFF, 0x00000001, PPC_ISEL),

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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