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From: Richard Henderson <rth@twiddle.net>
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Date: Wed, 12 Aug 2015 10:49:21 -0700
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Subject: Re: [Qemu-devel] [PATCH for-2.5 24/30] m68k: add DBcc and Scc
 (memory operand)
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To: Laurent Vivier <laurent@vivier.eu>, qemu-devel@nongnu.org
Cc: peter.maydell@linaro.org, peter.crosthwaite@xilinx.com, Andreas Schwab <schwab@linux-m68k.org>, gerg@uclinux.org

On 08/09/2015 01:13 PM, Laurent Vivier wrote:
> +DISAS_INSN(scc_mem)
> +{
> +    TCGLabel *l1;
> +    int cond;
> +    TCGv dest;
> +
> +    l1 = gen_new_label();
> +    cond = (insn >> 8) & 0xf;
> +    dest = tcg_temp_local_new();
> +    tcg_gen_movi_i32(dest, 0);
> +    gen_jmpcc(s, cond ^ 1, l1);
> +    tcg_gen_movi_i32(dest, 0xff);
> +    gen_set_label(l1);
> +    DEST_EA(env, insn, OS_BYTE, dest, NULL);
> +    tcg_temp_free(dest);
> +}

It seems like this could just as easily be shared with scc?
DEST_EA handles a byte store into a register just fine.

I suppose the real ugliness at the moment is the tcg branch;
if you were using setcond instead that would help matters.
Adjusting the code surrounding gen_jmpcc is a larger task,
but it really would help a lot.  There are several examples
of how to organize such a thing...

> +DISAS_INSN(dbcc)
> +{
> +    TCGLabel *l1;
> +    TCGv reg;
> +    TCGv tmp;
> +    int16_t offset;
> +    uint32_t base;
> +
> +    reg = DREG(insn, 0);
> +    base = s->pc;
> +    offset = cpu_ldsw_code(env, s->pc);
> +    s->pc += 2;

read_im16?

> +    l1 = gen_new_label();
> +    gen_jmpcc(s, (insn >> 8) & 0xf, l1);
> +
> +    tmp = tcg_temp_new();
> +    tcg_gen_ext16s_i32(tmp, reg);
> +    tcg_gen_addi_i32(tmp, tmp, -1);
> +    gen_partset_reg(OS_WORD, reg, tmp);
> +    tcg_gen_brcondi_i32(TCG_COND_EQ, tmp, -1, l1);
> +    update_cc_op(s);
> +    gen_jmp_tb(s, 1, base + offset);
> +    gen_set_label(l1);
> +    update_cc_op(s);

Move the update_cc_op calls before the first branch.


r~