Re: [PATCH 15/30] tcg/loongarch: Implement clz/ctz ops

[Richard Henderson]

On 9/20/21 1:04 AM, WANG Xuerui wrote:
> +static void tcg_out_clzctz(TCGContext *s, LoongArchInsn opc,
> +                           TCGReg a0, TCGReg a1, TCGReg a2)
> +{
> +    /* all clz/ctz insns belong to DJ-format */
> +    tcg_out32(s, encode_dj_insn(opc, TCG_REG_TMP0, a1));
> +    /* a0 = a1 ? REG_TMP0 : a2 */
> +    tcg_out_opc_maskeqz(s, TCG_REG_TMP0, TCG_REG_TMP0, a1);
> +    tcg_out_opc_masknez(s, a0, a2, a1);
> +    tcg_out_opc_or(s, a0, TCG_REG_TMP0, a0);
> +}

From Song Gao's translation, I believe that ctz(0) == 32 or 64, depending on the 
operation width.  This is in fact the most common result, so it's worth specializing.  See 
tcg/i386/tcg-target.c.inc, tcg_out_clz, have_lzcnt.

But what's here looks ok.
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>


r~