Re: [PATCH v4 32/47] target/ppc: Implement xxeval

[Richard Henderson]

On 2/22/22 04:36, matheus.ferst@eldorado.org.br wrote:
> +    tcg_gen_movi_i64(disj, 0);

The init here means there's one more OR generated than necessary.  Though perhaps it gets 
folded away...

> +
> +    /* Iterate over set bits from the least to the most significant bit */
> +    while (imm) {
> +        /*
> +         * Get the next bit to be processed with ctz64. Invert the result of
> +         * ctz64 to match the indexing used by PowerISA.
> +         */
> +        bit = 7 - ctz64(imm);
> +        if (bit & 0x4) {
> +            tcg_gen_mov_i64(conj, a);
> +        } else {
> +            tcg_gen_not_i64(conj, a);
> +        }
> +        if (bit & 0x2) {
> +            tcg_gen_and_i64(conj, conj, b);
> +        } else {
> +            tcg_gen_andc_i64(conj, conj, b);
> +        }
> +        if (bit & 0x1) {
> +            tcg_gen_and_i64(conj, conj, c);
> +        } else {
> +            tcg_gen_andc_i64(conj, conj, c);
> +        }
> +        tcg_gen_or_i64(disj, disj, conj);
> +
> +        /* Unset the least significant bit that is set */
> +        imm &= imm - 1;

I guess this works, though it's not nearly optimal.
It's certainly a good fallback for the out-of-line function.

Table 145 has the folded equivalent functions.  Implementing all 256 of them as is, twice, 
for both i64 and vec could be tedious.  But we could cherry-pick the easiest, or most 
commonly used, or something, and let all other imm values go through to out-of-line function.


r~