Re: [PATCH v3 10/11] Hexagon (target/hexagon) Use direct block chaining for direct jump/branch

[Richard Henderson <richard.henderson@linaro.org>]

On 11/5/22 06:26, Taylor Simpson wrote:
> Direct block chaining is documented here
> https://qemu.readthedocs.io/en/latest/devel/tcg.html#direct-block-chaining
> 
> Recall that Hexagon allows packets with multiple jumps where only the first
> one with a true predicate will actually jump.  So, we can only use direct
> block chaining when the packet contains a single PC-relative jump.

Not quite accurate.

Only the first two direct branches can use direct block chaining.  Other exits from the 
translation block could use indirect block chaining (tcg_gen_lookup_and_goto_ptr).  You 
just have to remember which is taken.

That said, this is certainly an improvement.

> +    if (ctx->pkt->pkt_has_multi_cof) {
> +        gen_write_new_pc_addr(ctx, tcg_constant_tl(dest), pred);
> +    } else {
> +        /* Defer this jump to the end of the TB */
> +        g_assert(ctx->branch_cond == NULL);
> +        ctx->has_single_direct_branch = true;
> +        if (pred != NULL) {
> +            ctx->branch_cond = tcg_temp_local_new();
> +            tcg_gen_mov_tl(ctx->branch_cond, pred);
> +        }
> +        ctx->branch_dest = dest;

Perhaps re-use hex_branch_taken as branch_cond?

Anyway,
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>


r~