[PATCH vkd3d 3/6] vkd3d-shader/hlsl: Lower scalar-to-vector casts to swizzles.

[Giovanni Mascellani]

Signed-off-by: Giovanni Mascellani <gmascellani at codeweavers.com>

On 23/11/21 02:45, Zebediah Figura wrote:
> +/* Lower casts from vec1 to vecN to swizzles. */
> +static bool lower_broadcasts(struct hlsl_ctx *ctx, struct hlsl_ir_node *instr, void *context)
> +{
> +    const struct hlsl_type *src_type, *dst_type;
> +    struct hlsl_ir_expr *cast;
> +
> +    if (instr->type != HLSL_IR_EXPR)
> +        return false;
> +    cast = hlsl_ir_expr(instr);
> +    src_type = cast->operands[0].node->data_type;
> +    dst_type = cast->node.data_type;
> +
> +    if (cast->op == HLSL_OP1_CAST
> +            && src_type->type <= HLSL_CLASS_VECTOR && dst_type->type <= HLSL_CLASS_VECTOR
> +            && src_type->dimx == 1)
> +    {
> +        struct hlsl_ir_swizzle *swizzle;
> +
> +        if (!(swizzle = hlsl_new_swizzle(ctx, HLSL_SWIZZLE(X, X, X, X), dst_type->dimx, &cast->node, &cast->node.loc)))
> +            return false;
> +        list_add_after(&cast->node.entry, &swizzle->node.entry);
> +
> +        cast->node.data_type = hlsl_get_scalar_type(ctx, dst_type->base_type);
> +        replace_node(&cast->node, &swizzle->node);
> +        hlsl_src_remove(&swizzle->val);
> +        hlsl_src_from_node(&swizzle->val, &cast->node);

I guess this answers to the question in my previous email (WRT why you 
want replace_node to not delete the replaced node).

This solution seems correct, but I cannot refrain from thinking the code 
would be more readable if you just created a new cast and just removed 
(and possibly deleted, but that's not very relevant) the old one.

While I am all for avoiding useless allocation round trips, I don't 
think that doing so at the expense of code readability is a good idea, 
until it is shown that that allocation really is a performance bottleneck.

Thanks, Giovanni.