[v2 PATCH vkd3d 2/4] vkd3d-shader/hlsl: Cast round() input to float.

[Zebediah Figura (she/her)]

On 1/20/22 06:12, Matteo Bruni wrote:
> On Thu, Jan 20, 2022 at 12:42 AM Zebediah Figura (she/her)
> <zfigura at codeweavers.com> wrote:
>>
>> On 1/19/22 06:03, Matteo Bruni wrote:
>>> On Mon, Dec 20, 2021 at 10:44 PM Zebediah Figura (she/her)
>>> <zfigura at codeweavers.com> wrote:
>>>>
>>>> On 12/20/21 12:15, Zebediah Figura (she/her) wrote:
>>>>> On 12/19/21 06:41, Nikolay Sivov wrote:
>>>>>> +static struct hlsl_ir_node *intrinsic_float_convert_arg(struct
>>>>>> hlsl_ctx *ctx,
>>>>>> +        const struct parse_initializer *params, struct hlsl_ir_node
>>>>>> *arg, const struct vkd3d_shader_location *loc)
>>>>>> +{
>>>>>> +    struct hlsl_type *type = arg->data_type;
>>>>>> +
>>>>>> +    if (type->base_type == HLSL_TYPE_FLOAT || type->base_type ==
>>>>>> HLSL_TYPE_HALF)
>>>>>> +        return arg;
>>>>>
>>>>> add_implicit_conversion() already does this.
>>>>
>>>> Sorry, turns out I'm wrong; this preserves the input type for half,
>>>> whereas add_implicit_conversion() alone would not.
>>>
>>> I wonder if that's what it should do in the first place?
>>
>> Yes, witness the following shader:
>>
>> ---
>>
>> uint func(float x) { return 1; }
>> uint func(half x) { return 2; }
>>
>> float4 main(void) : sv_target
>> {
>>       return float4(func(float(0)), func(half(0)), func(int(0)),
>> func(uint(0)));
>> }
>>
>> ---
>>
>> Native reduces this to (1, 2, 1, 1).
> 
> Fun... But at least it means we can fix add_implicit_conversion() and
> avoid that kind of workarounds, if I understand correctly.

I... guess, but it seems janky. The main point of 
add_implicit_conversion() is for stuff like assignment RHS or return 
values. If we had add_implicit_conversion() pass through half it'd 
generate IR like

2:  half | 1.0
3:       | x = @2
4: float | x


(i.e. "x" is a float variable). Which... works, I guess? Maybe it's not 
that bad, since we already do a somewhat similar thing for scalar vs vec1.