HLSL offsetting

[Giovanni Mascellani]

Hi,

I finally managed to read through your messages, and it seems that we 
have a sort of agreement for trying with structured dereferences, which 
I agree with too.

Il 10/06/22 23:13, Zebediah Figura ha scritto:
>> On the other hand, the version of (b) I imagine changes hlsl_deref to:
>> ---
>> struct hlsl_deref
>> {
>>      struct hlsl_ir_var *var;
>>      unsigned int route_len;
>>      struct hlsl_src *route;
>> };
>> ---
>> Where route is intended to be a variable size array of component offsets. 
> 
> I was envisioning something more explicit, but this is simpler, so my 
> guess is that this is what we want.

I can live with Francisco's proposal, but my preference would be for 
something like:

enum hlsl_selector_type
{
     HLSL_SELECTOR_SUBSCRIPT,
     HLSL_SELECTOR_FIELD,
};

struct hlsl_selector
{
     enum hlsl_selector_type type;
     union
     {
         hlsl_src *subscript;
         unsigned int field;
     };
};

struct hlsl_deref
{
     struct hlsl_ir_var *var;
     unsigned int path_len;
     struct hlsl_selector *path;
};

This way field indices are kept as actual numbers, not other nodes that 
have to resolve to a constant uint value. In general I like data types 
to constrain as much as possible to the valid values that you can store 
in them (and I don't think there is any way in HLSL to make a dynamic 
reference to a field of a structure, like it is possible in C++).

Giovanni.