[Mesa-dev] [PATCH] tgsi: document and fixup IF and BREAKC instrunctions

[Jose Fonseca]

----- Original Message -----
> ----- Original Message -----
> > Ah.. This indeed rings a bell. I don't recall the details but I'm pretty
> > sure
> > I was against dual semantics. And the fact that this problem is again
> > showing its ugly head is the proof of it.
> > 
> > We really should have two IF opcodes. And the state tracker should choose
> > which one it wants.
> 
> What would be the difference between those two opcodes though? 

> The current IF
> does a bitwise comparison, 

No, according to Marek, the current IF code has two possible behaviors:
- a float comparison for drivers which do not support native integers (i915)
- a bit comparison for drivers which support native integers (others)

This would be the different for both opcodes. We could call the former FIF or just IF, and the later UIF.

> so would we add another opcode that does exactly
> the same thing and say that the first one can be emulated with float
> comparisons? 

> I'm not sure if that helps. I guess we could change the first
> one and make that one compare floats, then introduce another one that does
> what IF currently is doing, but that seems weird as well. 

> Why not just say
> that if your hardware can't do bitwise comparisons, just keep emulating them
> with floats? That seems easier and it preserves the current behavior for
> everyone.

That's the point. Hardware can't do bitwise comparisons, and we need to emulate with floats, and for that we need a IF with float argument.

And we need a IF with bitwise arguments for the rest.

I really don't like the semantic of an opcode to depend on the hard capabilities.

Jose