[clang] [HLSL] Finish exposing half types and intrinsics always (PR #132804)

[Sarah Spall via cfe-commits]

spall wrote:

> this is not NFC, so we should verify that we can call these intrinsics with `half` values even if 16-bit types aren't enabled, and that they properly codegen to 32-bit varia

> > > > > For example, for `abs`, it still depends on the _HLSL_16BIT_AVAILABILITY availability attribute. Does this PR intend to keep abs overloads using half "unexposed"? Or should that overload for abs be exposed too?
> > > > 
> > > > 
> > > > Oh I see what you are referring to. That might be my mistake; let me double check if I used the wrong __HLSL_AVAILABILITY
> > > 
> > > 
> > > Yeah, if the intention of this PR is to expose all half type overloads always, then I would think there is no more utility in defining `HLSL_16BIT_AVAILABILITY` anymore.
> > 
> > 
> > I think I was meant to use _HLSL_16BIT_AVAILABILITY and not _HLSL_AVAILABILITY; I'll fix that. Thanks for noticing the error!
> 
> What I'm trying to get at is, you're removing #ifdef __HLSL_ENABLE_16_BIT, and replacing it with an availability attribute making sure that the shader model is at least 6.2 for these functions. If you look at the definition for HLSL_16bit_availability, you'll notice that it's also defined under an ifdef: #ifdef __HLSL_ENABLE_16_BIT The essence of this PR seems to me like it's assuming from now on that #ifdef __HLSL_ENABLE_16_BIT will always be true. So, that means this availability attribute will always be defined. And it's identical to the HLSL_AVAILABILITY attribute. I might understand this incorrectly, but now it seems to me like there's no point or distinguishing use between HLSL_AVAILABILITY and HLSL_16bit_AVAILABILITY. Does that make sense? Which would imply that functions like `abs` should just use HLSL_Availability instead and we can do away with HLSL_16bit_AVAILABILITY. Since you want all function overloads with a half parameter to always be exposed.

@llvm-beanz  Thoughts on this?

https://github.com/llvm/llvm-project/pull/132804