[PATCH] D124790: [HLSL] Enable half type for hlsl.

[Xiang Li via Phabricator via cfe-commits]

python3kgae added inline comments.


================
Comment at: clang/lib/Basic/LangOptions.cpp:197
 
-  // OpenCL has half keyword
-  Opts.Half = Opts.OpenCL;
+  // OpenCL and HLSL have half keyword
+  Opts.Half = Opts.OpenCL || Opts.HLSL;
----------------
python3kgae wrote:
> aaron.ballman wrote:
> > python3kgae wrote:
> > > aaron.ballman wrote:
> > > > Shouldn't this be looking for HLSL 2018? Or shader model 6.2?
> > > half keyword is always available.
> > > Without enable_16bit_types, half will be like using half=float.
> > > With enable_16bit_types, half will be real half.
> > > 
> > > The check for HLSL 2018 and shader model 6.2 will be in another PR, still WIP. I'll add FIXME about it.
> > > half keyword is always available.
> > > Without enable_16bit_types, half will be like using half=float.
> > > With enable_16bit_types, half will be real half.
> > 
> > Is there room for change here, or is this strictly required by HLSL? This strikes me as just begging to confuse users into creating ODR violations. CC @beanz 
> Here's the doc about half for dxc.
> https://github.com/microsoft/DirectXShaderCompiler/wiki/16-Bit-Scalar-Types
> 
> Old doc for fxc (the old shader compiler for shader model <= 5.1) is here
> https://docs.microsoft.com/en-us/windows/win32/direct3dhlsl/dx-graphics-hlsl-scalar
> 
> Change the behavior might affect a lot of existing shaders.
More detail about half from https://github.com/tex3d.

half originally mapped to a fuzzy "partial precision" float, where some operations were designated as _pp, meaning the implementation was free to use lower-precision math for those operations (like 24-bit, but not specified for the language). All storage in host-visible memory would still be float. "partial precision" went away with DX9, eventually to be replaced with min-precision with a specific minimum precision an implementation was allowed to use. When "partial precision" went away, it simply mapped to float for DX10+.
People could have tried to use it liberally when they thought 32-bit precision wasn't necessary, without explicitly targeting/testing API/hardware that actually supported lower precision.


Repository:
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  https://reviews.llvm.org/D124790/new/

https://reviews.llvm.org/D124790