[clang] [HLSL] Add validation for the -enable-16bit-types option (PR #85340)

[Damyan Pepper via cfe-commits]

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@@ -4258,6 +4258,18 @@ bool CompilerInvocation::ParseLangArgs(LangOptions &Opts, ArgList &Args,
       } else {
         llvm_unreachable("expected DXIL or SPIR-V target");
       }
+      // validate that if fnative-half-type is given, that
+      // the language standard is at least hlsl2021, and that
+      // the target shader model is at least 6.2
+      if (Args.getLastArg(OPT_fnative_half_type)) {
+        bool LangStdArgIsValid = Opts.LangStd >= LangStandard::lang_hlsl2021;
+        bool TPArgIsValid = T.getOSVersion() >= VersionTuple(6, 2);
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damyanp wrote:

What does the `TP` prefix mean in this context?

nits on the naming here: neither of these bools really indicate if these arguments are "valid".  The first one is "IsAtLeastHLSL2021" and the second is "IsAtLeastShaderModel62".  It may even be clearer just to inline these into the if condition.

https://github.com/llvm/llvm-project/pull/85340