[clang] Fix build break in SemaHLSL.cpp on MSVC 2022: warning C4715: 'getResourceClass': not all control paths return a value (PR #112767)

[Farzon Lotfi via cfe-commits]

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@@ -102,6 +102,7 @@ static ResourceClass getResourceClass(RegisterType RT) {
     return ResourceClass::Sampler;
   case RegisterType::C:
   case RegisterType::I:
+  default:
     llvm_unreachable("unexpected RegisterType value");
   }
----------------
farzonl wrote:

I don't agree with the suggested change of not using default.

@hekota  says:
> the switch covers all enum values. 

It sounds like  line 107 will be impossible to hit.

So then whats the difference between an unexpected and an unhandled register type? Why couldn't we have just done a default case?  Why can't MSVC2022 determine that all cases are covered? Are we really making a change to appease a false positive from a compiler warning?

If a new Register Type were added it would hit a llvm_unreachable on the default case and an implementer would quickly know to implement it from the call stack. I don't like the idea of changes to make a warning happy when that code change  adds undistinguishable terminology between unexpected and  unhandled. I would prefer not adding new terminology that would be confusing and instead add a default.





https://github.com/llvm/llvm-project/pull/112767