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

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Merged
merged 3 commits into from
Oct 18, 2024
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Fix build break in SemaHLSL.cpp on MSVC 2022: warning C4715: 'getResourceClass': not all control paths return a value #112767

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Fix build break in SemaHLSL.cpp on MSVC 2022: warning C4715: 'getReso…
dpaoliello Oct 17, 2024
7caa2a9
Update clang/lib/Sema/SemaHLSL.cpp
dpaoliello Oct 17, 2024
3271191
Update SemaHLSL.cpp
dpaoliello Oct 18, 2024
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1 change: 1 addition & 0 deletions clang/lib/Sema/SemaHLSL.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -102,6 +102,7 @@ static ResourceClass getResourceClass(RegisterType RT) {
return ResourceClass::Sampler;
case RegisterType::C:
case RegisterType::I:
default:
llvm_unreachable("unexpected RegisterType value");
}
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@mizvekov mizvekov Oct 17, 2024 •
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There is a very useful warning about switching on an enum where not all enumerators are covered.

Adding a default case suppresses this warning, but this is undesirable, as we want to see this warning pop up when we add a new enumerator.

Suggested change
default:
llvm_unreachable("unexpected RegisterType value");
}
llvm_unreachable("unexpected RegisterType value");
}
llvm_unreachable("unhandled RegisterType");

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@farzonl farzonl Oct 18, 2024 •
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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?

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.

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It sounds like line 107 will be impossible to hit.

Not impossible: someone can always cast an arbitrary value into the enum type, which is what MSVC is trying to guard against.

As a compromise we could keep the unreachable at the bottom, and then deliberately fall through to that in the unhandled cases:

  case RegisterType::C:
  case RegisterType::I:
    // Deliberately falling through to the unreachable below.
    break;
  }
  llvm_unreachable("unexpected RegisterType value");
}

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As a compromise we could keep the unreachable at the bottom, and then deliberately fall through to that in the unhandled cases:

FWIW, that's the usual approach we take.

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@farzonl farzonl Oct 18, 2024 •
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I'm fine with that. We do that in getRegisterType.

}
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