[clang] [Clang] Make the SizeType, SignedSizeType and PtrdiffType be named sugar types instead of built-in types (PR #143653)

[Matheus Izvekov via cfe-commits]

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@@ -14536,6 +14589,9 @@ static QualType getCommonSugarTypeNode(ASTContext &Ctx, const Type *X,
                                       DX->isCountInBytes(), DX->isOrNull(),
                                       CDX);
   }
+  case Type::PredefinedSugar: {
+    return QualType();
+  }
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mizvekov wrote:

If you had an underlying type that's non-canonical, then this should return a predefined type with an underlying type which is the common sugar between the two.

Since I suggested above to drop the underlying type, you should never hit here, and you can put this in the list of unreachable type classes.

https://github.com/llvm/llvm-project/pull/143653