[clang] [llvm] [Clang][C++23] Core language changes from P1467R9 extended floating-point types and standard names. (PR #78503)

[Hubert Tong via llvm-commits]

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@@ -132,6 +133,70 @@ template <> struct llvm::DenseMapInfo<llvm::FoldingSetNodeID> {
     return LHS == RHS;
   }
 };
+constexpr unsigned CXX23FloatRankToIndex(clang::BuiltinType::Kind Kind) {
+  switch (Kind) {
+  case clang::BuiltinType::Float16:
+    return 0;
+  case clang::BuiltinType::BFloat16:
+    return 1;
+  case clang::BuiltinType::Float:
+    return 2;
+  case clang::BuiltinType::Double:
+    return 3;
+  case clang::BuiltinType::LongDouble:
+    return 4;
+  default:
+    // Both __float128 and __ibm128 are compiler extensions, not extended floating points.
+    // __float128 also predates the invention of floating-point types.
+    llvm_unreachable("Not a CXX23+ floating point builtin type");
----------------
hubert-reinterpretcast wrote:

Because `__float128` conflicts with `long double` in the name mangling (on at least some platforms), I would hesitate to call it an extended floating-point type. It's a non-conforming extension.

https://godbolt.org/z/98b696cr9

https://github.com/llvm/llvm-project/pull/78503