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

[Zahira Ammarguellat via cfe-commits]

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@@ -112,6 +112,85 @@ enum FloatingRank {
   Ibm128Rank
 };
 
+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");
+  }
+}
+
+// C++23 6.8.6p2 [conv.rank]
+// Grid to determine the rank of a floating point type when compared with
+// another floating point type.
+constexpr std::array<std::array<FloatConvRankCompareResult, 5>, 5>
+    CXX23FloatingPointConversionRankMap = {
+        {// Float16 x Float16
+         // Float16 x BFloat16
+         // Float16 x Float
+         // Float16 x Double
+         // Float16 x LongDouble
+         {{FloatConvRankCompareResult::FRCR_Equal,
+           FloatConvRankCompareResult::FRCR_Unordered,
+           FloatConvRankCompareResult::FRCR_Lesser,
+           FloatConvRankCompareResult::FRCR_Lesser,
+           FloatConvRankCompareResult::FRCR_Lesser}},
+
+         // BFloat16 x Float16
+         // BFloat16 x BFloat16
+         // BFloat16 x Float
+         // BFloat16 x Double
+         // BFloat16 x LongDouble
+         {{FloatConvRankCompareResult::FRCR_Unordered,
+           FloatConvRankCompareResult::FRCR_Equal,
+           FloatConvRankCompareResult::FRCR_Lesser,
+           FloatConvRankCompareResult::FRCR_Lesser,
+           FloatConvRankCompareResult::FRCR_Lesser}},
+
+         // Float x Float16
+         // Float x BFloat16
+         // Float x Float
+         // Float x Double
+         // Float x LongDouble
+         {{FloatConvRankCompareResult::FRCR_Greater,
+           FloatConvRankCompareResult::FRCR_Greater,
+           FloatConvRankCompareResult::FRCR_Equal,
+           FloatConvRankCompareResult::FRCR_Lesser,
+           FloatConvRankCompareResult::FRCR_Lesser}},
+
+         // Double x Float16
+         // Double x BFloat16
+         // Double x Float
+         // Double x Double
+         // Double x LongDouble
+         {{FloatConvRankCompareResult::FRCR_Greater,
+           FloatConvRankCompareResult::FRCR_Greater,
+           FloatConvRankCompareResult::FRCR_Greater,
+           FloatConvRankCompareResult::FRCR_Equal,
+           FloatConvRankCompareResult::FRCR_Lesser}},
+
+         // LongDouble x Float16
+         // LongDouble x BFloat16
+         // LongDouble x Float
+         // LongDouble x Double
+         // LongDouble x LongDouble
+         {{FloatConvRankCompareResult::FRCR_Greater,
+           FloatConvRankCompareResult::FRCR_Greater,
+           FloatConvRankCompareResult::FRCR_Greater,
+           FloatConvRankCompareResult::FRCR_Greater,
+           FloatConvRankCompareResult::FRCR_Equal}}}};
+
----------------
zahiraam wrote:

Shouldn't we have cases here where we generate FRCR_Equal_Lesser_Subrank or FRCR_Equal_Greater_Subrank?

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