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

[Joshua Cranmer via llvm-commits]

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@@ -7444,9 +7444,12 @@ isArithmeticArgumentPromotion(Sema &S, const ImplicitCastExpr *ICE) {
     From = VecTy->getElementType();
   if (const auto *VecTy = To->getAs<ExtVectorType>())
     To = VecTy->getElementType();
-  // It's a floating promotion if the source type is a lower rank.
-  return ICE->getCastKind() == CK_FloatingCast &&
-         S.Context.getFloatingTypeOrder(From, To) < 0;
+  // It's a floating promotion if the source type is float.
+  // [7.3.8p1][conv.fpprom] A prvalue of type float can be converted to a
+  // prvalue of type double. The value is unchanged.
+  return (ICE->getCastKind() == CK_FloatingCast &&
+          S.Context.isPromotableFloatingType(From) &&
+          S.Context.getPromotedFloatingType(From) == To);
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jcranmer-intel wrote:

Given that the *only* floating-point promotion is `float` -> `double`, and we've just seen C++23 add a slew of new types without any other promotions, I'm not sure these helper methods are helpful to understanding what's going on here, over just hard-coding the `float`->`double` check here.

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