[llvm] [APFloat]extract `fltSemantics::isRepresentableBy` to header (PR #122636)

[Congcong Cai via llvm-commits]

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@@ -281,6 +281,11 @@ struct APFloatBase {
   /// anything real.
   static const fltSemantics &Bogus() LLVM_READNONE;
 
+  // Returns true if any number described by this semantics can be precisely
+  // represented by the specified semantics. Does not take into account
+  // the value of fltNonfiniteBehavior.
+  static bool isRepresentableBy(const fltSemantics &A, const fltSemantics &B);
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HerrCai0907 wrote:

For the usecase of this functions. I want to warn for implicit loss of accuracy when floating point conversation happened in compiler frontend type systems.
It needs API to detect floating point type compatibility.

https://github.com/llvm/llvm-project/pull/122636