[Flang] removing Float Bessel functions for AIX

[madanial]

Summary

AIX libc only provides bessel functions j0,j1,jn and y0,y1,yn but doesn't have their float equivalents j0f,j1f,jnf and y0f,y1f,ynf. These functions cause a build failure on AIX, taking them out results in a clean build.

[clementval]

What happen when you have code that requires these functions?

[madanial]

AIX was not on the target list for flang so it had to be added before answering your question. If those functions are required at compile time it results in a semantic error as these float bessel functions cannot be folded. If these functions are required at runtime it results in a undefined symbol linker error as it looks for jnf but cannot resolve it as it was taken out in order to be able to build.

[clementval]

Just add comment before merging.

flang/lib/Evaluate/intrinsics-library.cpp

298

Can you add a small comment so we remember why it's done.

[madanial]

Adding comment as requested

flang/lib/Evaluate/intrinsics-library.cpp

 //    bessel functions. However, they are not yet implemented in
 //    clang libc++ (ok in GNU libstdc++). Instead, the Posix libm
 //    extensions are used when available below.
 
 #if _POSIX_C_SOURCE >= 200112L || _XOPEN_SOURCE >= 600
 /// Define libm extensions
 /// Bessel functions are defined in POSIX.1-2001.
 
+// Remove float bessel funcitons for AIX as they are not supported
+#ifndef _AIX
 template <> struct HostRuntimeLibrary<float, LibraryVersion::LibmExtensions> {
   using F = FuncPointer<float, float>;
   using FN = FuncPointer<float, int, float>;
   static constexpr HostRuntimeFunction table[]{
       FolderFactory<F, F{::j0f}>::Create("bessel_j0"),
       FolderFactory<F, F{::j1f}>::Create("bessel_j1"),
       FolderFactory<FN, FN{::jnf}>::Create("bessel_jn"),
       FolderFactory<F, F{::y0f}>::Create("bessel_y0"),
       FolderFactory<F, F{::y1f}>::Create("bessel_y1"),
       FolderFactory<FN, FN{::ynf}>::Create("bessel_yn"),
   };
   static constexpr HostRuntimeMap map{table};
   static_assert(map.Verify(), "map must be sorted");
 };
+#endif
 
 template <> struct HostRuntimeLibrary<double, LibraryVersion::LibmExtensions> {
   using F = FuncPointer<double, double>;
   using FN = FuncPointer<double, int, double>;
   static constexpr HostRuntimeFunction table[]{
       FolderFactory<F, F{::j0}>::Create("bessel_j0"),
       FolderFactory<F, F{::j1}>::Create("bessel_j1"),
       FolderFactory<FN, FN{::jn}>::Create("bessel_jn"),