[flang] Use libm routine for compile-time folding on AIX

flang/lib/Evaluate/CMakeLists.txt

@@ -58,6 +58,7 @@ add_flang_library(FortranEvaluate
   tools.cpp
   type.cpp
   variable.cpp
+  wrappers.c
 
   LINK_LIBS
   FortranCommon

flang/lib/Evaluate/intrinsics-library.cpp

@@ -277,6 +277,32 @@ static std::complex<HostT> StdPowF2B(
   return std::pow(x, y);
 }
 
+#ifdef _AIX
+extern "C" {
+void csqrtf_wrapper(const float[], float[]);
+void csqrt_wrapper(const double[], double[]);
+} // extern "C"
+#endif
+
+template <typename HostT>
+static std::complex<HostT> CSqrt(const std::complex<HostT> &x) {
+  std::complex<HostT> res;
+#if _AIX
+  HostT y[2]{x.real(), x.imag()};
+  HostT r[2];
+  if constexpr (std::is_same_v<HostT, float>) {
+    csqrtf_wrapper(y, r);
+  } else if constexpr (std::is_same_v<HostT, double>) {
+    csqrt_wrapper(y, r);
+  }
+  res.real(r[0]);
+  res.imag(r[1]);
+#else
+  res = std::sqrt(x);
+#endif
+  return res;
+}
+
 template <typename HostT>
 struct HostRuntimeLibrary<std::complex<HostT>, LibraryVersion::Libm> {
   using F = FuncPointer<std::complex<HostT>, const std::complex<HostT> &>;
@@ -302,7 +328,7 @@ struct HostRuntimeLibrary<std::complex<HostT>, LibraryVersion::Libm> {
       FolderFactory<F2B, F2B{StdPowF2B}>::Create("pow"),
       FolderFactory<F, F{std::sin}>::Create("sin"),
       FolderFactory<F, F{std::sinh}>::Create("sinh"),
-      FolderFactory<F, F{std::sqrt}>::Create("sqrt"),
+      FolderFactory<F, F{CSqrt}>::Create("sqrt"),
       FolderFactory<F, F{std::tan}>::Create("tan"),
       FolderFactory<F, F{std::tanh}>::Create("tanh"),
   };

flang/lib/Evaluate/wrappers.c

@@ -0,0 +1,25 @@
+//===-- lib/Evaluate/wrappers.c -------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifdef _AIX
+#include <complex.h>
+
+void csqrtf_wrapper(const float x[2], float res[2]) {
+  float complex c = x[0] + I * x[1];
+  float complex r = csqrtf(c);
+  res[0] = crealf(r);
+  res[1] = cimagf(r);
+}
+
+void csqrt_wrapper(const double x[2], double res[2]) {
+  double complex c = x[0] + I * x[1];
+  double complex r = csqrt(c);
+  res[0] = creal(r);
+  res[1] = cimag(r);
+}
+#endif