[Flang] Add __powerpc__ macro to set c_intmax_t to c_int64_t rather than c_int128_t as PowerPC only supports up to c_int64_t. (#81222)

PowerPC only supports up to `c_int64_t`. Add macro `__powerpc__` and
preprocess it for setting `c_intmax_t` in `iso_c_binding` intrinsic
module.

Author: DanielCChen

flang/lib/Frontend/CompilerInvocation.cpp

@@ -1326,10 +1326,23 @@ void CompilerInvocation::setDefaultPredefinitions() {
     Fortran::common::setOpenMPMacro(getLangOpts().OpenMPVersion,
                                     fortranOptions.predefinitions);
   }
+
   llvm::Triple targetTriple{llvm::Triple(this->targetOpts.triple)};
-  if (targetTriple.getArch() == llvm::Triple::ArchType::x86_64) {
+  switch (targetTriple.getArch()) {
+  default:
+    break;
+  case llvm::Triple::ArchType::x86_64:
     fortranOptions.predefinitions.emplace_back("__x86_64__", "1");
     fortranOptions.predefinitions.emplace_back("__x86_64", "1");
+    break;
+  case llvm::Triple::ArchType::ppc:
+  case llvm::Triple::ArchType::ppcle:
+  case llvm::Triple::ArchType::ppc64:
+  case llvm::Triple::ArchType::ppc64le:
+    // '__powerpc__' is a generic macro for any PowerPC cases. e.g. Max integer
+    // size.
+    fortranOptions.predefinitions.emplace_back("__powerpc__", "1");
+    break;
   }
 }
 

flang/module/iso_c_binding.f90

@@ -47,7 +47,11 @@ module iso_c_binding
     c_long_long = c_int64_t, &
     c_signed_char = c_int8_t, &
     c_size_t = kind(c_sizeof(1)), &
+#if __powerpc__
+    c_intmax_t = c_int64_t, &
+#else
     c_intmax_t = c_int128_t, &
+#endif
     c_intptr_t = c_size_t, &
     c_ptrdiff_t = c_size_t
   integer, parameter, public :: &

flang/test/Driver/predefined-macros-powerpc.f90

@@ -0,0 +1,11 @@
+! Test predefined macro for PowerPC architecture
+
+! RUN: %flang_fc1 -cpp -E %s | FileCheck %s
+! REQUIRES: target=powerpc{{.*}}
+
+! CHECK: integer :: var1 = 1
+
+#if __powerpc__
+  integer :: var1 = __powerpc__
+#endif
+end program