Index: llvm/lib/Support/Unix/Path.inc
===================================================================
--- llvm/lib/Support/Unix/Path.inc
+++ llvm/lib/Support/Unix/Path.inc
@@ -872,8 +872,13 @@

 void mapped_file_region::dontNeedImpl() {
   assert(Mode == mapped_file_region::readonly);
+#if defined(__MVS__) || defined(_AIX)
+  // If we don't have madvise, or it isn't beneficial, treat this as a no-op.
+  return;
+#else
   if (Mapping)
     ::madvise(Mapping, Size, MADV_DONTNEED);
+#endif
 }

 int mapped_file_region::alignment() {