diff --git a/llvm/cmake/config-ix.cmake b/llvm/cmake/config-ix.cmake
--- a/llvm/cmake/config-ix.cmake
+++ b/llvm/cmake/config-ix.cmake
@@ -243,7 +243,6 @@
 check_symbol_exists(isatty unistd.h HAVE_ISATTY)
 check_symbol_exists(futimens sys/stat.h HAVE_FUTIMENS)
 check_symbol_exists(futimes sys/time.h HAVE_FUTIMES)
-check_symbol_exists(posix_fallocate fcntl.h HAVE_POSIX_FALLOCATE)
 # AddressSanitizer conflicts with lib/Support/Unix/Signals.inc
 # Avoid sigaltstack on Apple platforms, where backtrace() cannot handle it
 # (rdar://7089625) and _Unwind_Backtrace is unusable because it cannot unwind
diff --git a/llvm/include/llvm/Config/config.h.cmake b/llvm/include/llvm/Config/config.h.cmake
--- a/llvm/include/llvm/Config/config.h.cmake
+++ b/llvm/include/llvm/Config/config.h.cmake
@@ -152,9 +152,6 @@
 /* Define to 1 if you have the `malloc_zone_statistics' function. */
 #cmakedefine HAVE_MALLOC_ZONE_STATISTICS ${HAVE_MALLOC_ZONE_STATISTICS}
 
-/* Define to 1 if you have the `posix_fallocate' function. */
-#cmakedefine HAVE_POSIX_FALLOCATE ${HAVE_POSIX_FALLOCATE}
-
 /* Define to 1 if you have the `posix_spawn' function. */
 #cmakedefine HAVE_POSIX_SPAWN ${HAVE_POSIX_SPAWN}
 
diff --git a/llvm/lib/Support/Unix/Path.inc b/llvm/lib/Support/Unix/Path.inc
--- a/llvm/lib/Support/Unix/Path.inc
+++ b/llvm/lib/Support/Unix/Path.inc
@@ -590,19 +590,6 @@
 }
 
 std::error_code resize_file(int FD, uint64_t Size) {
-#if defined(HAVE_POSIX_FALLOCATE)
-  // If we have posix_fallocate use it. Unlike ftruncate it always allocates
-  // space, so we get an error if the disk is full.
-  if (int Err = ::posix_fallocate(FD, 0, Size)) {
-#ifdef _AIX
-    constexpr int NotSupportedError = ENOTSUP;
-#else
-    constexpr int NotSupportedError = EOPNOTSUPP;
-#endif
-    if (Err != EINVAL && Err != NotSupportedError)
-      return std::error_code(Err, std::generic_category());
-  }
-#endif
   // Use ftruncate as a fallback. It may or may not allocate space. At least on
   // OS X with HFS+ it does.
   if (::ftruncate(FD, Size) == -1)
diff --git a/llvm/utils/gn/secondary/llvm/include/llvm/Config/BUILD.gn b/llvm/utils/gn/secondary/llvm/include/llvm/Config/BUILD.gn
--- a/llvm/utils/gn/secondary/llvm/include/llvm/Config/BUILD.gn
+++ b/llvm/utils/gn/secondary/llvm/include/llvm/Config/BUILD.gn
@@ -143,7 +143,6 @@
       "HAVE_LINK_H=1",
       "HAVE_LSEEK64=1",
       "HAVE_MALLINFO=1",
-      "HAVE_POSIX_FALLOCATE=1",
       "HAVE_STRUCT_STAT_ST_MTIM_TV_NSEC=1",
     ]
   } else {
@@ -152,7 +151,6 @@
       "HAVE_LINK_H=",
       "HAVE_LSEEK64=",
       "HAVE_MALLINFO=",
-      "HAVE_POSIX_FALLOCATE=",
       "HAVE_STRUCT_STAT_ST_MTIM_TV_NSEC=",
     ]
   }
diff --git a/utils/bazel/llvm-project-overlay/llvm/config.bzl b/utils/bazel/llvm-project-overlay/llvm/config.bzl
--- a/utils/bazel/llvm-project-overlay/llvm/config.bzl
+++ b/utils/bazel/llvm-project-overlay/llvm/config.bzl
@@ -43,7 +43,6 @@
     "HAVE_LINK_H=1",
     "HAVE_LSEEK64=1",
     "HAVE_MALLINFO=1",
-    "HAVE_POSIX_FALLOCATE=1",
     "HAVE_SBRK=1",
     "HAVE_STRUCT_STAT_ST_MTIM_TV_NSEC=1",
 ]
diff --git a/utils/bazel/llvm-project-overlay/llvm/include/llvm/Config/config.h b/utils/bazel/llvm-project-overlay/llvm/include/llvm/Config/config.h
--- a/utils/bazel/llvm-project-overlay/llvm/include/llvm/Config/config.h
+++ b/utils/bazel/llvm-project-overlay/llvm/include/llvm/Config/config.h
@@ -165,9 +165,6 @@
 /* Define to 1 if you have the `malloc_zone_statistics' function. */
 /* HAVE_MALLOC_ZONE_STATISTICS defined in Bazel */
 
-/* Define to 1 if you have the `posix_fallocate' function. */
-/* HAVE_POSIX_FALLOCATE defined in Bazel */
-
 /* Define to 1 if you have the `posix_spawn' function. */
 #define HAVE_POSIX_SPAWN 1
 
diff --git a/utils/bazel/llvm_configs/config.h.cmake b/utils/bazel/llvm_configs/config.h.cmake
--- a/utils/bazel/llvm_configs/config.h.cmake
+++ b/utils/bazel/llvm_configs/config.h.cmake
@@ -152,9 +152,6 @@
 /* Define to 1 if you have the `malloc_zone_statistics' function. */
 #cmakedefine HAVE_MALLOC_ZONE_STATISTICS ${HAVE_MALLOC_ZONE_STATISTICS}
 
-/* Define to 1 if you have the `posix_fallocate' function. */
-#cmakedefine HAVE_POSIX_FALLOCATE ${HAVE_POSIX_FALLOCATE}
-
 /* Define to 1 if you have the `posix_spawn' function. */
 #cmakedefine HAVE_POSIX_SPAWN ${HAVE_POSIX_SPAWN}