Index: lib/profile/InstrProfData.inc
===================================================================
--- lib/profile/InstrProfData.inc
+++ lib/profile/InstrProfData.inc
@@ -265,6 +265,9 @@
 INSTR_PROF_SECT_ENTRY(IPSK_covmap, \
                       INSTR_PROF_QUOTE(INSTR_PROF_COVMAP_COMMON), \
                       INSTR_PROF_COVMAP_COFF, "__LLVM_COV,")
+INSTR_PROF_SECT_ENTRY(IPSK_orderfile, \
+                      INSTR_PROF_QUOTE(INSTR_PROF_ORDERFILE_COMMON), \
+                      INSTR_PROF_QUOTE(INSTR_PROF_ORDERFILE_COFF), "__DATA,")
 
 #undef INSTR_PROF_SECT_ENTRY
 #endif
@@ -656,6 +659,7 @@
 #define INSTR_PROF_VALS_COMMON __llvm_prf_vals
 #define INSTR_PROF_VNODES_COMMON __llvm_prf_vnds
 #define INSTR_PROF_COVMAP_COMMON __llvm_covmap
+#define INSTR_PROF_ORDERFILE_COMMON __llvm_orderfile
 /* Windows section names. Because these section names contain dollar characters,
  * they must be quoted.
  */
@@ -665,6 +669,7 @@
 #define INSTR_PROF_VALS_COFF ".lprfv$M"
 #define INSTR_PROF_VNODES_COFF ".lprfnd$M"
 #define INSTR_PROF_COVMAP_COFF ".lcovmap$M"
+#define INSTR_PROF_ORDERFILE_COFF ".lorderfile$M"
 
 #ifdef _WIN32
 /* Runtime section names and name strings.  */
@@ -678,6 +683,7 @@
 /* Value profile nodes section. */
 #define INSTR_PROF_VNODES_SECT_NAME INSTR_PROF_VNODES_COFF
 #define INSTR_PROF_COVMAP_SECT_NAME INSTR_PROF_COVMAP_COFF
+#define INSTR_PROF_ORDERFILE_SECT_NAME INSTR_PROF_ORDERFILE_COFF
 #else
 /* Runtime section names and name strings.  */
 #define INSTR_PROF_DATA_SECT_NAME INSTR_PROF_QUOTE(INSTR_PROF_DATA_COMMON)
@@ -690,8 +696,18 @@
 /* Value profile nodes section. */
 #define INSTR_PROF_VNODES_SECT_NAME INSTR_PROF_QUOTE(INSTR_PROF_VNODES_COMMON)
 #define INSTR_PROF_COVMAP_SECT_NAME INSTR_PROF_QUOTE(INSTR_PROF_COVMAP_COMMON)
+/* Order file instrumentation. */
+#define INSTR_PROF_ORDERFILE_SECT_NAME                                         \
+  INSTR_PROF_QUOTE(INSTR_PROF_ORDERFILE_COMMON)
 #endif
 
+#define INSTR_PROF_ORDERFILE_BUFFER_NAME _llvm_order_file_buffer
+#define INSTR_PROF_ORDERFILE_BUFFER_NAME_STR                                   \
+  INSTR_PROF_QUOTE(INSTR_PROF_ORDERFILE_BUFFER_NAME)
+#define INSTR_PROF_ORDERFILE_BUFFER_IDX_NAME _llvm_order_file_buffer_idx
+#define INSTR_PROF_ORDERFILE_BUFFER_IDX_NAME_STR                               \
+  INSTR_PROF_QUOTE(INSTR_PROF_ORDERFILE_BUFFER_IDX_NAME)
+
 /* Macros to define start/stop section symbol for a given
  * section on Linux. For instance
  * INSTR_PROF_SECT_START(INSTR_PROF_DATA_SECT_NAME) will
@@ -725,6 +741,12 @@
 
 #endif /* INSTR_PROF_DATA_INC */
 
+#ifndef INSTR_ORDER_FILE_INC
+// The maximal # of functions: 128*1024 (the buffer size will be 128*4 KB).
+#define INSTR_ORDER_FILE_BUFFER_SIZE 131072
+#define INSTR_ORDER_FILE_BUFFER_BITS 17
+#define INSTR_ORDER_FILE_BUFFER_MASK 0x1ffff
+#endif /* INSTR_ORDER_FILE_INC */
 #else
 #undef INSTR_PROF_DATA_DEFINED
 #endif
Index: lib/profile/InstrProfiling.h
===================================================================
--- lib/profile/InstrProfiling.h
+++ lib/profile/InstrProfiling.h
@@ -64,6 +64,7 @@
 uint64_t *__llvm_profile_end_counters(void);
 ValueProfNode *__llvm_profile_begin_vnodes();
 ValueProfNode *__llvm_profile_end_vnodes();
+uint32_t *__llvm_profile_begin_orderfile();
 
 /*!
  * \brief Clear profile counters to zero.
@@ -120,6 +121,7 @@
  */
 int __llvm_profile_write_file(void);
 
+int __llvm_orderfile_write_file(void);
 /*!
  * \brief this is a wrapper interface to \c __llvm_profile_write_file.
  * After this interface is invoked, a arleady dumped flag will be set
@@ -142,6 +144,8 @@
  */
 int __llvm_profile_dump(void);
 
+int __llvm_orderfile_dump(void);
+
 /*!
  * \brief Set the filename for writing instrumentation data.
  *
Index: lib/profile/InstrProfilingFile.c
===================================================================
--- lib/profile/InstrProfilingFile.c
+++ lib/profile/InstrProfilingFile.c
@@ -111,6 +111,15 @@
   return 0;
 }
 
+/* TODO: make buffer size controllable by an internal option, and compiler can pass the size
+   to runtime via a variable. */
+static uint32_t orderFileWriter(FILE *File, const uint32_t *DataStart) {
+  if (fwrite(DataStart, sizeof(uint32_t), INSTR_ORDER_FILE_BUFFER_SIZE, File) !=
+      INSTR_ORDER_FILE_BUFFER_SIZE)
+    return 1;
+  return 0;
+}
+
 static void initFileWriter(ProfDataWriter *This, FILE *File) {
   This->Write = fileWriter;
   This->WriterCtx = File;
@@ -260,6 +269,27 @@
   return RetVal;
 }
 
+/* Write order data to file \c OutputName.  */
+static int writeOrderFile(const char *OutputName) {
+  int RetVal;
+  FILE *OutputFile;
+
+  OutputFile = fopen(OutputName, "w");
+
+  if (!OutputFile) {
+    PROF_WARN("can't open file with mode ab: %s\n", OutputName);
+    return -1;
+  }
+
+  FreeHook = &free;
+  setupIOBuffer();
+  const uint32_t *DataBegin = __llvm_profile_begin_orderfile();
+  RetVal = orderFileWriter(OutputFile, DataBegin);
+
+  fclose(OutputFile);
+  return RetVal;
+}
+
 static void truncateCurrentFile(void) {
   const char *Filename;
   char *FilenameBuf;
@@ -648,6 +678,62 @@
   return rc;
 }
 
+/* Order file data will be saved in a file with suffx .order. */
+static const char *OrderFileSuffix = ".order";
+
+COMPILER_RT_VISIBILITY
+int __llvm_orderfile_write_file(void) {
+  int rc, Length, LengthBeforeAppend, SuffixLength;
+  const char *Filename;
+  char *FilenameBuf;
+  int PDeathSig = 0;
+
+  SuffixLength = strlen(OrderFileSuffix);
+  Length = getCurFilenameLength() + SuffixLength;
+  FilenameBuf = (char *)COMPILER_RT_ALLOCA(Length + 1);
+  Filename = getCurFilename(FilenameBuf, 1);
+
+  /* Check the filename. */
+  if (!Filename) {
+    PROF_ERR("Failed to write file : %s\n", "Filename not set");
+    return -1;
+  }
+
+  /* Append order file suffix */
+  LengthBeforeAppend = strlen(Filename);
+  memcpy(FilenameBuf + LengthBeforeAppend, OrderFileSuffix, SuffixLength);
+  FilenameBuf[LengthBeforeAppend + SuffixLength] = '\0';
+
+  /* Check if there is llvm/runtime version mismatch.  */
+  if (GET_VERSION(__llvm_profile_get_version()) != INSTR_PROF_RAW_VERSION) {
+    PROF_ERR("Runtime and instrumentation version mismatch : "
+             "expected %d, but get %d\n",
+             INSTR_PROF_RAW_VERSION,
+             (int)GET_VERSION(__llvm_profile_get_version()));
+    return -1;
+  }
+
+  // Temporarily suspend getting SIGKILL when the parent exits.
+  PDeathSig = lprofSuspendSigKill();
+
+  /* Write order data to the file. */
+  rc = writeOrderFile(Filename);
+  if (rc)
+    PROF_ERR("Failed to write file \"%s\": %s\n", Filename, strerror(errno));
+
+  // Restore SIGKILL.
+  if (PDeathSig == 1)
+    lprofRestoreSigKill();
+
+  return rc;
+}
+
+COMPILER_RT_VISIBILITY
+int __llvm_orderfile_dump(void) {
+  int rc = __llvm_orderfile_write_file();
+  return rc;
+}
+
 static void writeFileWithoutReturn(void) { __llvm_profile_write_file(); }
 
 COMPILER_RT_VISIBILITY
Index: lib/profile/InstrProfilingPlatformDarwin.c
===================================================================
--- lib/profile/InstrProfilingPlatformDarwin.c
+++ lib/profile/InstrProfilingPlatformDarwin.c
@@ -27,6 +27,9 @@
 COMPILER_RT_VISIBILITY
 extern uint64_t
     CountersEnd __asm("section$end$__DATA$" INSTR_PROF_CNTS_SECT_NAME);
+COMPILER_RT_VISIBILITY
+extern uint32_t
+    OrderFileStart __asm("section$start$__DATA$" INSTR_PROF_ORDERFILE_SECT_NAME);
 
 COMPILER_RT_VISIBILITY
 extern ValueProfNode
@@ -49,6 +52,8 @@
 uint64_t *__llvm_profile_begin_counters(void) { return &CountersStart; }
 COMPILER_RT_VISIBILITY
 uint64_t *__llvm_profile_end_counters(void) { return &CountersEnd; }
+COMPILER_RT_VISIBILITY
+uint32_t *__llvm_profile_begin_orderfile(void) { return &OrderFileStart; }
 
 COMPILER_RT_VISIBILITY
 ValueProfNode *__llvm_profile_begin_vnodes(void) {
Index: test/profile/Inputs/instrprof-order-file-2.c
===================================================================
--- test/profile/Inputs/instrprof-order-file-2.c
+++ test/profile/Inputs/instrprof-order-file-2.c
@@ -0,0 +1,7 @@
+__attribute__((noinline)) int f(int a) {
+  return a + 1;
+}
+
+__attribute__((noinline)) int g(int a) {
+  return a + 2;
+}
Index: test/profile/Inputs/instrprof-order-file.c
===================================================================
--- test/profile/Inputs/instrprof-order-file.c
+++ test/profile/Inputs/instrprof-order-file.c
@@ -0,0 +1,17 @@
+void __llvm_profile_initialize_file(void);
+int __llvm_orderfile_dump(void);
+
+__attribute__((noinline)) int f(int a);
+
+__attribute__((noinline)) int g(int a);
+
+int main(int argc, const char *argv[]) {
+  int a = f(argc);
+  int t = 0;
+  for (int i = 0; i < argc; i++)
+    t += g(a);
+  f(t);
+  __llvm_profile_initialize_file();
+  __llvm_orderfile_dump();
+  return 0;
+}
Index: test/profile/instrprof-order-file.test
===================================================================
--- test/profile/instrprof-order-file.test
+++ test/profile/instrprof-order-file.test
@@ -0,0 +1,16 @@
+// UNSUPPORTED: windows
+// RUN: rm -rf %t.dir && mkdir -p %t.dir
+// RUN: cd %t.dir
+//
+// RUN: %clang -forder-file-instrumentation -O1 -o %t.2 %S/Inputs/instrprof-order-file-2.c %S/Inputs/instrprof-order-file.c -mllvm -orderfile-write-mapping="mapping.txt"
+// RUN: %run %t.2 ANY
+// RUN: od -h default.profraw.order | FileCheck %s
+// RUN: cat mapping.txt | FileCheck %s --check-prefix=MAPPING
+
+// Make sure we have MD5 for main, then f, then g.
+// CHECK: 0000000      d5fa    e78d    6436    db95    a18f    dd4c    4f75    cc91
+// CHECK: 0000020      f5b2    47ff    6643    b671    0000    0000    0000    0000
+
+// MAPPING: MD5 cc914f75dd4ca18f f
+// MAPPING: MD5 b671664347fff5b2 g
+// MAPPING: MD5 db956436e78dd5fa main