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: lib/profile/InstrProfilingPlatformLinux.c
===================================================================
--- lib/profile/InstrProfilingPlatformLinux.c
+++ lib/profile/InstrProfilingPlatformLinux.c
@@ -19,6 +19,7 @@
 #define PROF_NAME_STOP INSTR_PROF_SECT_STOP(INSTR_PROF_NAME_COMMON)
 #define PROF_CNTS_START INSTR_PROF_SECT_START(INSTR_PROF_CNTS_COMMON)
 #define PROF_CNTS_STOP INSTR_PROF_SECT_STOP(INSTR_PROF_CNTS_COMMON)
+#define PROF_ORDERFILE_START INSTR_PROF_SECT_START(INSTR_PROF_ORDERFILE_COMMON)
 #define PROF_VNODES_START INSTR_PROF_SECT_START(INSTR_PROF_VNODES_COMMON)
 #define PROF_VNODES_STOP INSTR_PROF_SECT_STOP(INSTR_PROF_VNODES_COMMON)
 
@@ -29,6 +30,7 @@
 extern __llvm_profile_data PROF_DATA_STOP COMPILER_RT_VISIBILITY;
 extern uint64_t PROF_CNTS_START COMPILER_RT_VISIBILITY;
 extern uint64_t PROF_CNTS_STOP COMPILER_RT_VISIBILITY;
+extern uint32_t PROF_ORDERFILE_START COMPILER_RT_VISIBILITY;
 extern char PROF_NAME_START COMPILER_RT_VISIBILITY;
 extern char PROF_NAME_STOP COMPILER_RT_VISIBILITY;
 extern ValueProfNode PROF_VNODES_START COMPILER_RT_VISIBILITY;
@@ -62,6 +64,9 @@
 COMPILER_RT_VISIBILITY uint64_t *__llvm_profile_end_counters(void) {
   return &PROF_CNTS_STOP;
 }
+COMPILER_RT_VISIBILITY uint32_t *__llvm_profile_begin_orderfile(void) {
+  return &PROF_ORDERFILE_START;
+}
 
 COMPILER_RT_VISIBILITY ValueProfNode *
 __llvm_profile_begin_vnodes(void) {
Index: lib/profile/InstrProfilingPlatformOther.c
===================================================================
--- lib/profile/InstrProfilingPlatformOther.c
+++ lib/profile/InstrProfilingPlatformOther.c
@@ -21,6 +21,7 @@
 static const char *NamesLast = NULL;
 static uint64_t *CountersFirst = NULL;
 static uint64_t *CountersLast = NULL;
+static uint32_t *OrderFileFirst = NULL;
 
 static const void *getMinAddr(const void *A1, const void *A2) {
   return A1 < A2 ? A1 : A2;
@@ -82,6 +83,9 @@
 uint64_t *__llvm_profile_begin_counters(void) { return CountersFirst; }
 COMPILER_RT_VISIBILITY
 uint64_t *__llvm_profile_end_counters(void) { return CountersLast; }
+/* TODO: correctly set up OrderFileFirst. */
+COMPILER_RT_VISIBILITY
+uint32_t *__llvm_profile_begin_orderfile(void) { return OrderFileFirst; }
 
 COMPILER_RT_VISIBILITY
 ValueProfNode *__llvm_profile_begin_vnodes(void) {
Index: lib/profile/InstrProfilingPlatformWindows.c
===================================================================
--- lib/profile/InstrProfilingPlatformWindows.c
+++ lib/profile/InstrProfilingPlatformWindows.c
@@ -29,6 +29,7 @@
 #pragma section(".lprfd$Z", read, write)
 #pragma section(".lprfc$A", read, write)
 #pragma section(".lprfc$Z", read, write)
+#pragma section(".lorderfile$A", read, write)
 #pragma section(".lprfnd$A", read, write)
 #pragma section(".lprfnd$Z", read, write)
 #endif
@@ -41,6 +42,7 @@
 
 uint64_t COMPILER_RT_SECTION(".lprfc$A") CountersStart;
 uint64_t COMPILER_RT_SECTION(".lprfc$Z") CountersEnd;
+uint32_t COMPILER_RT_SECTION(".lorderfile$A") OrderFileStart;
 
 ValueProfNode COMPILER_RT_SECTION(".lprfnd$A") VNodesStart;
 ValueProfNode COMPILER_RT_SECTION(".lprfnd$Z") VNodesEnd;
@@ -55,6 +57,7 @@
 
 uint64_t *__llvm_profile_begin_counters(void) { return &CountersStart + 1; }
 uint64_t *__llvm_profile_end_counters(void) { return &CountersEnd; }
+uint32_t *__llvm_profile_begin_orderfile(void) { return &OrderFileStart; }
 
 ValueProfNode *__llvm_profile_begin_vnodes(void) { return &VNodesStart + 1; }
 ValueProfNode *__llvm_profile_end_vnodes(void) { return &VNodesEnd; }