Index: lib/profile/InstrProfData.inc
===================================================================
--- lib/profile/InstrProfData.inc
+++ lib/profile/InstrProfData.inc
@@ -266,7 +266,9 @@
 INSTR_PROF_SECT_ENTRY(IPSK_covmap, \
                       INSTR_PROF_QUOTE(INSTR_PROF_COVMAP_COMMON), \
                       INSTR_PROF_QUOTE(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
 
@@ -655,6 +657,7 @@
 #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
 /* Win32 */
 #define INSTR_PROF_DATA_COFF .lprfd
 #define INSTR_PROF_NAME_COFF .lprfn
@@ -662,6 +665,7 @@
 #define INSTR_PROF_VALS_COFF .lprfv
 #define INSTR_PROF_VNODES_COFF .lprfnd
 #define INSTR_PROF_COVMAP_COFF .lcovmap
+#define INSTR_PROF_ORDERFILE_COFF .lorderfile
 
 #ifdef _WIN32
 /* Runtime section names and name strings.  */
@@ -675,6 +679,8 @@
 /* Value profile nodes section. */
 #define INSTR_PROF_VNODES_SECT_NAME INSTR_PROF_VNODES_COFF
 #define INSTR_PROF_COVMAP_SECT_NAME INSTR_PROF_COVMAP_COFF
+/* Order file for Pika. */
+#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_DATA_COMMON
@@ -687,6 +693,8 @@
 /* Value profile nodes section. */
 #define INSTR_PROF_VNODES_SECT_NAME INSTR_PROF_VNODES_COMMON
 #define INSTR_PROF_COVMAP_SECT_NAME INSTR_PROF_COVMAP_COMMON
+/* Order file for Pika. */
+#define INSTR_PROF_ORDERFILE_SECT_NAME INSTR_PROF_ORDERFILE_COMMON
 #endif
 
 #define INSTR_PROF_DATA_SECT_NAME_STR                                          \
@@ -701,6 +709,8 @@
   INSTR_PROF_QUOTE(INSTR_PROF_VALS_SECT_NAME)
 #define INSTR_PROF_VNODES_SECT_NAME_STR                                        \
   INSTR_PROF_QUOTE(INSTR_PROF_VNODES_SECT_NAME)
+#define INSTR_PROF_ORDERFILE_SECT_NAME_STR                                     \
+  INSTR_PROF_QUOTE(INSTR_PROF_ORDERFILE_SECT_NAME)
 
 /* Macros to define start/stop section symbol for a given
  * section on Linux. For instance
@@ -735,6 +745,12 @@
 
 #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
@@ -65,6 +65,7 @@
 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.
@@ -121,6 +122,7 @@
  */
 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
@@ -143,6 +145,8 @@
  */
 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
@@ -112,6 +112,13 @@
   return 0;
 }
 
+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;
@@ -261,6 +268,25 @@
   return RetVal;
 }
 
+/* Write order data to file \c OutputName.  */
+static int writeOrderFile(const char *OutputName) {
+  int RetVal;
+  FILE *OutputFile;
+
+  OutputFile = fopen(OutputName, "ab");
+
+  if (!OutputFile)
+    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;
@@ -649,6 +675,53 @@
   return rc;
 }
 
+COMPILER_RT_VISIBILITY
+int __llvm_orderfile_write_file(void) {
+  int rc, Length;
+  const char *Filename;
+  char *FilenameBuf;
+  int PDeathSig = 0;
+
+  Length = getCurFilenameLength();
+  FilenameBuf = (char *)COMPILER_RT_ALLOCA(Length + 1);
+  Filename = getCurFilename(FilenameBuf, 0);
+
+  /* Check the filename. */
+  if (!Filename) {
+    PROF_ERR("Failed to write file : %s\n", "Filename not set");
+    return -1;
+  }
+
+  /* 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
@@ -28,6 +28,9 @@
 COMPILER_RT_VISIBILITY
 extern uint64_t
     CountersEnd __asm("section$end$__DATA$" INSTR_PROF_CNTS_SECT_NAME_STR);
+COMPILER_RT_VISIBILITY
+extern uint32_t OrderFileStart __asm(
+    "section$start$__DATA$" INSTR_PROF_ORDERFILE_SECT_NAME_STR);
 
 COMPILER_RT_VISIBILITY
 extern ValueProfNode
@@ -50,6 +53,8 @@
 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) {