Index: CMakeLists.txt
===================================================================
--- CMakeLists.txt
+++ CMakeLists.txt
@@ -208,6 +208,7 @@
 #================================
 include(CheckIncludeFile)
 check_include_file(unwind.h HAVE_UNWIND_H)
+check_include_file(mpi.h HAVE_MPI_H)
 
 include(config-ix)
 
Index: lib/profile/CMakeLists.txt
===================================================================
--- lib/profile/CMakeLists.txt
+++ lib/profile/CMakeLists.txt
@@ -36,7 +36,9 @@
   InstrProfilingPlatformDarwin.c
   InstrProfilingPlatformLinux.c
   InstrProfilingPlatformOther.c
+  InstrProfilingReduce.c
   InstrProfilingRuntime.cc
+  InstrProfilingStub.c
   InstrProfilingUtil.c)
 
 if(WIN32)
@@ -55,6 +57,12 @@
      -DCOMPILER_RT_HAS_ATOMICS=1)
 endif() 
 
+if(HAVE_MPI_H)
+ set(EXTRA_FLAGS
+     ${EXTRA_FLAGS}
+     -DHAVE_MPI_H=1)
+endif() 
+
 if(APPLE)
   add_compiler_rt_runtime(clang_rt.profile
     STATIC
Index: lib/profile/InstrProfilingFile.c
===================================================================
--- lib/profile/InstrProfilingFile.c
+++ lib/profile/InstrProfilingFile.c
@@ -15,8 +15,19 @@
 #include <stdlib.h>
 #include <string.h>
 
+#ifndef _MSC_VER
+#include <unistd.h>
+#include <fcntl.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#endif
+
 #define UNCONST(ptr) ((void *)(uintptr_t)(ptr))
 
+#ifdef HAVE_MPI_H
+COMPILER_RT_VISIBILITY extern int __llvm_write_prof_data;
+#endif
+
 /* Return 1 if there is an error, otherwise return  0.  */
 static uint32_t fileWriter(ProfDataIOVec *IOVecs, uint32_t NumIOVecs,
                            void **WriterCtx) {
@@ -72,7 +83,11 @@
 
 static void truncateCurrentFile(void) {
   const char *Filename;
+#ifdef _MSC_VER
   FILE *File;
+#else
+  int File;
+#endif
 
   Filename = __llvm_profile_CurrentFilename;
   if (!Filename || !Filename[0])
@@ -86,11 +101,20 @@
     free(Copy);
   }
 
+#ifdef _MSC_VER
   /* Truncate the file.  Later we'll reopen and append. */
   File = fopen(Filename, "w");
   if (!File)
     return;
   fclose(File);
+#else
+  /* O_CREAT is not included to avoid creating empty files.
+     In MPI applications, a file will only be created by one process */
+  File = open(Filename, O_WRONLY | O_TRUNC);
+  if (File == -1)
+      return;
+  close(File);
+#endif
 }
 
 static void setFilename(const char *Filename, int OwnsFilename) {
@@ -216,6 +240,11 @@
 
 COMPILER_RT_VISIBILITY
 int __llvm_profile_write_file(void) {
+  
+#ifdef HAVE_MPI_H
+  if (!__llvm_write_prof_data)
+      return 0;
+#endif
   int rc;
 
   GetEnvHook = &getenv;
Index: lib/profile/InstrProfilingReduce.c
===================================================================
--- /dev/null
+++ lib/profile/InstrProfilingReduce.c
@@ -0,0 +1,34 @@
+/*===- InstrProfilingReduce.c - Support library for applications using MPI ===*\
+|*
+|*                     The LLVM Compiler Infrastructure
+|*
+|* This file is distributed under the University of Illinois Open Source
+|* License. See LICENSE.TXT for details.
+|*
+\*===----------------------------------------------------------------------===*/
+
+#include <stdlib.h>
+#include <InstrProfiling.h>
+
+#ifdef HAVE_MPI_H
+#include <mpi.h>
+COMPILER_RT_VISIBILITY int __llvm_write_prof_data = 1;
+COMPILER_RT_VISIBILITY int MPI_Finalize() {
+   int Rank;
+   uint64_t *CountersBegin = __llvm_profile_begin_counters();
+   uint64_t *CountersEnd = __llvm_profile_end_counters();
+   uint64_t CountersSize = CountersEnd - CountersBegin;
+
+   MPI_Comm_rank(MPI_COMM_WORLD, &Rank);
+   if (Rank) {
+      MPI_Reduce(CountersBegin, NULL, CountersSize, MPI_UINT64_T, MPI_SUM,
+              0, MPI_COMM_WORLD);
+      __llvm_write_prof_data = 0;
+   } else
+      MPI_Reduce(MPI_IN_PLACE, CountersBegin, CountersSize, MPI_UINT64_T, MPI_SUM,
+              0, MPI_COMM_WORLD);
+   return PMPI_Finalize();
+}
+
+#endif
+
Index: lib/profile/InstrProfilingStub.c
===================================================================
--- /dev/null
+++ lib/profile/InstrProfilingStub.c
@@ -0,0 +1,14 @@
+/*===- InstrProfilingStub.c - Stubs for applications not using MPI --------===*\
+|*
+|*                     The LLVM Compiler Infrastructure
+|*
+|* This file is distributed under the University of Illinois Open Source
+|* License. See LICENSE.TXT for details.
+|*
+\*===----------------------------------------------------------------------===*/
+
+#include <stdlib.h>
+
+void MPI_Comm_rank(void *Comm, int *Rank) { abort(); }
+void MPI_Reduce() { abort(); }
+void PMPI_Finalize() { abort(); }
Index: test/profile/instrprof-reduce.c
===================================================================
--- /dev/null
+++ test/profile/instrprof-reduce.c
@@ -0,0 +1,24 @@
+// RUN: %clang_profgen -o %t -O3 %s
+// RUN: rm -f %t.profraw
+// RUN: env LLVM_PROFILE_FILE=%t.profraw %run %t 0
+// RUN: test -e %t.profraw
+// RUN: rm -f %t.profraw
+// RUN: env LLVM_PROFILE_FILE=%t.profraw %run %t 1
+// RUN: test ! -e %t.profraw
+// REQUIRES: shell
+
+#include <stdlib.h>
+#include <stdio.h>
+int ThisRank;
+int MPI_Comm_rank(void *Comm, int *Rank) { *Rank = ThisRank; return 0; }
+int MPI_Reduce() { return 0; }
+int PMPI_Finalize() { return 0; }
+int MPI_Finalize();
+
+int main(int argc, const char *argv[]) {
+printf("in main\n");
+  ThisRank = atoi(argv[1]);
+  MPI_Finalize();
+  return 0;
+}
+