diff --git a/compiler-rt/lib/profile/InstrProfiling.h b/compiler-rt/lib/profile/InstrProfiling.h
--- a/compiler-rt/lib/profile/InstrProfiling.h
+++ b/compiler-rt/lib/profile/InstrProfiling.h
@@ -10,6 +10,7 @@
 #define PROFILE_INSTRPROFILING_H_
 
 #include "InstrProfilingPort.h"
+#include <stdio.h>
 
 #define INSTR_PROF_VISIBILITY COMPILER_RT_VISIBILITY
 #include "InstrProfData.inc"
@@ -125,7 +126,7 @@
 /*!
  * \brief this is a wrapper interface to \c __llvm_profile_write_file.
  * After this interface is invoked, a arleady dumped flag will be set
- * so that profile won't be dumped again during program exit. 
+ * so that profile won't be dumped again during program exit.
  * Invocation of interface __llvm_profile_reset_counters will clear
  * the flag. This interface is designed to be used to collect profile
  * data from user selected hot regions. The use model is
@@ -157,6 +158,23 @@
  */
 void __llvm_profile_set_filename(const char *Name);
 
+/*!
+ * \brief Set the FILE object for writing instrumentation data.
+ *
+ * Sets the FILE object to be used for subsequent calls to
+ * \a __llvm_profile_write_file(). The profile file name set by environment
+ * variable, command-line option, or calls to \a  __llvm_profile_set_filename
+ * will be ignored.
+ *
+ * \c File will not be closed after a call to \a __llvm_profile_write_file() but
+ * it may be flushed. Passing NULL restores default behavior.
+ *
+ * \c If IsExclusive is nonzero, the runtime will assume that it has exclusive
+ * access to the file, even among other processes, and thus it is safe to use
+ * the file for online merging if it would normally do so.
+ */
+void __llvm_profile_set_file_object(FILE *File, int IsExclusive);
+
 /*! \brief Register to write instrumentation data to file at exit. */
 int __llvm_profile_register_write_file_atexit(void);
 
diff --git a/compiler-rt/lib/profile/InstrProfilingFile.c b/compiler-rt/lib/profile/InstrProfilingFile.c
--- a/compiler-rt/lib/profile/InstrProfilingFile.c
+++ b/compiler-rt/lib/profile/InstrProfilingFile.c
@@ -37,7 +37,7 @@
 /* From where is profile name specified.
  * The order the enumerators define their
  * precedence. Re-order them may lead to
- * runtime behavior change. */ 
+ * runtime behavior change. */
 typedef enum ProfileNameSpecifier {
   PNS_unknown = 0,
   PNS_default,
@@ -89,9 +89,32 @@
 COMPILER_RT_WEAK lprofFilename lprofCurFilename = {0,   0, 0, 0, {0},
                                                    {0}, 0, 0, 0, PNS_unknown};
 
+static int ProfileFileSafeToMerge = 0;
+static int lprofIsProfileFileSafeToMerge() { return ProfileFileSafeToMerge; }
+static void lprofSetProfileFileSafeToMerge(int IsSafe) {
+  return ProfileFileSafeToMerge;
+}
+
+static FILE *ProfileFile = NULL;
+static FILE *lprofGetProfileFile() { return ProfileFile; }
+static void lprofSetProfileFile(FILE *File) {
+  ProfileFile = File;
+}
+
+COMPILER_RT_VISIBILITY void __llvm_profile_set_file_object(FILE *File,
+                                                           int IsExclusive) {
+  lprofSetProfileFile(File);
+  lprofSetProfileFileSafeToMerge(IsExclusive);
+}
+
 static int getCurFilenameLength();
 static const char *getCurFilename(char *FilenameBuf, int ForceUseBuf);
-static unsigned doMerging() { return lprofCurFilename.MergePoolSize; }
+static unsigned doMerging() {
+  if (lprofGetProfileFile() != NULL && !lprofIsProfileFileSafeToMerge()) {
+    return 0;
+  }
+  return lprofCurFilename.MergePoolSize;
+}
 
 /* Return 1 if there is an error, otherwise return  0.  */
 static uint32_t fileWriter(ProfDataWriter *This, ProfDataIOVec *IOVecs,
@@ -228,8 +251,11 @@
   FILE *ProfileFile;
   int rc;
 
-  createProfileDir(ProfileFileName);
-  ProfileFile = lprofOpenFileEx(ProfileFileName);
+  ProfileFile = lprofGetProfileFile();
+  if (!ProfileFile) {
+    createProfileDir(ProfileFileName);
+    ProfileFile = lprofOpenFileEx(ProfileFileName);
+  }
   if (!ProfileFile)
     return NULL;
 
@@ -244,17 +270,28 @@
   return ProfileFile;
 }
 
+static FILE* GetFileObject(const char *OutputName) {
+  FILE* File;
+  File = lprofGetProfileFile();
+  if (File != NULL) {
+    return File;
+  }
+
+  return fopen(OutputName, "ab");
+}
+
 /* Write profile data to file \c OutputName.  */
 static int writeFile(const char *OutputName) {
   int RetVal;
   FILE *OutputFile;
+  FILE *ProfileFilePtr;
 
   int MergeDone = 0;
   VPMergeHook = &lprofMergeValueProfData;
-  if (!doMerging())
-    OutputFile = fopen(OutputName, "ab");
-  else
+  if (doMerging())
     OutputFile = openFileForMerging(OutputName, &MergeDone);
+  else
+    OutputFile = GetFileObject(OutputName);
 
   if (!OutputFile)
     return -1;
@@ -265,7 +302,10 @@
   initFileWriter(&fileWriter, OutputFile);
   RetVal = lprofWriteData(&fileWriter, lprofGetVPDataReader(), MergeDone);
 
-  fclose(OutputFile);
+  if (ProfileFilePtr == NULL)
+    fclose(OutputFile);
+  else
+    fflush(OutputFile);
   return RetVal;
 }
 
@@ -591,7 +631,7 @@
 
   EnvFilenamePat = getFilenamePatFromEnv();
   if (EnvFilenamePat) {
-    /* Pass CopyFilenamePat = 1, to ensure that the filename would be valid 
+    /* Pass CopyFilenamePat = 1, to ensure that the filename would be valid
        at the  moment when __llvm_profile_write_file() gets executed. */
     parseAndSetFilename(EnvFilenamePat, PNS_environment, 1);
     return;
@@ -627,8 +667,7 @@
   int PDeathSig = 0;
 
   if (lprofProfileDumped()) {
-    PROF_NOTE("Profile data not written to file: %s.\n", 
-              "already written");
+    PROF_NOTE("Profile data not written to file: %s.\n", "already written");
     return 0;
   }
 
diff --git a/compiler-rt/test/profile/instrprof-set-file-object.c b/compiler-rt/test/profile/instrprof-set-file-object.c
new file mode 100644
--- /dev/null
+++ b/compiler-rt/test/profile/instrprof-set-file-object.c
@@ -0,0 +1,18 @@
+// Test that the specified output has profiling data.
+// RUN: %clang_profgen -o %t -O3 %s
+// RUN: %run %t %t.file.profraw
+// RUN: test -f %t.file.profraw
+// RUN: llvm-profdata show %t.file.profraw
+// RUN: rm %t.file.profraw
+#include <stdio.h>
+
+extern void __llvm_profile_set_file_object(FILE*);
+
+int main(int argc, const char *argv[]) {
+  if (argc < 2)
+    return 1;
+
+  FILE* F = fopen(argv[1], "w+b");
+  __llvm_profile_set_file_object(F);
+  return 0;
+}