Index: include/llvm/ProfileData/InstrProf.h
===================================================================
--- include/llvm/ProfileData/InstrProf.h
+++ include/llvm/ProfileData/InstrProf.h
@@ -30,7 +30,7 @@
 #include <system_error>
 #include <vector>
 
-#define INSTR_PROF_INDEX_VERSION 3
+#define INSTR_PROF_INDEX_VERSION 4
 namespace llvm {
 
 class Function;
Index: lib/ProfileData/InstrProf.cpp
===================================================================
--- lib/ProfileData/InstrProf.cpp
+++ lib/ProfileData/InstrProf.cpp
@@ -74,14 +74,15 @@
 
 std::string getPGOFuncName(StringRef RawFuncName,
                            GlobalValue::LinkageTypes Linkage,
-                           StringRef FileName,
-                           uint64_t Version LLVM_ATTRIBUTE_UNUSED) {
+                           StringRef FileName, uint64_t Version) {
 
   // Function names may be prefixed with a binary '1' to indicate
   // that the backend should not modify the symbols due to any platform
   // naming convention. Do not include that '1' in the PGO profile name.
   if (RawFuncName[0] == '\1')
     RawFuncName = RawFuncName.substr(1);
+  const char *Unknown = (Version <= 3 ? "<unknown>:" : "__unknown__");
+  const char *Sep = (Version <= 3 ? ":" : "__");
 
   std::string FuncName = RawFuncName;
   if (llvm::GlobalValue::isLocalLinkage(Linkage)) {
@@ -90,9 +91,9 @@
     // that it will stay the same, e.g., if the files are checked out from
     // version control in different locations.
     if (FileName.empty())
-      FuncName = FuncName.insert(0, "<unknown>:");
+      FuncName = FuncName.insert(0, Unknown);
     else
-      FuncName = FuncName.insert(0, FileName.str() + ":");
+      FuncName = FuncName.insert(0, FileName.str() + Sep);
   }
   return FuncName;
 }
Index: test/tools/llvm-profdata/compat.proftext
===================================================================
--- test/tools/llvm-profdata/compat.proftext
+++ test/tools/llvm-profdata/compat.proftext
@@ -65,3 +65,10 @@
 # FORMATV2-NEXT: Maximum internal block count: 1000000
 
 
+# RUN: llvm-profdata show %S/Inputs/compat.profdata.v4 -all-functions --counts | FileCheck %s -check-prefix=FORMATV4
+# FORMATV4:  instrprof.c__foo_static:
+# FORMATV4-NEXT:    Hash: 0x000000000000000a
+# FORMATV4-NEXT:    Counters: 2
+# FORMATV4-NEXT:    Function count: 500500
+# FORMATV4-NEXT:    Block counts: [180100]
+