Index: include/llvm/Analysis/ProfileSummaryInfo.h
===================================================================
--- include/llvm/Analysis/ProfileSummaryInfo.h
+++ include/llvm/Analysis/ProfileSummaryInfo.h
@@ -102,8 +102,11 @@
   bool isFunctionHotInCallGraph(const Function *F, BlockFrequencyInfo &BFI);
   /// Returns true if \p F has cold function entry.
   bool isFunctionEntryCold(const Function *F);
-  /// Returns true if \p F contains only cold code.
-  bool isFunctionColdInCallGraph(const Function *F, BlockFrequencyInfo &BFI);
+  /// Returns true if \p F contains only cold code. If returns false,
+  /// IsUnknown will tell whether the function is not cold for sure or
+  /// just unknown.
+  bool isFunctionColdInCallGraph(const Function *F, BlockFrequencyInfo &BFI,
+                                 bool &IsUnknown);
   /// Returns true if count \p C is considered hot.
   bool isHotCount(uint64_t C);
   /// Returns true if count \p C is considered cold.
Index: lib/Analysis/ProfileSummaryInfo.cpp
===================================================================
--- lib/Analysis/ProfileSummaryInfo.cpp
+++ lib/Analysis/ProfileSummaryInfo.cpp
@@ -164,12 +164,16 @@
 /// If it returns false, it either means it is not cold or it is unknown
 /// (for example, no profile data is available).
 bool ProfileSummaryInfo::isFunctionColdInCallGraph(const Function *F,
-                                                   BlockFrequencyInfo &BFI) {
+                                                   BlockFrequencyInfo &BFI,
+                                                   bool &IsUnknown) {
   if (!F || !computeSummary())
     return false;
-  if (auto FunctionCount = F->getEntryCount())
+  IsUnknown = true;
+  if (auto FunctionCount = F->getEntryCount()) {
+    IsUnknown = false;
     if (!isColdCount(FunctionCount.getCount()))
       return false;
+  }
 
   if (hasSampleProfile()) {
     uint64_t TotalCallCount = 0;
Index: lib/CodeGen/CodeGenPrepare.cpp
===================================================================
--- lib/CodeGen/CodeGenPrepare.cpp
+++ lib/CodeGen/CodeGenPrepare.cpp
@@ -173,6 +173,17 @@
     "profile-guided-section-prefix", cl::Hidden, cl::init(true), cl::ZeroOrMore,
     cl::desc("Use profile info to add section prefix for hot/cold functions"));
 
+static cl::opt<bool> ProfileUnknownInSpecialSection(
+    "profile-unknown-in-special-section", cl::Hidden, cl::init(false),
+    cl::ZeroOrMore,
+    cl::desc("When profile info is used to add section prefix for hot/cold "
+             "functions. In sample profile, we cannot tell a function is "
+             "cold for sure if we don't have profile unless "
+             "option profile-sample-accurate is used, because it is possible "
+             "that the function lacking profile is newly created. With the "
+             "option, the function with its hot/cold being unknown will be "
+             "put in a special section instead of '.text' section. "));
+
 static cl::opt<unsigned> FreqRatioToSkipMerge(
     "cgp-freq-ratio-to-skip-merge", cl::Hidden, cl::init(2),
     cl::desc("Skip merging empty blocks if (frequency of empty block) / "
@@ -432,10 +443,13 @@
   ProfileSummaryInfo *PSI =
       &getAnalysis<ProfileSummaryInfoWrapperPass>().getPSI();
   if (ProfileGuidedSectionPrefix) {
+    bool IsUnknown = false;
     if (PSI->isFunctionHotInCallGraph(&F, *BFI))
       F.setSectionPrefix(".hot");
-    else if (PSI->isFunctionColdInCallGraph(&F, *BFI))
+    else if (PSI->isFunctionColdInCallGraph(&F, *BFI, IsUnknown))
       F.setSectionPrefix(".unlikely");
+    else if (ProfileUnknownInSpecialSection && IsUnknown)
+      F.setSectionPrefix(".unknown");
   }
 
   /// This optimization identifies DIV instructions that can be
Index: lib/Transforms/Utils/SizeOpts.cpp
===================================================================
--- lib/Transforms/Utils/SizeOpts.cpp
+++ lib/Transforms/Utils/SizeOpts.cpp
@@ -25,7 +25,9 @@
   assert(F);
   if (!PSI || !BFI || !PSI->hasProfileSummary())
     return false;
-  return ProfileGuidedSizeOpt && PSI->isFunctionColdInCallGraph(F, *BFI);
+  bool IsUnknown;
+  return ProfileGuidedSizeOpt &&
+         PSI->isFunctionColdInCallGraph(F, *BFI, IsUnknown);
 }
 
 bool llvm::shouldOptimizeForSize(BasicBlock *BB, ProfileSummaryInfo *PSI,
Index: test/Transforms/SampleProfile/section-accurate-samplepgo.ll
===================================================================
--- test/Transforms/SampleProfile/section-accurate-samplepgo.ll
+++ test/Transforms/SampleProfile/section-accurate-samplepgo.ll
@@ -1,4 +1,5 @@
 ; RUN: opt < %s -sample-profile -sample-profile-file=%S/Inputs/inline.prof -codegenprepare -S | FileCheck %s
+; RUN: opt < %s -sample-profile -sample-profile-file=%S/Inputs/inline.prof -codegenprepare -profile-unknown-in-special-section -S | FileCheck %s --check-prefix UNKNOWN
 ; RUN: opt < %s -sample-profile -sample-profile-file=%S/Inputs/inline.prof -codegenprepare -profile-sample-accurate -S | FileCheck %s --check-prefix ACCURATE
 
 target triple = "x86_64-pc-linux-gnu"
@@ -10,7 +11,8 @@
 declare void @hot_func()
 
 ; CHECK-NOT: foo_not_in_profile{{.*}}!section_prefix
-; CHECK: foo_not_in_profile{{.*}}!prof ![[UNKNOWN_ID:[0-9]+]]
+; CHECK: foo_not_in_profile{{.*}}!prof ![[NOPROFILE_ID:[0-9]+]]
+; UNKNOWN: foo_not_in_profile{{.*}}!prof ![[NOPROFILE_ID:[0-9]+]] !section_prefix ![[UNKNOWN_ID:[0-9]+]]
 ; ACCURATE: foo_not_in_profile{{.*}}!prof ![[ZERO_ID:[0-9]+]] !section_prefix ![[COLD_ID:[0-9]+]]
 ; The function not appearing in profile is cold when -profile-sample-accurate
 ; is on.
@@ -30,9 +32,11 @@
 
 attributes #0 = { "profile-sample-accurate" }
 
-; CHECK: ![[UNKNOWN_ID]] = !{!"function_entry_count", i64 -1}
+; CHECK: ![[NOPROFILE_ID]] = !{!"function_entry_count", i64 -1}
 ; CHECK: ![[ZERO_ID]] = !{!"function_entry_count", i64 0}
 ; CHECK: ![[COLD_ID]] = !{!"function_section_prefix", !".unlikely"}
+; UNKNOWN: ![[NOPROFILE_ID]] = !{!"function_entry_count", i64 -1}
+; UNKNOWN: ![[UNKNOWN_ID]] = !{!"function_section_prefix", !".unknown"}
 ; ACCURATE: ![[ZERO_ID]] = !{!"function_entry_count", i64 0}
 ; ACCURATE: ![[COLD_ID]] = !{!"function_section_prefix", !".unlikely"}
 !llvm.module.flags = !{!1}