Index: include/llvm/CodeGen/StackProtector.h
===================================================================
--- include/llvm/CodeGen/StackProtector.h
+++ include/llvm/CodeGen/StackProtector.h
@@ -19,6 +19,7 @@
 
 #include "llvm/ADT/SmallPtrSet.h"
 #include "llvm/ADT/Triple.h"
+#include "llvm/IR/DiagnosticInfo.h"
 #include "llvm/IR/Dominators.h"
 #include "llvm/IR/ValueMap.h"
 #include "llvm/Pass.h"
@@ -134,6 +135,36 @@
 
   bool runOnFunction(Function &Fn) override;
 };
+
+/// Diagnostic information for why SSP was applied.
+class DiagnosticInfoSSP : public DiagnosticInfoWithDebugLocBase {
+public:
+  enum SSPReason {
+    Unknown = 0,
+    Alloca = 1,
+    BufferOrStruct = 2,
+    AddressTaken = 3,
+    Attribute = 4
+  };
+
+  /// \p Fn is the function where the diagnostic is being emitted. \p Reason is
+  /// an enum value representing why the function has stack protection.
+  DiagnosticInfoSSP(const Function &Fn, SSPReason Reason)
+      : DiagnosticInfoWithDebugLocBase(DK_SSPReason, DS_Remark, Fn, DebugLoc()),
+        Func(Fn), Why(Reason) {}
+
+  static bool classof(const DiagnosticInfo *DI) {
+    return DI->getKind() == DK_SSPReason;
+  }
+
+  void print(DiagnosticPrinter &DP) const override;
+
+  SSPReason Reason() const { return Why; }
+
+private:
+  const Function &Func;
+  const SSPReason Why;
+};
 } // end namespace llvm
 
 #endif // LLVM_CODEGEN_STACKPROTECTOR_H
Index: include/llvm/IR/DiagnosticInfo.h
===================================================================
--- include/llvm/IR/DiagnosticInfo.h
+++ include/llvm/IR/DiagnosticInfo.h
@@ -72,6 +72,7 @@
   DK_MIRParser,
   DK_PGOProfile,
   DK_Unsupported,
+  DK_SSPReason,
   DK_FirstPluginKind
 };
 
Index: lib/CodeGen/StackProtector.cpp
===================================================================
--- lib/CodeGen/StackProtector.cpp
+++ lib/CodeGen/StackProtector.cpp
@@ -26,6 +26,7 @@
 #include "llvm/IR/DataLayout.h"
 #include "llvm/IR/DebugInfo.h"
 #include "llvm/IR/DerivedTypes.h"
+#include "llvm/IR/DiagnosticPrinter.h"
 #include "llvm/IR/Function.h"
 #include "llvm/IR/GlobalValue.h"
 #include "llvm/IR/GlobalVariable.h"
@@ -51,7 +52,7 @@
 
 char StackProtector::ID = 0;
 INITIALIZE_TM_PASS(StackProtector, "stack-protector", "Insert stack protectors",
-                false, true)
+                   false, true)
 
 FunctionPass *llvm::createStackProtectorPass(const TargetMachine *TM) {
   return new StackProtector(TM);
@@ -223,6 +224,8 @@
     return false;
 
   if (F->hasFnAttribute(Attribute::StackProtectReq)) {
+    F->getContext().diagnose(
+        DiagnosticInfoSSP(*F, DiagnosticInfoSSP::SSPReason::Attribute));
     NeedsProtector = true;
     Strong = true; // Use the same heuristic as strong to determine SSPLayout
   } else if (F->hasFnAttribute(Attribute::StackProtectStrong))
@@ -241,15 +244,21 @@
               // A call to alloca with size >= SSPBufferSize requires
               // stack protectors.
               Layout.insert(std::make_pair(AI, SSPLK_LargeArray));
+              F->getContext().diagnose(
+                  DiagnosticInfoSSP(*F, DiagnosticInfoSSP::SSPReason::Alloca));
               NeedsProtector = true;
             } else if (Strong) {
               // Require protectors for all alloca calls in strong mode.
               Layout.insert(std::make_pair(AI, SSPLK_SmallArray));
+              F->getContext().diagnose(
+                  DiagnosticInfoSSP(*F, DiagnosticInfoSSP::SSPReason::Alloca));
               NeedsProtector = true;
             }
           } else {
             // A call to alloca with a variable size requires protectors.
             Layout.insert(std::make_pair(AI, SSPLK_LargeArray));
+            F->getContext().diagnose(
+                DiagnosticInfoSSP(*F, DiagnosticInfoSSP::SSPReason::Alloca));
             NeedsProtector = true;
           }
           continue;
@@ -259,6 +268,8 @@
         if (ContainsProtectableArray(AI->getAllocatedType(), IsLarge, Strong)) {
           Layout.insert(std::make_pair(AI, IsLarge ? SSPLK_LargeArray
                                                    : SSPLK_SmallArray));
+          F->getContext().diagnose(DiagnosticInfoSSP(
+              *F, DiagnosticInfoSSP::SSPReason::BufferOrStruct));
           NeedsProtector = true;
           continue;
         }
@@ -266,6 +277,8 @@
         if (Strong && HasAddressTaken(AI)) {
           ++NumAddrTaken;
           Layout.insert(std::make_pair(AI, SSPLK_AddrOf));
+          F->getContext().diagnose(DiagnosticInfoSSP(
+              *F, DiagnosticInfoSSP::SSPReason::AddressTaken));
           NeedsProtector = true;
         }
       }
@@ -464,3 +477,33 @@
 bool StackProtector::shouldEmitSDCheck(const BasicBlock &BB) const {
   return HasPrologue && !HasIRCheck && dyn_cast<ReturnInst>(BB.getTerminator());
 }
+
+void DiagnosticInfoSSP::print(DiagnosticPrinter &DP) const {
+  std::string Str;
+  raw_string_ostream OS(Str);
+
+  std::string ReasonStr;
+  switch (Reason())
+  {
+  case Unknown:
+      ReasonStr = "an unknown reason";
+      break;
+  case Alloca:
+      ReasonStr = "a call to alloca";
+      break;
+  case BufferOrStruct:
+      ReasonStr = "a stack allocated buffer or struct containing a buffer";
+      break;
+  case AddressTaken:
+      ReasonStr = "the address of a local variable being taken";
+      break;
+  case Attribute:
+      ReasonStr = "a function attribute or use of -fstack-protector-all";
+      break;
+  }
+
+  OS << getLocationStr() << ": SSP applied to function " << Func.getName()
+     << " due to " << ReasonStr << '\n';
+  OS.flush();
+  DP << Str;
+}