Index: lib/Transforms/IPO/Inliner.cpp
===================================================================
--- lib/Transforms/IPO/Inliner.cpp
+++ lib/Transforms/IPO/Inliner.cpp
@@ -113,6 +113,11 @@
                           "printing of statistics for each inlined function")),
     cl::Hidden, cl::desc("Enable inliner stats for imported functions"));
 
+/// Flag to add inline messages as callsite attributes 'inline-remark'.
+static cl::opt<bool>
+    InlineRemarkAttribute("inline-remark-attribute", cl::init(false),
+                           cl::Hidden);
+
 LegacyInlinerBase::LegacyInlinerBase(char &ID) : CallGraphSCCPass(ID) {}
 
 LegacyInlinerBase::LegacyInlinerBase(char &ID, bool InsertLifetime)
@@ -388,13 +393,11 @@
   return R;
 }
 
-#ifndef NDEBUG
 static std::string inlineCostStr(const InlineCost &IC) {
   std::stringstream Remark;
   Remark << IC;
   return Remark.str();
 }
-#endif
 
 /// Return the cost only if the inliner should attempt to inline at the given
 /// CallSite. If we return the cost, we will emit an optimisation remark later
@@ -500,6 +503,13 @@
   });
 }
 
+static void setInlineRemark(CallSite &CS, StringRef message) {
+  if (InlineRemarkAttribute) {
+    Attribute attr = Attribute::get(CS->getContext(), "inline-remark", message);
+    CS.addAttribute(AttributeList::FunctionIndex, attr);
+  }
+}
+
 static bool
 inlineCallsImpl(CallGraphSCC &SCC, CallGraph &CG,
                 std::function<AssumptionCache &(Function &)> GetAssumptionCache,
@@ -549,6 +559,7 @@
           if (Callee->isDeclaration()) {
             using namespace ore;
 
+            setInlineRemark(CS, "unavailable definition");
             ORE.emit([&]() {
               return OptimizationRemarkMissed(DEBUG_TYPE, "NoDefinition", &I)
                      << NV("Callee", Callee) << " will not be inlined into "
@@ -612,8 +623,10 @@
         // infinitely inline.
         InlineHistoryID = CallSites[CSi].second;
         if (InlineHistoryID != -1 &&
-            InlineHistoryIncludes(Callee, InlineHistoryID, InlineHistory))
+            InlineHistoryIncludes(Callee, InlineHistoryID, InlineHistory)) {
+          setInlineRemark(CS, "recursive");
           continue;
+        }
       }
 
       // FIXME for new PM: because of the old PM we currently generate ORE and
@@ -624,7 +637,13 @@
       Optional<InlineCost> OIC = shouldInline(CS, GetInlineCost, ORE);
       // If the policy determines that we should inline this function,
       // delete the call instead.
-      if (!OIC || !*OIC) {
+      if (!OIC.hasValue()) {
+        setInlineRemark(CS, "deferred");
+        continue;
+      }
+
+      if (!OIC.getValue()) {
+        setInlineRemark(CS, inlineCostStr(*OIC)); // OIC explains
         continue;
       }
 
@@ -635,6 +654,7 @@
       if (IsTriviallyDead) {
         LLVM_DEBUG(dbgs() << "    -> Deleting dead call: " << *Instr << "\n");
         // Update the call graph by deleting the edge from Callee to Caller.
+        setInlineRemark(CS, "trivially dead");
         CG[Caller]->removeCallEdgeFor(CS);
         Instr->eraseFromParent();
         ++NumCallsDeleted;
@@ -650,6 +670,7 @@
             CS, InlineInfo, InlinedArrayAllocas, InlineHistoryID,
             InsertLifetime, AARGetter, ImportedFunctionsStats);
         if (!IR) {
+          setInlineRemark(CS, std::string(IR) + "; " + inlineCostStr(*OIC));
           ORE.emit([&]() {
             return OptimizationRemarkMissed(DEBUG_TYPE, "NotInlined", DLoc,
                                             Block)
@@ -892,6 +913,7 @@
             Calls.push_back({CS, -1});
           else if (!isa<IntrinsicInst>(I)) {
             using namespace ore;
+            setInlineRemark(CS, "unavailable definition");
             ORE.emit([&]() {
               return OptimizationRemarkMissed(DEBUG_TYPE, "NoDefinition", &I)
                      << NV("Callee", Callee) << " will not be inlined into "
@@ -935,8 +957,10 @@
     LazyCallGraph::Node &N = *CG.lookup(F);
     if (CG.lookupSCC(N) != C)
       continue;
-    if (F.hasFnAttribute(Attribute::OptimizeNone))
+    if (F.hasFnAttribute(Attribute::OptimizeNone)) {
+      setInlineRemark(Calls[i].first, "optnone attribute");
       continue;
+    }
 
     LLVM_DEBUG(dbgs() << "Inlining calls in: " << F.getName() << "\n");
 
@@ -980,8 +1004,10 @@
       Function &Callee = *CS.getCalledFunction();
 
       if (InlineHistoryID != -1 &&
-          InlineHistoryIncludes(&Callee, InlineHistoryID, InlineHistory))
+          InlineHistoryIncludes(&Callee, InlineHistoryID, InlineHistory)) {
+        setInlineRemark(CS, "recursive");
         continue;
+      }
 
       // Check if this inlining may repeat breaking an SCC apart that has
       // already been split once before. In that case, inlining here may
@@ -993,13 +1019,21 @@
         LLVM_DEBUG(dbgs() << "Skipping inlining internal SCC edge from a node "
                              "previously split out of this SCC by inlining: "
                           << F.getName() << " -> " << Callee.getName() << "\n");
+        setInlineRemark(CS, "recursive SCC split");
         continue;
       }
 
       Optional<InlineCost> OIC = shouldInline(CS, GetInlineCost, ORE);
       // Check whether we want to inline this callsite.
-      if (!OIC || !*OIC)
+      if (!OIC.hasValue()) {
+        setInlineRemark(CS, "deferred");
         continue;
+      }
+
+      if (!OIC.getValue()) {
+        setInlineRemark(CS, inlineCostStr(*OIC)); // OIC explains
+        continue;
+      }
 
       // Setup the data structure used to plumb customization into the
       // `InlineFunction` routine.
@@ -1016,6 +1050,7 @@
 
       InlineResult IR = InlineFunction(CS, IFI);
       if (!IR) {
+        setInlineRemark(CS, std::string(IR.message) + "; " + inlineCostStr(*OIC));
         ORE.emit([&]() {
           return OptimizationRemarkMissed(DEBUG_TYPE, "NotInlined", DLoc, Block)
                  << NV("Callee", &Callee) << " will not be inlined into "
Index: test/Transforms/Inline/inline-remark.ll
===================================================================
--- test/Transforms/Inline/inline-remark.ll
+++ test/Transforms/Inline/inline-remark.ll
@@ -0,0 +1,33 @@
+; RUN: opt < %s -inline                 -inline-remark-attribute --inline-threshold=-2 -S | FileCheck %s
+
+; Test that the inliner adds inline remark attributes to non-inlined callsites.
+
+define void @foo() {
+  call void @bar(i1 true)
+  ret void
+}
+
+define void @bar(i1 %p) {
+  br i1 %p, label %bb1, label %bb2
+
+bb1:
+  call void @foo()
+  ret void
+
+bb2:
+  call void @bar(i1 true)
+  ret void
+}
+
+;; Test 1 - Correctly handle phis in outer landing pads.
+define void @test1() {
+; CHECK-LABEL: @test1
+; CHECK-NEXT: call void @bar(i1 true) [[ATTR1:#[0-9]+]]
+; CHECK-NEXT: call void @bar(i1 false) [[ATTR2:#[0-9]+]]
+  call void @bar(i1 true)
+  call void @bar(i1 false)
+  ret void
+}
+
+; CHECK: attributes [[ATTR1]] = { "inline-remark"="(cost=-5, threshold=-6)" }
+; CHECK: attributes [[ATTR2]] = { "inline-remark"="(cost=never): recursive" }