Index: include/llvm/IR/ModuleSummaryIndex.h
===================================================================
--- include/llvm/IR/ModuleSummaryIndex.h
+++ include/llvm/IR/ModuleSummaryIndex.h
@@ -659,7 +659,10 @@
         continue; // skip over non-root nodes
       Edges.push_back(std::make_pair(P.first, CalleeInfo{}));
     }
-    assert(Edges.size() && "Couldn't find any roots in index callgraph!");
+    if (Edges.empty()) {
+      // Failed to find root - return an empty node
+      return FunctionSummary::makeDummyFunctionSummary({});
+    }
     auto CallGraphRoot = FunctionSummary::makeDummyFunctionSummary(Edges);
     return CallGraphRoot;
   }
Index: include/llvm/Transforms/IPO/FunctionImport.h
===================================================================
--- include/llvm/Transforms/IPO/FunctionImport.h
+++ include/llvm/Transforms/IPO/FunctionImport.h
@@ -102,6 +102,15 @@
     ModuleSummaryIndex &Index,
     const DenseSet<GlobalValue::GUID> &GUIDPreservedSymbols);
 
+/// Propagate function attributes for function summaries along the index's
+/// callgraph during thinlink
+bool propagateFunctionAttrs(ModuleSummaryIndex &Index);
+
+/// Inserts the FunctionAttr flags from the Index (ReadNone, ReadOnly,
+/// NoRecurse, NoAlias) into \p TheModule.
+void thinLTOInsertFunctionAttrsForModule(Module &TheModule,
+                                         const GVSummaryMapTy &DefinedGlobals);
+
 /// Compute the set of summaries needed for a ThinLTO backend compilation of
 /// \p ModulePath.
 //
Index: lib/LTO/LTO.cpp
===================================================================
--- lib/LTO/LTO.cpp
+++ lib/LTO/LTO.cpp
@@ -1052,6 +1052,7 @@
     if (!ModuleToDefinedGVSummaries.count(Mod.first))
       ModuleToDefinedGVSummaries.try_emplace(Mod.first);
 
+  propagateFunctionAttrs(ThinLTO.CombinedIndex);
   StringMap<FunctionImporter::ImportMapTy> ImportLists(
       ThinLTO.ModuleMap.size());
   StringMap<FunctionImporter::ExportSetTy> ExportLists(
Index: lib/LTO/LTOBackend.cpp
===================================================================
--- lib/LTO/LTOBackend.cpp
+++ lib/LTO/LTOBackend.cpp
@@ -414,6 +414,7 @@
 
   renameModuleForThinLTO(Mod, CombinedIndex);
 
+  thinLTOInsertFunctionAttrsForModule(Mod, DefinedGlobals);
   thinLTOResolveWeakForLinkerModule(Mod, DefinedGlobals);
 
   if (Conf.PostPromoteModuleHook && !Conf.PostPromoteModuleHook(Task, Mod))
Index: lib/Transforms/IPO/FunctionImport.cpp
===================================================================
--- lib/Transforms/IPO/FunctionImport.cpp
+++ lib/Transforms/IPO/FunctionImport.cpp
@@ -13,6 +13,7 @@
 
 #include "llvm/Transforms/IPO/FunctionImport.h"
 
+#include "llvm/ADT/SCCIterator.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/Statistic.h"
 #include "llvm/ADT/StringSet.h"
@@ -40,6 +41,8 @@
 STATISTIC(NumImportedModules, "Number of modules imported from");
 STATISTIC(NumDeadSymbols, "Number of dead stripped symbols in index");
 STATISTIC(NumLiveSymbols, "Number of live symbols in index");
+STATISTIC(NumNoRecurse,
+          "Number of of functions marked norecurse from summary propagation");
 
 /// Limit on instruction count of imported functions.
 static cl::opt<unsigned> ImportInstrLimit(
@@ -410,6 +413,62 @@
 #endif
 }
 
+/// Propagates NoRecurse attributes throughout
+/// the Index (uses same method as FunctionAttrs pass)
+bool llvm::propagateFunctionAttrs(ModuleSummaryIndex &Index) {
+  // TODO: implement addNoAliasAttrs once
+  // there's more information about the return type in the summary
+
+  auto addNoRecurseAttrs = [](std::vector<ValueInfo> &SCCNodes) {
+    if (SCCNodes.size() != 1)
+      return false;
+
+    ValueInfo V = SCCNodes.front();
+
+    // Bail if we don't have a FunctionSummary to work with
+    if (!V.getSummaryList().size())
+      return false;
+
+    FunctionSummary *F =
+        cast<FunctionSummary>(V.getSummaryList().front().get());
+
+    // The dummy root node has guid of 0, so skip it
+    if (V.getGUID() == 0 || F->fflags().NoRecurse)
+      return false;
+
+    bool calleesMightRecurse = std::any_of(
+        F->calls().begin(), F->calls().end(),
+        [&F](const FunctionSummary::EdgeTy &E) {
+          if (E.first.getGUID() == 0 || !E.first.getSummaryList().size())
+            return true; // might recurse - we can't reason about external
+                         // functions
+          FunctionSummary *CFS =
+              cast<FunctionSummary>(E.first.getSummaryList().front().get());
+          return !CFS->fflags().NoRecurse;
+        });
+
+    if (calleesMightRecurse)
+      return false;
+
+    if (!F->fflags().NoRecurse) {
+      F->fflags().NoRecurse = true;
+      NumNoRecurse++;
+      return true;
+    }
+    return false;
+  };
+
+  bool Changed = false;
+
+  // Call propagation functions on each SCC in the Index
+  for (scc_iterator<ModuleSummaryIndex *> I = scc_begin(&Index); !I.isAtEnd();
+       ++I) {
+    std::vector<ValueInfo> Nodes(*I);
+    Changed |= addNoRecurseAttrs(Nodes);
+  }
+  return Changed;
+}
+
 void llvm::computeDeadSymbols(
     ModuleSummaryIndex &Index,
     const DenseSet<GlobalValue::GUID> &GUIDPreservedSymbols) {
@@ -514,6 +573,24 @@
   return std::error_code();
 }
 
+/// Insert function attributes in the Index back into the \p TheModule.
+void llvm::thinLTOInsertFunctionAttrsForModule(
+    Module &TheModule, const GVSummaryMapTy &DefinedGlobals) {
+  for (Function &F : TheModule) {
+    const auto &GV = DefinedGlobals.find(F.getGUID());
+    if (GV == DefinedGlobals.end())
+      return;
+
+    FunctionSummary *FS = cast<FunctionSummary>(GV->second);
+    if (FS->fflags().ReadNone)
+      F.setDoesNotAccessMemory();
+    if (FS->fflags().ReadOnly)
+      F.setOnlyReadsMemory();
+    if (FS->fflags().NoRecurse)
+      F.setDoesNotRecurse();
+  }
+}
+
 /// Fixup WeakForLinker linkages in \p TheModule based on summary analysis.
 void llvm::thinLTOResolveWeakForLinkerModule(
     Module &TheModule, const GVSummaryMapTy &DefinedGlobals) {
Index: test/ThinLTO/X86/Inputs/function-attr-prop-a.ll
===================================================================
--- /dev/null
+++ test/ThinLTO/X86/Inputs/function-attr-prop-a.ll
@@ -0,0 +1,6 @@
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+define i32 @c() norecurse {
+  ret i32 4
+}
Index: test/ThinLTO/X86/functionattr-prop.ll
===================================================================
--- /dev/null
+++ test/ThinLTO/X86/functionattr-prop.ll
@@ -0,0 +1,15 @@
+; RUN: llvm-as %s -o %t1.o
+; RUN: llvm-as %p/Inputs/function-attr-prop-a.ll -o %t2.o
+; RUN: llvm-lto2 run -o %t3.o %t2.o %t1.o -r %t2.o,c,px -r %t1.o,d,px -r %t1.o,c,l -save-temps
+; RUN: llvm-dis < %t3.o.0.4.opt.bc -o - | FileCheck %s
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+declare i32 @c()
+; CHECK: define i32 @d() {{.*}} #0
+define i32 @d() {
+  call i32 @c()
+  ret i32 1;
+}
+; CHECK: #0 = { norecurse