Index: llvm/trunk/include/llvm/IR/ModuleSummaryIndex.h
===================================================================
--- llvm/trunk/include/llvm/IR/ModuleSummaryIndex.h
+++ llvm/trunk/include/llvm/IR/ModuleSummaryIndex.h
@@ -181,6 +181,13 @@
   bool isDSOLocal() const;
 };
 
+inline raw_ostream &operator<<(raw_ostream &OS, const ValueInfo &VI) {
+  OS << VI.getGUID();
+  if (!VI.name().empty())
+    OS << " (" << VI.name() << ")";
+  return OS;
+}
+
 inline bool operator==(const ValueInfo &A, const ValueInfo &B) {
   assert(A.getRef() && B.getRef() &&
          "Need ValueInfo with non-null Ref for comparison");
Index: llvm/trunk/lib/Transforms/IPO/FunctionImport.cpp
===================================================================
--- llvm/trunk/lib/Transforms/IPO/FunctionImport.cpp
+++ llvm/trunk/lib/Transforms/IPO/FunctionImport.cpp
@@ -254,7 +254,7 @@
       continue;
     }
 
-    LLVM_DEBUG(dbgs() << " ref -> " << VI.getGUID() << "\n");
+    LLVM_DEBUG(dbgs() << " ref -> " << VI << "\n");
 
     for (auto &RefSummary : VI.getSummaryList())
       if (RefSummary->getSummaryKind() == GlobalValueSummary::GlobalVarKind &&
@@ -284,8 +284,8 @@
   static int ImportCount = 0;
   for (auto &Edge : Summary.calls()) {
     ValueInfo VI = Edge.first;
-    LLVM_DEBUG(dbgs() << " edge -> " << VI.getGUID()
-                      << " Threshold:" << Threshold << "\n");
+    LLVM_DEBUG(dbgs() << " edge -> " << VI << " Threshold:" << Threshold
+                      << "\n");
 
     if (ImportCutoff >= 0 && ImportCount >= ImportCutoff) {
       LLVM_DEBUG(dbgs() << "ignored! import-cutoff value of " << ImportCutoff
@@ -399,8 +399,13 @@
   // Populate the worklist with the import for the functions in the current
   // module
   for (auto &GVSummary : DefinedGVSummaries) {
+#ifndef NDEBUG
+    // FIXME: Change the GVSummaryMapTy to hold ValueInfo instead of GUID
+    // so this map look up (and possibly others) can be avoided.
+    auto VI = Index.getValueInfo(GVSummary.first);
+#endif
     if (!Index.isGlobalValueLive(GVSummary.second)) {
-      LLVM_DEBUG(dbgs() << "Ignores Dead GUID: " << GVSummary.first << "\n");
+      LLVM_DEBUG(dbgs() << "Ignores Dead GUID: " << VI << "\n");
       continue;
     }
     auto *FuncSummary =
@@ -408,7 +413,7 @@
     if (!FuncSummary)
       // Skip import for global variables
       continue;
-    LLVM_DEBUG(dbgs() << "Initialize import for " << GVSummary.first << "\n");
+    LLVM_DEBUG(dbgs() << "Initialize import for " << VI << "\n");
     computeImportForFunction(*FuncSummary, Index, ImportInstrLimit,
                              DefinedGVSummaries, Worklist, ImportList,
                              ExportLists);
@@ -600,14 +605,16 @@
   }
 
   // Add values flagged in the index as live roots to the worklist.
-  for (const auto &Entry : Index)
+  for (const auto &Entry : Index) {
+    auto VI = Index.getValueInfo(Entry);
     for (auto &S : Entry.second.SummaryList)
       if (S->isLive()) {
-        LLVM_DEBUG(dbgs() << "Live root: " << Entry.first << "\n");
-        Worklist.push_back(ValueInfo(/*IsAnalysis=*/false, &Entry));
+        LLVM_DEBUG(dbgs() << "Live root: " << VI << "\n");
+        Worklist.push_back(VI);
         ++LiveSymbols;
         break;
       }
+  }
 
   // Make value live and add it to the worklist if it was not live before.
   auto visit = [&](ValueInfo VI) {
Index: llvm/trunk/test/ThinLTO/X86/Inputs/funcimport-debug.ll
===================================================================
--- llvm/trunk/test/ThinLTO/X86/Inputs/funcimport-debug.ll
+++ llvm/trunk/test/ThinLTO/X86/Inputs/funcimport-debug.ll
@@ -0,0 +1,10 @@
+target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-apple-macosx10.11.0"
+
+
+define void @foo() #0 {
+entry:
+  ret void
+}
+
+@baz = constant i32 10, align 4
Index: llvm/trunk/test/ThinLTO/X86/deadstrip.ll
===================================================================
--- llvm/trunk/test/ThinLTO/X86/deadstrip.ll
+++ llvm/trunk/test/ThinLTO/X86/deadstrip.ll
@@ -1,3 +1,6 @@
+; Require asserts for -debug-only
+; REQUIRES: asserts
+
 ; RUN: opt -module-summary %s -o %t1.bc
 ; RUN: opt -module-summary %p/Inputs/deadstrip.ll -o %t2.bc
 ; RUN: llvm-lto -thinlto-action=thinlink -o %t.index.bc %t1.bc %t2.bc
@@ -18,7 +21,9 @@
 ; RUN:   -r %t2.bc,_baz,pl \
 ; RUN:   -r %t2.bc,_boo,pl \
 ; RUN:   -r %t2.bc,_dead_func,l \
-; RUN:   -r %t2.bc,_another_dead_func,pl
+; RUN:   -r %t2.bc,_another_dead_func,pl \
+; RUN:   -thinlto-threads=1 \
+; RUN:	 -debug-only=function-import 2>&1 | FileCheck %s --check-prefix=DEBUG
 ; RUN: llvm-dis < %t.out.1.3.import.bc | FileCheck %s --check-prefix=LTO2
 ; RUN: llvm-dis < %t.out.2.3.import.bc | FileCheck %s --check-prefix=LTO2-CHECK2
 ; RUN: llvm-nm %t.out.1 | FileCheck %s --check-prefix=CHECK2-NM
@@ -71,6 +76,13 @@
 ; CHECK-NM-NOT: bar
 ; CHECK-NM-NOT: dead
 
+; DEBUG: Live root: 2412314959268824392 (llvm.global_ctors)
+; DEBUG: Live root: 15822663052811949562 (main)
+; DEBUG: Ignores Dead GUID: 7342339837106705152 (dead_func)
+; DEBUG: Ignores Dead GUID: 7546896869197086323 (baz)
+; DEBUG: Initialize import for 15611644523426561710 (boo)
+; DEBUG: Ignores Dead GUID: 2384416018110111308 (another_dead_func)
+
 ; Next test the case where Inputs/deadstrip.ll does not get a module index,
 ; which will cause it to be handled by regular LTO in the new LTO API.
 ; In that case there are uses of @dead_func in the regular LTO partition
Index: llvm/trunk/test/ThinLTO/X86/funcimport-debug.ll
===================================================================
--- llvm/trunk/test/ThinLTO/X86/funcimport-debug.ll
+++ llvm/trunk/test/ThinLTO/X86/funcimport-debug.ll
@@ -0,0 +1,35 @@
+; Test of function importing debug messages
+
+; Require asserts for -debug-only
+; REQUIRES: asserts
+
+; Do setup work for all below tests: generate bitcode and combined index
+; RUN: opt -module-summary %s -o %t1.bc
+; RUN: opt -module-summary %p/Inputs/funcimport-debug.ll -o %t2.bc
+
+; RUN: llvm-lto2 run %t1.bc %t2.bc -o %t.o -save-temps \
+; RUN:     -r=%t1.bc,_main,plx \
+; RUN:     -r=%t1.bc,_foo,l \
+; RUN:     -r=%t1.bc,_baz,l \
+; RUN:     -r=%t2.bc,_foo,plx \
+; RUN:     -r=%t2.bc,_baz,plx \
+; RUN:     -thinlto-threads=1 \
+; RUN:     -debug-only=function-import 2>&1 | FileCheck %s
+
+; CHECK-DAG: Initialize import for 6699318081062747564 (foo)
+; CHECK-DAG: Initialize import for 15822663052811949562 (main)
+; CHECK-DAG: ref -> 7546896869197086323 (baz)
+; CHECK-DAG: edge -> 6699318081062747564 (foo) Threshold:100
+
+target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-apple-macosx10.11.0"
+
+define i32 @main() #0 {
+entry:
+  call void (...) @foo()
+  %0 = load i32, i32* @baz, align 4
+  ret i32 %0
+}
+
+declare void @foo(...) #1
+@baz = external global i32