Index: lib/Transforms/IPO/GlobalOpt.cpp
===================================================================
--- lib/Transforms/IPO/GlobalOpt.cpp
+++ lib/Transforms/IPO/GlobalOpt.cpp
@@ -66,6 +66,7 @@
 #include "llvm/Transforms/Utils/CtorUtils.h"
 #include "llvm/Transforms/Utils/Evaluator.h"
 #include "llvm/Transforms/Utils/GlobalStatus.h"
+#include "llvm/Transforms/Utils/ModuleUtils.h"
 #include <cassert>
 #include <cstdint>
 #include <utility>
@@ -2925,10 +2926,16 @@
       if (const Comdat *C = GV.getComdat())
         if (!GV.isDiscardableIfUnused() || !GV.use_empty())
           NotDiscardableComdats.insert(C);
-    for (Function &F : M)
+    for (Function &F : M) {
+      if (F.getName() == "__stack_chk_fail" ||
+          F.getName() == "memcpy" ||
+          F.getName() == "memmove") {
+        appendToUsed(M, &F);
+      }
       if (const Comdat *C = F.getComdat())
         if (!F.isDefTriviallyDead())
           NotDiscardableComdats.insert(C);
+    }
     for (GlobalAlias &GA : M.aliases())
       if (const Comdat *C = GA.getComdat())
         if (!GA.isDiscardableIfUnused() || !GA.use_empty())
Index: test/ThinLTO/X86/Inputs/builtin-nostrip.ll
===================================================================
--- test/ThinLTO/X86/Inputs/builtin-nostrip.ll
+++ test/ThinLTO/X86/Inputs/builtin-nostrip.ll
@@ -0,0 +1,9 @@
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+
+; Called via llvm.global_ctors, should be detected as live via the
+; marking of llvm.global_ctors as a live root in the index.
+define void @boo() {
+  ret void
+}
Index: test/ThinLTO/X86/builtin-nostrip.ll
===================================================================
--- test/ThinLTO/X86/builtin-nostrip.ll
+++ test/ThinLTO/X86/builtin-nostrip.ll
@@ -0,0 +1,93 @@
+; RUN: opt -module-summary %s -o %t1.bc
+; RUN: opt -module-summary %p/Inputs/builtin-nostrip.ll -o %t2.bc
+
+; RUN: llvm-lto -exported-symbol=main -thinlto-action=run %t1.bc %t2.bc
+; RUN: llvm-nm %t1.bc.thinlto.o | FileCheck %s --check-prefix=CHECK-NM
+
+; RUN: llvm-lto2 run %t1.bc %t2.bc -o %t.out -save-temps \
+; RUN:   -r %t1.bc,main,plx \
+; RUN:   -r %t1.bc,bar,pl \
+; RUN:   -r %t1.bc,boo,l \
+; RUN:   -r %t1.bc,live_available_externally_func,l \
+; RUN:   -r %t1.bc,__stack_chk_fail,pl \
+; RUN:   -r %t1.bc,memmove,pl \
+; RUN:   -r %t1.bc,memcpy,pl \
+; RUN:   -r %t2.bc,boo,pl
+
+; The final binary should not contain any of the dead functions;
+; make sure _stack_chk_fail is there.
+; CHECK-NM-NOT: bar
+; CHECK-NM: t __stack_chk_fail
+
+; RUN: llvm-lto2 run %t1.bc %t2.bc -o %t.out -save-temps \
+; RUN:   -r %t1.bc,main,plx \
+; RUN:   -r %t1.bc,bar,pl \
+; RUN:   -r %t1.bc,boo,l \
+; RUN:   -r %t1.bc,live_available_externally_func,l \
+; RUN:   -r %t1.bc,__stack_chk_fail,pl \
+; RUN:   -r %t1.bc,memmove,pl \
+; RUN:   -r %t1.bc,memcpy,pl \
+; RUN:   -r %t2.bc,boo,pl
+
+; The final binary should not contain any of the dead functions;
+; make sure memmove and memcpy are there.
+; CHECK-NM-NOT: bar
+; CHECK-NM: t memcpy
+; CHECK-NM: t memmove
+
+; Next test the case where Inputs/builtin-nostrip.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
+; and it shouldn't be internalized.
+; RUN: opt %p/Inputs/builtin-nostrip.ll -o %t3.bc
+; RUN: llvm-lto2 run %t1.bc %t3.bc -o %t4.out -save-temps \
+; RUN:   -r %t1.bc,main,plx \
+; RUN:   -r %t1.bc,bar,pl \
+; RUN:   -r %t1.bc,boo,l \
+; RUN:   -r %t1.bc,live_available_externally_func,l \
+; RUN:   -r %t1.bc,__stack_chk_fail,pl \
+; RUN:   -r %t1.bc,memmove,pl \
+; RUN:   -r %t1.bc,memcpy,pl \
+; RUN:   -r %t3.bc,boo,pl 
+
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+
+@llvm.global_ctors = appending global [1 x { i32, void ()* }] [{ i32, void ()* } { i32 65535, void ()* @_GLOBAL__I_a }]
+
+declare void @boo()
+
+define internal void @_GLOBAL__I_a() #1 section "__TEXT,__StaticInit,regular,pure_instructions" {
+entry:
+    call void @boo()
+    ret void
+}
+
+define void @bar() {
+    ret void
+}
+
+
+define void @__stack_chk_fail() {
+    ret void
+}
+
+define void @memmove() {
+    ret void
+}
+
+define void @memcpy() {
+    ret void
+}
+
+define available_externally void @live_available_externally_func() {
+    ret void
+}
+
+define void @main() {
+    call void @bar()
+    call void @live_available_externally_func()
+    ret void
+}