Index: llvm/lib/Transforms/IPO/PassManagerBuilder.cpp
===================================================================
--- llvm/lib/Transforms/IPO/PassManagerBuilder.cpp
+++ llvm/lib/Transforms/IPO/PassManagerBuilder.cpp
@@ -405,6 +405,9 @@
     else if (!GlobalExtensions->empty() || !Extensions.empty())
       MPM.add(createBarrierNoopPass());
 
+    // Clang may generate unreachable call-graphs, let's prune it.
+    MPM.add(createGlobalDCEPass());
+
     if (PrepareForThinLTO)
       // Rename anon globals to be able to export them in the summary.
       MPM.add(createNameAnonGlobalPass());
Index: llvm/test/Other/GlobalDCE_at_O0.ll
===================================================================
--- /dev/null
+++ llvm/test/Other/GlobalDCE_at_O0.ll
@@ -0,0 +1,7 @@
+; RUN: opt < %s -O0 -S | FileCheck %s
+
+; CHECK-NOT: @test1
+
+define internal i32 @test1() {
+	ret i32 42
+}