Index: lib/Transforms/IPO/PassManagerBuilder.cpp
===================================================================
--- lib/Transforms/IPO/PassManagerBuilder.cpp
+++ lib/Transforms/IPO/PassManagerBuilder.cpp
@@ -176,6 +176,7 @@
   // if enabled, the function merging pass.
   if (OptLevel == 0) {
     if (Inliner) {
+      MPM.add(createGlobalDCEPass());         // Remove dead fns and globals.
       MPM.add(Inliner);
       Inliner = nullptr;
     }
@@ -217,6 +218,7 @@
   if (!DisableUnitAtATime)
     MPM.add(createPruneEHPass());             // Remove dead EH info
   if (Inliner) {
+    MPM.add(createGlobalDCEPass());         // Remove dead fns and globals.
     MPM.add(Inliner);
     Inliner = nullptr;
   }
@@ -453,6 +455,7 @@
   // Inline small functions
   bool RunInliner = Inliner;
   if (RunInliner) {
+    PM.add(createGlobalDCEPass());         // Remove dead fns and globals.
     PM.add(Inliner);
     Inliner = nullptr;
   }
Index: test/Transforms/Inline/always-inline-O0.ll
===================================================================
--- test/Transforms/Inline/always-inline-O0.ll
+++ test/Transforms/Inline/always-inline-O0.ll
@@ -0,0 +1,19 @@
+; RUN: opt < %s -O0 -S | FileCheck %s
+; CHECK-NOT: call{{.*}}AAA
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-linux-gnu"
+
+define void @AAA() alwaysinline {
+  ret void
+}
+
+define internal void @BBB() {
+  call void @CCC()
+  call void @AAA()
+  ret void
+}
+
+define internal void @CCC() {
+  call void @AAA()
+  ret void
+}
Index: test/Transforms/Inline/always-inline-O1.ll
===================================================================
--- test/Transforms/Inline/always-inline-O1.ll
+++ test/Transforms/Inline/always-inline-O1.ll
@@ -0,0 +1,40 @@
+; RUN: opt < %s -O1 -S | FileCheck %s
+; RUN: opt < %s -O2 -S | FileCheck %s
+; RUN: opt < %s -O3 -S | FileCheck %s
+; CHECK-NOT: call{{.*}}BBB
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+declare void @AAA()
+
+define void @BBB() alwaysinline {
+entry:
+  call void @AAA()
+  ret void
+}
+
+define internal void @CCC()  {
+entry:
+  call void @BBB()
+  ret void
+}
+
+define void @DDD(i8* %x) {
+entry:
+  %a = load i8, i8* %x, align 4
+  %cmpa = icmp ne i8 %a, 1
+  br i1 %cmpa, label %return, label %if.end
+
+if.end:
+  %b = load i8, i8* %x, align 4
+  %cmpb = icmp eq i8 %b, 1
+  br i1 %cmpb, label %return, label %if.end.2
+
+if.end.2:
+  call void @CCC()
+  br label %return
+
+return:
+  ret void
+}
Index: tools/opt/opt.cpp
===================================================================
--- tools/opt/opt.cpp
+++ tools/opt/opt.cpp
@@ -116,6 +116,10 @@
                  cl::desc("Include the standard link time optimizations"));
 
 static cl::opt<bool>
+OptLevelO0("O0",
+           cl::desc("Optimization level 0. Similar to clang -O0"));
+
+static cl::opt<bool>
 OptLevelO1("O1",
            cl::desc("Optimization level 1. Similar to clang -O1"));
 
@@ -453,7 +457,7 @@
                                                      : TargetIRAnalysis()));
 
   std::unique_ptr<legacy::FunctionPassManager> FPasses;
-  if (OptLevelO1 || OptLevelO2 || OptLevelOs || OptLevelOz || OptLevelO3) {
+  if (OptLevelO0 || OptLevelO1 || OptLevelO2 || OptLevelOs || OptLevelOz || OptLevelO3) {
     FPasses.reset(new legacy::FunctionPassManager(M.get()));
     FPasses->add(createTargetTransformInfoWrapperPass(
         TM ? TM->getTargetIRAnalysis() : TargetIRAnalysis()));
@@ -485,6 +489,11 @@
       StandardLinkOpts = false;
     }
 
+    if (OptLevelO0 && OptLevelO0.getPosition() < PassList.getPosition(i)) {
+      AddOptimizationPasses(Passes, *FPasses, 0, 0);
+      OptLevelO0 = false;
+    }
+
     if (OptLevelO1 && OptLevelO1.getPosition() < PassList.getPosition(i)) {
       AddOptimizationPasses(Passes, *FPasses, 1, 0);
       OptLevelO1 = false;
@@ -557,6 +566,9 @@
     StandardLinkOpts = false;
   }
 
+  if (OptLevelO0)
+    AddOptimizationPasses(Passes, *FPasses, 0, 0);
+
   if (OptLevelO1)
     AddOptimizationPasses(Passes, *FPasses, 1, 0);
 
@@ -572,7 +584,7 @@
   if (OptLevelO3)
     AddOptimizationPasses(Passes, *FPasses, 3, 0);
 
-  if (OptLevelO1 || OptLevelO2 || OptLevelOs || OptLevelOz || OptLevelO3) {
+  if (OptLevelO0 || OptLevelO1 || OptLevelO2 || OptLevelOs || OptLevelOz || OptLevelO3) {
     FPasses->doInitialization();
     for (Function &F : *M)
       FPasses->run(F);