Index: llvm/trunk/test/Transforms/Coroutines/smoketest.ll
===================================================================
--- llvm/trunk/test/Transforms/Coroutines/smoketest.ll
+++ llvm/trunk/test/Transforms/Coroutines/smoketest.ll
@@ -1,6 +1,7 @@
 ; Test that all coroutine passes run in the correct order at all optimization
 ; levels and -disable-coroutines removes coroutine passes from the pipeline.
 ;
+; RUN: opt < %s -disable-output -enable-coroutines -debug-pass=Arguments -O0 2>&1 | FileCheck %s
 ; RUN: opt < %s -disable-output -enable-coroutines -debug-pass=Arguments -O1 2>&1 | FileCheck %s
 ; RUN: opt < %s -disable-output -enable-coroutines -debug-pass=Arguments -O2 2>&1 | FileCheck %s
 ; RUN: opt < %s -disable-output -enable-coroutines -debug-pass=Arguments -O3 2>&1 | FileCheck %s
Index: llvm/trunk/tools/opt/opt.cpp
===================================================================
--- llvm/trunk/tools/opt/opt.cpp
+++ llvm/trunk/tools/opt/opt.cpp
@@ -122,6 +122,10 @@
                  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"));
 
@@ -515,7 +519,8 @@
                                                      : 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()));
@@ -547,6 +552,11 @@
       StandardLinkOpts = false;
     }
 
+    if (OptLevelO0 && OptLevelO0.getPosition() < PassList.getPosition(i)) {
+      AddOptimizationPasses(Passes, *FPasses, TM.get(), 0, 0);
+      OptLevelO0 = false;
+    }
+
     if (OptLevelO1 && OptLevelO1.getPosition() < PassList.getPosition(i)) {
       AddOptimizationPasses(Passes, *FPasses, TM.get(), 1, 0);
       OptLevelO1 = false;
@@ -619,6 +629,9 @@
     StandardLinkOpts = false;
   }
 
+  if (OptLevelO0)
+    AddOptimizationPasses(Passes, *FPasses, TM.get(), 0, 0);
+
   if (OptLevelO1)
     AddOptimizationPasses(Passes, *FPasses, TM.get(), 1, 0);