Index: include/clang/Frontend/CompilerInstance.h
===================================================================
--- include/clang/Frontend/CompilerInstance.h
+++ include/clang/Frontend/CompilerInstance.h
@@ -161,6 +161,12 @@
   /// One or more modules failed to build.
   bool ModuleBuildFailed = false;
 
+  /// Whether we should delete VerboseOutputStream on destruction.
+  bool OwnsVerboseOutputStream = false;
+
+  /// The stream for verbose output.
+  raw_ostream *VerboseOutputStream = &llvm::errs();
+
   /// Holds information about the output file.
   ///
   /// If TempFilename is not empty we must rename it to Filename at the end.
@@ -223,9 +229,6 @@
   /// \param Act - The action to execute.
   /// \return - True on success.
   //
-  // FIXME: This function should take the stream to write any debugging /
-  // verbose output to as an argument.
-  //
   // FIXME: Eliminate the llvm_shutdown requirement, that should either be part
   // of the context or else not CompilerInstance specific.
   bool ExecuteAction(FrontendAction &Act);
@@ -356,6 +359,21 @@
   }
 
   /// }
+  /// @name VerboseOutputStream
+  /// }
+
+  /// Replace the current stream for verbose output.
+  ///
+  /// If not set, this stream defaults to \c llvm::errs().
+  void setVerboseOutputStream(raw_ostream &Value,
+                              bool OwnsOutputStream = false);
+
+  /// Get the current stream for verbose output.
+  raw_ostream &getVerboseOutputStream() {
+    return *VerboseOutputStream;
+  }
+
+  /// }
   /// @name Target Info
   /// {
 
Index: lib/Frontend/CompilerInstance.cpp
===================================================================
--- lib/Frontend/CompilerInstance.cpp
+++ lib/Frontend/CompilerInstance.cpp
@@ -70,6 +70,8 @@
 
 CompilerInstance::~CompilerInstance() {
   assert(OutputFiles.empty() && "Still output files in flight?");
+  if (OwnsVerboseOutputStream)
+    delete VerboseOutputStream;
 }
 
 void CompilerInstance::setInvocation(
@@ -88,6 +90,12 @@
   Diagnostics = Value;
 }
 
+void CompilerInstance::setVerboseOutputStream(raw_ostream &Value,
+                                              bool OwnsOutputStream) {
+  OwnsVerboseOutputStream = OwnsOutputStream;
+  VerboseOutputStream = &Value;
+}
+
 void CompilerInstance::setTarget(TargetInfo *Value) { Target = Value; }
 void CompilerInstance::setAuxTarget(TargetInfo *Value) { AuxTarget = Value; }
 
@@ -907,9 +915,7 @@
   assert(!getFrontendOpts().ShowHelp && "Client must handle '-help'!");
   assert(!getFrontendOpts().ShowVersion && "Client must handle '-version'!");
 
-  // FIXME: Take this as an argument, once all the APIs we used have moved to
-  // taking it as an input instead of hard-coding llvm::errs.
-  raw_ostream &OS = llvm::errs();
+  raw_ostream &OS = getVerboseOutputStream();
 
   if (!Act.PrepareToExecute(*this))
     return false;
Index: unittests/Frontend/OutputStreamTest.cpp
===================================================================
--- unittests/Frontend/OutputStreamTest.cpp
+++ unittests/Frontend/OutputStreamTest.cpp
@@ -10,6 +10,7 @@
 #include "clang/CodeGen/BackendUtil.h"
 #include "clang/CodeGen/CodeGenAction.h"
 #include "clang/Frontend/CompilerInstance.h"
+#include "clang/Frontend/TextDiagnosticPrinter.h"
 #include "clang/FrontendTool/Utils.h"
 #include "clang/Lex/PreprocessorOptions.h"
 #include "gtest/gtest.h"
@@ -43,4 +44,29 @@
   EXPECT_TRUE(!IRBuffer.empty());
   EXPECT_TRUE(StringRef(IRBuffer.data()).startswith("BC"));
 }
+
+TEST(FrontendOutputTests, TestVerboseOutputStream) {
+  auto Invocation = std::make_shared<CompilerInvocation>();
+  Invocation->getPreprocessorOpts().addRemappedFile(
+      "test.cc", MemoryBuffer::getMemBuffer("invalid").release());
+  Invocation->getFrontendOpts().Inputs.push_back(
+      FrontendInputFile("test.cc", InputKind::CXX));
+  Invocation->getFrontendOpts().ProgramAction = EmitBC;
+  Invocation->getTargetOpts().Triple = "i386-unknown-linux-gnu";
+  CompilerInstance Compiler;
+
+  std::string VerboseBuffer;
+  raw_string_ostream VerboseStream(VerboseBuffer);
+
+  Compiler.setInvocation(std::move(Invocation));
+  IntrusiveRefCntPtr<DiagnosticOptions> DiagOpts = new DiagnosticOptions();
+  Compiler.createDiagnostics(
+      new TextDiagnosticPrinter(llvm::nulls(), &*DiagOpts), true);
+  Compiler.setVerboseOutputStream(VerboseStream);
+
+  bool Success = ExecuteCompilerInvocation(&Compiler);
+  EXPECT_FALSE(Success);
+  EXPECT_TRUE(!VerboseStream.str().empty());
+  EXPECT_TRUE(StringRef(VerboseBuffer.data()).contains("errors generated"));
+}
 }