Re-enable tail duplication pass (now with default threshold down to 1 instruction).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@51184 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/tools/opt/opt.cpp b/tools/opt/opt.cpp
index 2639a80..e3ea59e 100644
--- a/tools/opt/opt.cpp
+++ b/tools/opt/opt.cpp
@@ -264,6 +264,7 @@
     addPass(PM, createFunctionInliningPass());   // Inline small functions
   addPass(PM, createArgumentPromotionPass());    // Scalarize uninlined fn args
 
+  addPass(PM, createTailDuplicationPass());      // Simplify cfg by copying code
   addPass(PM, createSimplifyLibCallsPass());     // Library Call Optimizations
   addPass(PM, createInstructionCombiningPass()); // Cleanup for scalarrepl.
   addPass(PM, createJumpThreadingPass());        // Thread jumps.