Renable LLVM's MergeFunctions pass

rdar://20920907

Swift SVN r32421

Author: aschwaighofer

lib/IRGen/IRGen.cpp

@@ -149,6 +149,7 @@ static bool performLLVM(IRGenOptions &Opts, DiagnosticEngine &Diags,
     PMBuilder.Inliner = llvm::createFunctionInliningPass(200);
     PMBuilder.SLPVectorize = false;
     PMBuilder.LoopVectorize = true;
+    PMBuilder.MergeFunctions = true;
   } else {
     PMBuilder.OptLevel = 0;
     if (!Opts.DisableLLVMOptzns)