run mem2reg after the second jump threading pass in llvm-ld.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@52728 91177308-0d34-0410-b5e6-96231b3b80d8

tools/llvm-ld/Optimize.cpp

@@ -148,7 +148,8 @@ void Optimize(Module* M) {
     addPass(Passes, createInstructionCombiningPass());
 
     addPass(Passes, createJumpThreadingPass());        // Thread jumps.
-
+    addPass(Passes, createPromoteMemoryToRegisterPass()); // Cleanup jumpthread.
+    
     // Delete basic blocks, which optimization passes may have killed...
     addPass(Passes, createCFGSimplificationPass());