processStore may delete the instruction, avoid
using dyn_cast<> on already freed memory.

llvm-svn: 50618
diff --git a/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp b/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
index d6e5f39..8036bf8 100644
--- a/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
+++ b/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
@@ -718,8 +718,7 @@
       
       if (StoreInst *SI = dyn_cast<StoreInst>(I))
         changed_function |= processStore(SI, BI);
-
-      if (MemCpyInst* M = dyn_cast<MemCpyInst>(I)) {
+      else if (MemCpyInst* M = dyn_cast<MemCpyInst>(I)) {
         changed_function |= processMemCpy(M);
       }
     }