Fix a typo that was killing GVNPRE of select instructions.

llvm-svn: 37871
diff --git a/llvm/lib/Transforms/Scalar/GVNPRE.cpp b/llvm/lib/Transforms/Scalar/GVNPRE.cpp
index 33926ea..5d52aa4 100644
--- a/llvm/lib/Transforms/Scalar/GVNPRE.cpp
+++ b/llvm/lib/Transforms/Scalar/GVNPRE.cpp
@@ -1040,7 +1040,7 @@
           stack.push_back(r);
         else if (m != 0 && isa<Instruction>(m) &&
                  visited.count(m) == 0)
-          stack.push_back(r);
+          stack.push_back(m);
         else {
           vec.push_back(e);
           visited.insert(e);