Index: llvm/trunk/include/llvm/IR/Function.h
===================================================================
--- llvm/trunk/include/llvm/IR/Function.h
+++ llvm/trunk/include/llvm/IR/Function.h
@@ -710,6 +710,12 @@
     return Arguments + NumArgs;
   }
 
+  Argument* getArg(unsigned i) const {
+    assert (i < NumArgs && "getArg() out of range!");
+    CheckLazyArguments();
+    return Arguments + i;
+  }
+
   iterator_range<arg_iterator> args() {
     return make_range(arg_begin(), arg_end());
   }
Index: llvm/trunk/unittests/IR/FunctionTest.cpp
===================================================================
--- llvm/trunk/unittests/IR/FunctionTest.cpp
+++ llvm/trunk/unittests/IR/FunctionTest.cpp
@@ -33,6 +33,14 @@
   // The argument list should be populated at first access.
   (void)F->arg_begin();
   EXPECT_FALSE(F->hasLazyArguments());
+
+  // Checking that getArg gets the arguments from F1 in the correct order.
+  unsigned i = 0;
+  for (Argument &A : F->args()) {
+    EXPECT_EQ(&A, F->getArg(i));
+    ++i;
+  }
+  EXPECT_FALSE(F->hasLazyArguments());
 }
 
 TEST(FunctionTest, stealArgumentListFrom) {