SmallVector::erase: Assert that iterators are actually inside the vector.

The rationale here is that it's hard to write loops containing vector erases and
it only shows up if the vector contains non-trivial objects leading to crashes
when forming them out of garbage memory.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@160854 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/ADT/SmallVector.h

@@ -463,6 +463,7 @@ public:
   }
 
   iterator erase(iterator I) {
+    assert(I >= this->begin() && I < this->end() && "Iterator out of bounds");
     iterator N = I;
     // Shift all elts down one.
     this->move(I+1, this->end(), I);
@@ -472,6 +473,8 @@ public:
   }
 
   iterator erase(iterator S, iterator E) {
+    assert(S >= this->begin() && S <= E && E <= this->end() &&
+           "Iterator range out of bounds");
     iterator N = S;
     // Shift all elts down.
     iterator I = this->move(E, this->end(), S);