Ensure SmallVector::insert doesn't overwrite the last element in the range with the already-moved-from value

This would cause the last element in a range to be in a moved-from state
after an insert at a non-end position, losing that value entirely in the
process.

Side note: move_backward is subtle. It copies [A, B) to C-1 and down.
(the fact that it decrements both the second and third iterators before
the first movement is the subtle part... kind of surprising, anyway)

llvm-svn: 210426

2 files changed, 23 insertions, 1 deletions

diff --git a/llvm/include/llvm/ADT/SmallVector.h b/llvm/include/llvm/ADT/SmallVector.h
index dcf0354860f..29ad250010e 100644
--- a/llvm/include/llvm/ADT/SmallVector.h
+++ b/llvm/include/llvm/ADT/SmallVector.h
@@ -488,9 +488,9 @@ public:
     }
 
     ::new ((void*) this->end()) T(::std::move(this->back()));
-    this->setEnd(this->end()+1);
     // Push everything else over.
     this->move_backward(I, this->end()-1, this->end());
+    this->setEnd(this->end()+1);
 
     // If we just moved the element we're inserting, be sure to update
     // the reference.
diff --git a/llvm/unittests/ADT/SmallVectorTest.cpp b/llvm/unittests/ADT/SmallVectorTest.cpp
index 58f55914ba5..cccf93b6bc5 100644
--- a/llvm/unittests/ADT/SmallVectorTest.cpp
+++ b/llvm/unittests/ADT/SmallVectorTest.cpp
@@ -531,4 +531,26 @@ TEST(SmallVectorCustomTest, NoAssignTest) {
   EXPECT_EQ(42, vec.pop_back_val().x);
 }
 
+struct MovedFrom {
+  bool hasValue;
+  MovedFrom() : hasValue(true) {
+  }
+  MovedFrom(MovedFrom&& m) : hasValue(m.hasValue) {
+    m.hasValue = false;
+  }
+  MovedFrom &operator=(MovedFrom&& m) {
+    hasValue = m.hasValue;
+    m.hasValue = false;
+    return *this;
+  }
+};
+
+TEST(SmallVectorTest, MidInsert) {
+  SmallVector<MovedFrom, 3> v;
+  v.push_back(MovedFrom());
+  v.insert(v.begin(), MovedFrom());
+  for (MovedFrom &m : v)
+    EXPECT_TRUE(m.hasValue);
+}
+
 }