Fix a subtle issue in SmallVector. The following code did not work as expected:

  vec.insert(vec.begin(), vec[3]);
The issue was that vec[3] returns a reference into the vector, which is invalidated when insert() memmove's the elements down to make space.  The method needs to specifically detect and handle this case to correctly match std::vector's semantics.

Thanks to Howard Hinnant for clarifying the correct behavior, and explaining how std::vector solves this problem.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@134554 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 8 insertions, 1 deletions

diff --git a/include/llvm/ADT/SmallVector.h b/include/llvm/ADT/SmallVector.h
index 8b0a13d6ed..5f0a55bec4 100644
--- a/include/llvm/ADT/SmallVector.h
+++ b/include/llvm/ADT/SmallVector.h
@@ -410,7 +410,14 @@ public:
       this->setEnd(this->end()+1);
       // Push everything else over.
       std::copy_backward(I, this->end()-1, this->end());
-      *I = Elt;
+
+      // If we just moved the element we're inserting, be sure to update
+      // the reference.
+      const T *EltPtr = &Elt;
+      if (I <= EltPtr && EltPtr < this->EndX)
+        ++EltPtr;
+
+      *I = *EltPtr;
       return I;
     }
     size_t EltNo = I-this->begin();