Don't call memmove when there's nothing to move. Fixes PR#27978.
git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@271794 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/include/fstream b/include/fstream
index d51da45..3cb3b13 100644
--- a/include/fstream
+++ b/include/fstream
@@ -606,7 +606,9 @@
}
else
{
- memmove(__extbuf_, __extbufnext_, __extbufend_ - __extbufnext_);
+ _LIBCPP_ASSERT ( !(__extbufnext_ == NULL && (__extbufend_ != __extbufnext_)), "underflow moving from NULL" );
+ if (__extbufend_ != __extbufnext_)
+ memmove(__extbuf_, __extbufnext_, __extbufend_ - __extbufnext_);
__extbufnext_ = __extbuf_ + (__extbufend_ - __extbufnext_);
__extbufend_ = __extbuf_ + (__extbuf_ == __extbuf_min_ ? sizeof(__extbuf_min_) : __ebs_);
size_t __nmemb = _VSTD::min(static_cast<size_t>(__ibs_ - __unget_sz),