When filling a vector<bool> with stuff, initialize the last word of the storage that you're touching. Otherwise, when we lay down the bits with operator&=, we get UB from reading uninitialized memory. Fixes Bug 39354. Thanks to David Wagner for the bug report.

llvm-svn: 345067

1 files changed, 4 insertions, 0 deletions

diff --git a/libcxx/include/vector b/libcxx/include/vector
index de7de093d58..8ac7576ae7f 100644
--- a/libcxx/include/vector
+++ b/libcxx/include/vector
@@ -2606,6 +2606,8 @@ vector<bool, _Allocator>::__construct_at_end(size_type __n, bool __x)
 {
     size_type __old_size = this->__size_;
     this->__size_ += __n;
+    if (__old_size == 0 || (__old_size / __bits_per_word) != (this->__size_ / __bits_per_word))
+    	this->__begin_[this->__size_ / __bits_per_word] = __storage_type(0);
     _VSTD::fill_n(__make_iter(__old_size), __n, __x);
 }
 
@@ -2620,6 +2622,8 @@ vector<bool, _Allocator>::__construct_at_end(_ForwardIterator __first, _ForwardI
 {
     size_type __old_size = this->__size_;
     this->__size_ += _VSTD::distance(__first, __last);
+    if (__old_size == 0 || (__old_size / __bits_per_word) != (this->__size_ / __bits_per_word))
+    	this->__begin_[this->__size_ / __bits_per_word] = __storage_type(0);
     _VSTD::copy(__first, __last, __make_iter(__old_size));
 }