[libcxx] Avoid spurious construction of valarray elements

Summary:
Currently libc++ implements some operations on valarray by using the
resize method. This method has a parameter with a default value.
Because of this, valarray may spuriously construct and destruct
objects of valarray's element type.
    
This patch fixes this issue and adds corresponding test cases.


Reviewers: EricWF, mclow.lists

Reviewed By: mclow.lists

Subscribers: rogfer01, cfe-commits

Differential Revision: https://reviews.llvm.org/D41992

llvm-svn: 324596

1 files changed, 12 insertions, 0 deletions

diff --git a/libcxx/test/std/numerics/numarray/template.valarray/valarray.cons/default.pass.cpp b/libcxx/test/std/numerics/numarray/template.valarray/valarray.cons/default.pass.cpp
index f46e0bf28cf..9933322de96 100644
--- a/libcxx/test/std/numerics/numarray/template.valarray/valarray.cons/default.pass.cpp
+++ b/libcxx/test/std/numerics/numarray/template.valarray/valarray.cons/default.pass.cpp
@@ -16,6 +16,13 @@
 #include <valarray>
 #include <cassert>
 
+struct S {
+    S() { ctor_called = true; }
+    static bool ctor_called;
+};
+
+bool S::ctor_called = false;
+
 int main()
 {
     {
@@ -34,4 +41,9 @@ int main()
         std::valarray<std::valarray<double> > v;
         assert(v.size() == 0);
     }
+    {
+        std::valarray<S> v;
+        assert(v.size() == 0);
+        assert(!S::ctor_called);
+    }
 }