Add testcase that we optimize away empty std::vector

[Jan Hubicka]

Hi,
with __builtin_operator_new we now can optimize away unused std::vectors.
This adds testcases mentioned in the PR.

Regtested x86_64-linux and comitted.

        PR tree-optimization/96945

gcc/testsuite/ChangeLog:

        * g++.dg/tree-ssa/pr96945.C: New test.

diff --git a/gcc/testsuite/g++.dg/tree-ssa/pr96945.C 
b/gcc/testsuite/g++.dg/tree-ssa/pr96945.C
new file mode 100644
index 00000000000..4cb234c2f71
--- /dev/null
+++ b/gcc/testsuite/g++.dg/tree-ssa/pr96945.C
@@ -0,0 +1,60 @@
+/* { dg-do compile } */
+// { dg-options "-O1 -fdump-tree-optimized -std=c++14" }
+#include <vector>
+struct c {
+    c() = default;
+    c(const c&) =default;
+    c(c&&) = default;
+};
+void foo(){
+    std::vector<c> vi = {c(),c(),c()};
+}
+
+struct c2 {
+    c2() = default;
+    c2(const c2&) =default;
+    c2(c2&&) = default;
+};
+void foo2(){
+    std::vector<c2> vi = {c2(),c2(),c2()};
+}
+
+struct c3 {
+    c3() {};
+};
+void foo3(){
+    std::vector<c3> vi = {c3(),c3(),c3()};
+}
+
+struct c4 {
+    c4() = default;
+    c4(const c4&) {};
+};
+void foo4(){
+    std::vector<c4> vi = {c4(),c4(),c4()};
+}
+
+struct c5 {
+    c5() = default;
+    c5(const c5&) {};
+    c5(c5&&) = default;
+};
+void foo5(){
+    std::vector<c5> vi = {c5(),c5(),c5()};
+}
+
+struct c6 {
+    c6() {}
+};
+void foo6(){
+    std::vector<c6> vi = {c6(),c6(),c6()};
+}
+
+struct c7 {
+    c7() = default;
+    c7(const c7&) =default;
+};
+void foo7(){
+    std::vector<c7> vi = {c7(),c7(),c7()};
+}
+// { dg-final { scan-tree-dump-not "delete" "optimized" } }