c++: -Waddress and value-dependent expr [PR105885]

We already suppress various warnings for code that would be tautological if
written directly, but not when it's the result of template substitution.  It
seems we need to do this for -Waddress as well.

	PR c++/105885

gcc/cp/ChangeLog:

	* pt.cc (tsubst_copy_and_build): Also suppress -Waddress for
	comparison of dependent operands.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp1z/constexpr-if37.C: New test.

2 files changed, 22 insertions, 0 deletions

diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index 80d2bec..4535c14 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -20438,6 +20438,7 @@ tsubst_copy_and_build (tree t,
 	warning_sentinel s2(warn_div_by_zero, was_dep);
 	warning_sentinel s3(warn_logical_op, was_dep);
 	warning_sentinel s4(warn_tautological_compare, was_dep);
+	warning_sentinel s5(warn_address, was_dep);
 
 	tree r = build_x_binary_op
 	  (input_location, TREE_CODE (t),
diff --git a/gcc/testsuite/g++.dg/cpp1z/constexpr-if37.C b/gcc/testsuite/g++.dg/cpp1z/constexpr-if37.C
new file mode 100644
index 0000000..e11e02c
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1z/constexpr-if37.C
@@ -0,0 +1,21 @@
+// PR c++/105885
+// { dg-do compile { target c++17 } }
+// { dg-additional-options -Wall }
+
+int i;
+
+template<const char* ARG = nullptr>
+void test() {
+  if constexpr(ARG == nullptr) {
+    ++i;
+  } else {
+    --i;
+  }
+}
+
+const char CONSTSTR[] = {'\n', '\t', ' ', '\0'};
+
+int main() {
+  test();
+  test<CONSTSTR>();
+}