c++: fix rejects-valid and ICE with constexpr NSDMI [PR110822]

Since r10-7718 the attached tests produce an ICE in verify_address:

  error: constant not recomputed when 'ADDR_EXPR' changed

but before that we wrongly rejected the tests with "is not a constant
expression".  This patch fixes both problems.

Since r10-7718 replace_decl_r can replace

  {._M_dataplus=&<retval>._M_local_buf, ._M_local_buf=0}

with

  {._M_dataplus=&HelloWorld._M_local_buf, ._M_local_buf=0}

The initial &<retval>._M_local_buf was not constant, but since
HelloWorld is a static VAR_DECL, the resulting &HelloWorld._M_local_buf
should have been marked as TREE_CONSTANT.  And since we're taking
its address, the whole thing should be TREE_ADDRESSABLE.

	PR c++/114913
	PR c++/110822

gcc/cp/ChangeLog:

	* constexpr.cc (replace_decl_r): If we've replaced something
	inside of an ADDR_EXPR, call cxx_mark_addressable and
	recompute_tree_invariant_for_addr_expr on the resulting ADDR_EXPR.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp0x/constexpr-nsdmi4.C: New test.
	* g++.dg/cpp0x/constexpr-nsdmi5.C: New test.

Reviewed-by: Jason Merrill <jason@redhat.com>

2 files changed, 34 insertions, 0 deletions

diff --git a/gcc/testsuite/g++.dg/cpp0x/constexpr-nsdmi4.C b/gcc/testsuite/g++.dg/cpp0x/constexpr-nsdmi4.C
new file mode 100644
index 0000000..360470d
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/constexpr-nsdmi4.C
@@ -0,0 +1,19 @@
+// PR c++/114913
+// { dg-do compile { target c++11 } }
+
+struct strt {
+  char *_M_dataplus;
+  char _M_local_buf = 0;
+  constexpr strt()
+    : _M_dataplus(&_M_local_buf) {}
+  constexpr strt(const strt &)
+    : _M_dataplus(&_M_local_buf) {}
+};
+
+constexpr strt
+f ()
+{
+  return {};
+}
+constexpr strt HelloWorld = f();
+const char *a() { return HelloWorld._M_dataplus; }
diff --git a/gcc/testsuite/g++.dg/cpp0x/constexpr-nsdmi5.C b/gcc/testsuite/g++.dg/cpp0x/constexpr-nsdmi5.C
new file mode 100644
index 0000000..0a0acaa
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/constexpr-nsdmi5.C
@@ -0,0 +1,15 @@
+// PR c++/110822
+// { dg-do compile { target c++11 } }
+
+void __ostream_insert(const char*);
+struct basic_string {
+  const char* _M_p;
+  char _M_local_buf[16] = {};
+  constexpr basic_string() : _M_p(_M_local_buf) {}
+  const char *data() const { return _M_p; }
+};
+constexpr basic_string f() { return {}; }
+constexpr basic_string text = f();
+int main() {
+  __ostream_insert(text._M_p);
+}