c++: Reinstate check for uninitialized bases with c++ <= 17 [PR118239]

We currently accept this code with c++ <= 17 even though it's invalid
since the base is not initialized (we properly reject it with c++ >= 20)

=== cut here ===
struct NoMut1 { int a, b; };
struct NoMut3 : NoMut1 {
  constexpr NoMut3(int a, int b) {}
};
void mutable_subobjects() {
  constexpr NoMut3 nm3(1, 2);
}
=== cut here ===

This is a fallout of r0-118700-gc2b3ec18a494e3, that ignores all fields
with DECL_ARTIFICIAL in cx_check_missing_mem_inits, including those that
represent base classes, and need to be checked.

This patch makes sure that we only skip fields that have DECL_ARTIFICIAL
if they don't have DECL_FIELD_IS_BASE.

	PR c++/118239

gcc/cp/ChangeLog:

	* constexpr.cc (cx_check_missing_mem_inits): Don't skip fields
	with DECL_FIELD_IS_BASE.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp0x/constexpr-base8.C: New test.

diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc
index 41ff78bbf2b9b399a31b7bebe4a8be021a7242e1..94a468056f907b8461b6a94eab3b5c7ceeab391b 100644 (file)
--- a/gcc/cp/constexpr.cc
+++ b/gcc/cp/constexpr.cc
@@ -839,9 +839,8 @@ cx_check_missing_mem_inits (tree ctype, tree body, bool complain)
       if (i < nelts)
        {
          index = CONSTRUCTOR_ELT (body, i)->index;
-         /* Skip base and vtable inits.  */
-         if (TREE_CODE (index) != FIELD_DECL
-             || DECL_ARTIFICIAL (index))
+         /* Skip vptr adjustment represented with a COMPONENT_REF.  */
+         if (TREE_CODE (index) != FIELD_DECL)
            continue;
        }
 
@@ -852,7 +851,8 @@ cx_check_missing_mem_inits (tree ctype, tree body, bool complain)
            continue;
          if (DECL_UNNAMED_BIT_FIELD (field))
            continue;
-         if (DECL_ARTIFICIAL (field))
+         /* Artificial fields can be ignored unless they're bases.  */
+         if (DECL_ARTIFICIAL (field) && !DECL_FIELD_IS_BASE (field))
            continue;
          if (ANON_AGGR_TYPE_P (TREE_TYPE (field)))
            {

diff --git a/gcc/testsuite/g++.dg/cpp0x/constexpr-base8.C b/gcc/testsuite/g++.dg/cpp0x/constexpr-base8.C
new file mode 100644 (file)
index 0000000..ecc2869
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/constexpr-base8.C
@@ -0,0 +1,24 @@
+// PR c++/118239
+// { dg-do "compile" { target c++11 } }
+
+struct NoMut1 {
+  int a, b;
+};
+
+// Reported case.
+struct NoMut2 : NoMut1 {
+  constexpr NoMut2(int a, int b) /*: NoMut1()*/
+  {} // { dg-error "must be initialized" "" { target c++17_down } }
+};
+
+// Variant with explicit initialization of some member.
+struct NoMut3 : NoMut1 {
+  constexpr NoMut3(int a, int b) : c(0) /*, NoMut1()*/
+  {} // { dg-error "must be initialized" "" { target c++17_down } }
+  int c;
+};
+
+void mutable_subobjects() {
+  constexpr NoMut2 nm2(1, 2); // { dg-error "constant expression" }
+  constexpr NoMut3 nm3(1, 2); // { dg-error "constant expression" }
+}