Patchwork C++ PATCH for c++/48948 (rejecting constexpr friend that takes the current class)

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Submitter Jason Merrill
Date May 12, 2011, 5:38 p.m.
Message ID <4DCC1B06.2000702@redhat.com>
Download mbox | patch
Permalink /patch/95345/
State New
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Comments

Jason Merrill - May 12, 2011, 5:38 p.m.
While thinking about this issue some more it occurred to me that this 
deferral can be problematic for constructors, since we use whether or 
not a constructor is really constexpr to decide whether or not a class 
is literal.  The rule that seems to me to make the most sense is to say 
that if we don't know yet whether a constructor is really constexpr, it 
doesn't satisfy the literal class requirement for a constexpr constructor.

Tested x86_64-pc-linux-gnu, applied to trunk.
commit 7919b46302ba6182d2dfa31d33eacbc2335de31e
Author: Jason Merrill <jason@redhat.com>
Date:   Thu May 12 12:33:08 2011 -0400

    	* cp-tree.h (DECL_DEFERRED_CONSTEXPR_CHECK): New.
    	* semantics.c (validate_constexpr_fundecl): Set it.
    	(check_deferred_constexpr_decls): Clear it.
    	(register_constexpr_fundef): Make sure it isn't set.
    	* decl.c (grok_special_member_properties): Check it.

Patch

diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h
index ec59346..bcf78f8 100644
--- a/gcc/cp/cp-tree.h
+++ b/gcc/cp/cp-tree.h
@@ -93,6 +93,7 @@  c-common.h, not after.
       TYPENAME_IS_RESOLVING_P (in TYPE_NAME_TYPE)
       LAMBDA_EXPR_DEDUCE_RETURN_TYPE_P (in LAMBDA_EXPR)
       TARGET_EXPR_DIRECT_INIT_P (in TARGET_EXPR)
+      DECL_DEFERRED_CONSTEXPR_CHECK (in FUNCTION_DECL)
    3: (TREE_REFERENCE_EXPR) (in NON_LVALUE_EXPR) (commented-out).
       ICS_BAD_FLAG (in _CONV)
       FN_TRY_BLOCK_P (in TRY_BLOCK)
@@ -2338,6 +2339,11 @@  struct GTY((variable_size)) lang_decl {
 #define DECL_DECLARED_CONSTEXPR_P(DECL) \
   DECL_LANG_FLAG_8 (VAR_OR_FUNCTION_DECL_CHECK (STRIP_TEMPLATE (DECL)))
 
+/* True if we can't tell yet whether the argument/return types of DECL
+   are literal because one is still being defined.  */
+#define DECL_DEFERRED_CONSTEXPR_CHECK(DECL) \
+  TREE_LANG_FLAG_2 (FUNCTION_DECL_CHECK (STRIP_TEMPLATE (DECL)))
+
 /* Nonzero if this DECL is the __PRETTY_FUNCTION__ variable in a
    template function.  */
 #define DECL_PRETTY_FUNCTION_P(NODE) \
diff --git a/gcc/cp/decl.c b/gcc/cp/decl.c
index 87be112..7939140 100644
--- a/gcc/cp/decl.c
+++ b/gcc/cp/decl.c
@@ -10681,6 +10681,9 @@  grok_special_member_properties (tree decl)
 	TYPE_HAS_LIST_CTOR (class_type) = 1;
 
       if (DECL_DECLARED_CONSTEXPR_P (decl)
+	  /* It doesn't count if we can't tell yet whether or not
+	     the constructor is actually constexpr.  */
+	  && !DECL_DEFERRED_CONSTEXPR_CHECK (decl)
 	  && !copy_fn_p (decl) && !move_fn_p (decl))
 	TYPE_HAS_CONSTEXPR_CTOR (class_type) = 1;
     }
diff --git a/gcc/cp/semantics.c b/gcc/cp/semantics.c
index ffabad1..f1f3121 100644
--- a/gcc/cp/semantics.c
+++ b/gcc/cp/semantics.c
@@ -5483,7 +5483,10 @@  check_deferred_constexpr_decls (void)
   deferred_constexpr_decls = NULL;
 
   FOR_EACH_VEC_ELT (tree, vec, i, fn)
-    validate_constexpr_fundecl (fn);
+    {
+      DECL_DEFERRED_CONSTEXPR_CHECK (fn) = false;
+      validate_constexpr_fundecl (fn);
+    }
 
   if (deferred_constexpr_decls == NULL)
     {
@@ -5516,6 +5519,7 @@  validate_constexpr_fundecl (tree fun)
 				 /*defer_ok=*/true);
   if (valid < 0)
     {
+      DECL_DEFERRED_CONSTEXPR_CHECK (fun) = true;
       VEC_safe_push (tree, gc, deferred_constexpr_decls, fun);
       return NULL;
     }
@@ -5764,6 +5768,9 @@  register_constexpr_fundef (tree fun, tree body)
   constexpr_fundef entry;
   constexpr_fundef **slot;
 
+  gcc_assert (DECL_DECLARED_CONSTEXPR_P (fun)
+	      && !DECL_DEFERRED_CONSTEXPR_CHECK (fun));
+
   if (DECL_CONSTRUCTOR_P (fun))
     body = build_constexpr_constructor_member_initializers
       (DECL_CONTEXT (fun), body);
diff --git a/gcc/testsuite/g++.dg/cpp0x/constexpr-incomplete2.C b/gcc/testsuite/g++.dg/cpp0x/constexpr-incomplete2.C
new file mode 100644
index 0000000..7a9a24d
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/constexpr-incomplete2.C
@@ -0,0 +1,31 @@ 
+// A constructor that might or might not be constexpr doesn't make
+// its class literal.
+// { dg-options -std=c++0x }
+
+template <class T>
+struct B
+{
+  constexpr B(T) { }
+  constexpr B() {}
+};
+
+struct A
+{
+  B<A> b;
+};
+
+constexpr A a {};
+
+template <class T>
+struct C
+{
+  constexpr C(T) { }
+  C() {}
+};
+
+struct D
+{
+  C<D> c;
+};
+
+constexpr D d {};		// { dg-error "not literal" }