re PR c++/81942 (ICE on empty constexpr constructor with C++14)

/cp
2017-09-05  Paolo Carlini  <paolo.carlini@oracle.com>

	PR c++/81942
	* cp-tree.h (LABEL_DECL_CDTOR): Add and document.
	* decl.c (start_preparsed_function): Set LABEL_DECL_CDTOR when
	creating cdtor_label.
	* constexpr.c (returns): Add the case of a constructor/destructor
	returning via a LABEL_DECL_CDTOR label.
	(cxx_eval_constant_expression, case [GOTO_EXPR]): Likewise.

/testsuite
2017-09-05  Paolo Carlini  <paolo.carlini@oracle.com>

	PR c++/81942
	* g++.dg/cpp1y/constexpr-return3.C: New.

From-SVN: r251714

6 files changed, 42 insertions, 3 deletions

diff --git a/gcc/cp/ChangeLog b/gcc/cp/ChangeLog
index 55cf4a0..26b51ec 100644
--- a/gcc/cp/ChangeLog
+++ b/gcc/cp/ChangeLog
@@ -1,3 +1,13 @@
+2017-09-05  Paolo Carlini  <paolo.carlini@oracle.com>
+
+	PR c++/81942
+	* cp-tree.h (LABEL_DECL_CDTOR): Add and document.
+	* decl.c (start_preparsed_function): Set LABEL_DECL_CDTOR when
+	creating cdtor_label.
+	* constexpr.c (returns): Add the case of a constructor/destructor
+	returning via a LABEL_DECL_CDTOR label.
+	(cxx_eval_constant_expression, case [GOTO_EXPR]): Likewise.
+
 2017-09-01  Nathan Sidwell  <nathan@acm.org>
 
 	* cp-tree.h (resort_type_method_vec): Move declaration to ...
diff --git a/gcc/cp/constexpr.c b/gcc/cp/constexpr.c
index f3e868c..a5692fb 100644
--- a/gcc/cp/constexpr.c
+++ b/gcc/cp/constexpr.c
@@ -3671,7 +3671,9 @@ static bool
 returns (tree *jump_target)
 {
   return *jump_target
-    && TREE_CODE (*jump_target) == RETURN_EXPR;
+    && (TREE_CODE (*jump_target) == RETURN_EXPR
+	|| (TREE_CODE (*jump_target) == LABEL_DECL
+	    && LABEL_DECL_CDTOR (*jump_target)));
 }
 
 static bool
@@ -4554,7 +4556,9 @@ cxx_eval_constant_expression (const constexpr_ctx *ctx, tree t,
 
     case GOTO_EXPR:
       *jump_target = TREE_OPERAND (t, 0);
-      gcc_assert (breaks (jump_target) || continues (jump_target));
+      gcc_assert (breaks (jump_target) || continues (jump_target)
+		  /* Allow for jumping to a cdtor_label.  */
+		  || returns (jump_target));
       break;
 
     case LOOP_EXPR:
diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h
index 432faa9..7dc20b1 100644
--- a/gcc/cp/cp-tree.h
+++ b/gcc/cp/cp-tree.h
@@ -456,6 +456,7 @@ extern GTY(()) tree cp_global_trees[CPTI_MAX];
       DECL_CONSTRAINT_VAR_P (in a PARM_DECL)
       TEMPLATE_DECL_COMPLEX_ALIAS_P (in TEMPLATE_DECL)
       DECL_INSTANTIATING_NSDMI_P (in a FIELD_DECL)
+      LABEL_DECL_CDTOR (in LABEL_DECL)
    3: DECL_IN_AGGR_P.
    4: DECL_C_BIT_FIELD (in a FIELD_DECL)
       DECL_ANON_UNION_VAR_P (in a VAR_DECL)
@@ -3833,6 +3834,11 @@ more_aggr_init_expr_args_p (const aggr_init_expr_arg_iterator *iter)
 #define LABEL_DECL_CONTINUE(NODE) \
   DECL_LANG_FLAG_1 (LABEL_DECL_CHECK (NODE))
 
+/* Nonzero if NODE is the target for genericization of 'return' stmts
+   in constructors/destructors of targetm.cxx.cdtor_returns_this targets.  */
+#define LABEL_DECL_CDTOR(NODE) \
+  DECL_LANG_FLAG_2 (LABEL_DECL_CHECK (NODE))
+
 /* True if NODE was declared with auto in its return type, but it has
    started compilation and so the return type might have been changed by
    return type deduction; its declared return type should be found in
diff --git a/gcc/cp/decl.c b/gcc/cp/decl.c
index d6b80c6..861dfcf 100644
--- a/gcc/cp/decl.c
+++ b/gcc/cp/decl.c
@@ -15072,7 +15072,10 @@ start_preparsed_function (tree decl1, tree attrs, int flags)
   if (DECL_DESTRUCTOR_P (decl1)
       || (DECL_CONSTRUCTOR_P (decl1)
 	  && targetm.cxx.cdtor_returns_this ()))
-    cdtor_label = create_artificial_label (input_location);
+    {
+      cdtor_label = create_artificial_label (input_location);
+      LABEL_DECL_CDTOR (cdtor_label) = true;
+    }
 
   start_fname_decls ();
 
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 0ef3da8..690bc5b 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,8 @@
+2017-09-05  Paolo Carlini  <paolo.carlini@oracle.com>
+
+	PR c++/81942
+	* g++.dg/cpp1y/constexpr-return3.C: New.
+
 2017-09-05  Eric Botcazou  <ebotcazou@adacore.com>
 
 	* gnat.dg/incomplete5.ad[sb]: New test.
diff --git a/gcc/testsuite/g++.dg/cpp1y/constexpr-return3.C b/gcc/testsuite/g++.dg/cpp1y/constexpr-return3.C
new file mode 100644
index 0000000..4cf4128
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1y/constexpr-return3.C
@@ -0,0 +1,11 @@
+// PR c++/81942
+// { dg-do compile { target c++14 } }
+
+class A {
+public:
+    constexpr A() {
+      return;
+    }
+};
+
+A mwi;