From: Marek Polacek <polacek@redhat.com>
Date: Tue, 17 Nov 2020 00:59:35 +0000 (-0500)
Subject: c++: Reject identifier label in constexpr [PR97846]
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=6f20c42cc162ac3725584547ab4933bae4c78665;p=gcc.git

c++: Reject identifier label in constexpr [PR97846]

[dcl.constexpr]/3 says that the function-body of a constexpr function
shall not contain an identifier label, but we aren't enforcing that.

This patch implements that.  Of course, we can't reject artificial
labels.

gcc/cp/ChangeLog:

	PR c++/97846
	* constexpr.c (potential_constant_expression_1): Reject
	LABEL_EXPRs that use non-artifical LABEL_DECLs.

gcc/testsuite/ChangeLog:

	PR c++/97846
	* g++.dg/cpp1y/constexpr-label.C: New test.
---

diff --git a/gcc/cp/constexpr.c b/gcc/cp/constexpr.c
index ef37b3043a5..4513d40cda5 100644
--- a/gcc/cp/constexpr.c
+++ b/gcc/cp/constexpr.c
@@ -7502,7 +7502,6 @@ potential_constant_expression_1 (tree t, bool want_rval, bool strict, bool now,
     case OVERLOAD:
     case TEMPLATE_ID_EXPR:
     case LABEL_DECL:
-    case LABEL_EXPR:
     case CASE_LABEL_EXPR:
     case PREDICT_EXPR:
     case CONST_DECL:
@@ -8411,6 +8410,14 @@ potential_constant_expression_1 (tree t, bool want_rval, bool strict, bool now,
 	return false;
       }
 
+    case LABEL_EXPR:
+      t = LABEL_EXPR_LABEL (t);
+      if (DECL_ARTIFICIAL (t))
+	return true;
+      else if (flags & tf_error)
+	error_at (loc, "label definition is not a constant expression");
+      return false;
+
     case ANNOTATE_EXPR:
       return RECUR (TREE_OPERAND (t, 0), rval);
 
diff --git a/gcc/testsuite/g++.dg/cpp1y/constexpr-label.C b/gcc/testsuite/g++.dg/cpp1y/constexpr-label.C
new file mode 100644
index 00000000000..a2d113c186f
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1y/constexpr-label.C
@@ -0,0 +1,9 @@
+// PR c++/97846
+// { dg-do compile { target c++14 } }
+
+constexpr int
+f ()
+{
+x: // { dg-error "label definition is not a constant expression" }
+  return 42;
+}