PR c++/71972 - constexpr array self-modification

	* constexpr.c (cxx_eval_array_reference): Handle looking for the
	value of an element we're currently modifying.

From-SVN: r238729

diff --git a/gcc/cp/ChangeLog b/gcc/cp/ChangeLog
index b5d816de90df8b8593f4bde3d0ae065bdff7eb2a..a540d31133ba977472dd75bbc960297f747bf32c 100644 (file)
--- a/gcc/cp/ChangeLog
+++ b/gcc/cp/ChangeLog
@@ -1,3 +1,9 @@
+2016-07-25  Jason Merrill  <jason@redhat.com>
+
+       PR c++/71972
+       * constexpr.c (cxx_eval_array_reference): Handle looking for the
+       value of an element we're currently modifying.
+
 2016-07-24  Jason Merrill  <jason@redhat.com>
 
        PR c++/71515

diff --git a/gcc/cp/constexpr.c b/gcc/cp/constexpr.c
index f139260fb8b8a5b66375c6deaba6579369ec6cfa..47fb39b42430c8dfee60a93eaa33b8a52993ec03 100644 (file)
--- a/gcc/cp/constexpr.c
+++ b/gcc/cp/constexpr.c
@@ -2129,42 +2129,49 @@ cxx_eval_array_reference (const constexpr_ctx *ctx, tree t,
   else
     found = (i < len);
 
-  if (!found)
+  if (found)
     {
-      if (TREE_CODE (ary) == CONSTRUCTOR
-         && CONSTRUCTOR_NO_IMPLICIT_ZERO (ary))
+      tree r;
+      if (TREE_CODE (ary) == CONSTRUCTOR)
+       r = (*CONSTRUCTOR_ELTS (ary))[i].value;
+      else if (TREE_CODE (ary) == VECTOR_CST)
+       r = VECTOR_CST_ELT (ary, i);
+      else if (elem_nchars == 1)
+       r = build_int_cst (cv_unqualified (TREE_TYPE (TREE_TYPE (ary))),
+                          TREE_STRING_POINTER (ary)[i]);
+      else
        {
-         /* 'ary' is part of the aggregate initializer we're currently
-            building; if there's no initializer for this element yet,
-            that's an error.  */
-         if (!ctx->quiet)
-           error ("accessing uninitialized array element");
-         *non_constant_p = true;
-         return t;
+         tree type = cv_unqualified (TREE_TYPE (TREE_TYPE (ary)));
+         r = native_interpret_expr (type, (const unsigned char *)
+                                    TREE_STRING_POINTER (ary)
+                                    + i * elem_nchars, elem_nchars);
        }
+      if (r)
+       /* Don't VERIFY_CONSTANT here.  */
+       return r;
 
-      /* If it's within the array bounds but doesn't have an explicit
-        initializer, it's value-initialized.  */
-      tree val = build_value_init (elem_type, tf_warning_or_error);
-      return cxx_eval_constant_expression (ctx, val, lval, non_constant_p,
-                                          overflow_p);
+      /* Otherwise the element doesn't have a value yet.  */
     }
 
-  if (TREE_CODE (ary) == CONSTRUCTOR)
-    return (*CONSTRUCTOR_ELTS (ary))[i].value;
-  else if (TREE_CODE (ary) == VECTOR_CST)
-    return VECTOR_CST_ELT (ary, i);
-  else if (elem_nchars == 1)
-    return build_int_cst (cv_unqualified (TREE_TYPE (TREE_TYPE (ary))),
-                         TREE_STRING_POINTER (ary)[i]);
-  else
+  /* Not found.  */
+
+  if (TREE_CODE (ary) == CONSTRUCTOR
+      && CONSTRUCTOR_NO_IMPLICIT_ZERO (ary))
     {
-      tree type = cv_unqualified (TREE_TYPE (TREE_TYPE (ary)));
-      return native_interpret_expr (type, (const unsigned char *)
-                                         TREE_STRING_POINTER (ary)
-                                         + i * elem_nchars, elem_nchars);
+      /* 'ary' is part of the aggregate initializer we're currently
+        building; if there's no initializer for this element yet,
+        that's an error.  */
+      if (!ctx->quiet)
+       error ("accessing uninitialized array element");
+      *non_constant_p = true;
+      return t;
     }
-  /* Don't VERIFY_CONSTANT here.  */
+
+  /* If it's within the array bounds but doesn't have an explicit
+     initializer, it's value-initialized.  */
+  tree val = build_value_init (elem_type, tf_warning_or_error);
+  return cxx_eval_constant_expression (ctx, val, lval, non_constant_p,
+                                      overflow_p);
 }
 
 /* Subroutine of cxx_eval_constant_expression.

diff --git a/gcc/testsuite/g++.dg/cpp1y/constexpr-array5.C b/gcc/testsuite/g++.dg/cpp1y/constexpr-array5.C
new file mode 100644 (file)
index 0000000..3abdd84
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1y/constexpr-array5.C
@@ -0,0 +1,13 @@
+// PR c++/71972
+// { dg-do compile { target c++14 } }
+
+typedef int size_t;
+template <int N> struct S {
+  template <size_t M> constexpr S(const char (&)[M]) : data{} {
+    data[0] = data[0];
+  }
+  char data[N];
+};
+int main() {
+  constexpr S<1> s1("");
+}