re PR c++/65398 ([C++11] GCC rejects constexpr variable definitions with valid initialization)

	PR c++/65398
	* constexpr.c (cxx_fold_indirect_ref): Don't perform the
	 *(&A[i] p+ j) => A[i + j] transformation here.
	(cxx_eval_pointer_plus_expression): New function.
	(cxx_eval_constant_expression): Use it here.

	* g++.dg/cpp0x/pr65398-2.C: New test.

From-SVN: r221777

4 files changed, 102 insertions, 21 deletions

diff --git a/gcc/cp/ChangeLog b/gcc/cp/ChangeLog
index a9f872d..ec35f22 100644
--- a/gcc/cp/ChangeLog
+++ b/gcc/cp/ChangeLog
@@ -1,3 +1,11 @@
+2015-03-30  Marek Polacek  <polacek@redhat.com>
+
+	PR c++/65398
+	* constexpr.c (cxx_fold_indirect_ref): Don't perform the
+	 *(&A[i] p+ j) => A[i + j] transformation here.
+	(cxx_eval_pointer_plus_expression): New function.
+	(cxx_eval_constant_expression): Use it here.
+
 2015-03-27  Tobias Burnus  <burnus@net-b.de>
 
 	PR c/65586
diff --git a/gcc/cp/constexpr.c b/gcc/cp/constexpr.c
index 2f09472..2100f94 100644
--- a/gcc/cp/constexpr.c
+++ b/gcc/cp/constexpr.c
@@ -2427,27 +2427,6 @@ cxx_fold_indirect_ref (location_t loc, tree type, tree op0, bool *empty_base)
 		    break;
 		  }
 	    }
-	  /* *(&A[i] p+ j) => A[i + j] */
-	  else if (TREE_CODE (op00) == ARRAY_REF
-		   && TREE_CODE (TREE_OPERAND (op00, 1)) == INTEGER_CST
-		   && TREE_CODE (op01) == INTEGER_CST)
-	    {
-	      tree t = fold_convert_loc (loc, ssizetype,
-					 TREE_OPERAND (op00, 1));
-	      tree nelts
-		= array_type_nelts_top (TREE_TYPE (TREE_OPERAND (op00, 0)));
-	      /* Don't fold an out-of-bound access.  */
-	      if (!tree_int_cst_le (t, nelts))
-		return NULL_TREE;
-	      /* Make sure to treat the second operand of POINTER_PLUS_EXPR
-		 as signed.  */
-	      op01 = fold_build2_loc (loc, EXACT_DIV_EXPR, ssizetype,
-				      cp_fold_convert (ssizetype, op01),
-				      TYPE_SIZE_UNIT (type));
-	      t = size_binop_loc (loc, PLUS_EXPR, op01, t);
-	      return build4_loc (loc, ARRAY_REF, type, TREE_OPERAND (op00, 0),
-				 t, NULL_TREE, NULL_TREE);
-	    }
 	}
     }
   /* *(foo *)fooarrptr => (*fooarrptr)[0] */
@@ -2942,6 +2921,51 @@ cxx_eval_switch_expr (const constexpr_ctx *ctx, tree t,
   return NULL_TREE;
 }
 
+/* Subroutine of cxx_eval_constant_expression.
+   Attempt to reduce a POINTER_PLUS_EXPR expression T.  */
+
+static tree
+cxx_eval_pointer_plus_expression (const constexpr_ctx *ctx, tree t,
+				  bool lval, bool *non_constant_p,
+				  bool *overflow_p)
+{
+  tree op00 = TREE_OPERAND (t, 0);
+  tree op01 = TREE_OPERAND (t, 1);
+  location_t loc = EXPR_LOCATION (t);
+
+  STRIP_NOPS (op00);
+  if (TREE_CODE (op00) != ADDR_EXPR)
+    return NULL_TREE;
+
+  op00 = TREE_OPERAND (op00, 0);
+
+  /* &A[i] p+ j => &A[i + j] */
+  if (TREE_CODE (op00) == ARRAY_REF
+      && TREE_CODE (TREE_OPERAND (op00, 1)) == INTEGER_CST
+      && TREE_CODE (op01) == INTEGER_CST)
+    {
+      tree type = TREE_TYPE (op00);
+      t = fold_convert_loc (loc, ssizetype, TREE_OPERAND (op00, 1));
+      tree nelts = array_type_nelts_top (TREE_TYPE (TREE_OPERAND (op00, 0)));
+      /* Don't fold an out-of-bound access.  */
+      if (!tree_int_cst_le (t, nelts))
+	return NULL_TREE;
+      /* Make sure to treat the second operand of POINTER_PLUS_EXPR
+	 as signed.  */
+      op01 = fold_build2_loc (loc, EXACT_DIV_EXPR, ssizetype,
+			      cp_fold_convert (ssizetype, op01),
+			      TYPE_SIZE_UNIT (type));
+      t = size_binop_loc (loc, PLUS_EXPR, op01, t);
+      t = build4_loc (loc, ARRAY_REF, type, TREE_OPERAND (op00, 0),
+		      t, NULL_TREE, NULL_TREE);
+      t = cp_build_addr_expr (t, tf_warning_or_error);
+      return cxx_eval_constant_expression (ctx, t, lval, non_constant_p,
+					   overflow_p);
+    }
+
+  return NULL_TREE;
+}
+
 /* Attempt to reduce the expression T to a constant value.
    On failure, issue diagnostic and return error_mark_node.  */
 /* FIXME unify with c_fully_fold */
@@ -3247,6 +3271,12 @@ cxx_eval_constant_expression (const constexpr_ctx *ctx, tree t,
       break;
 
     case POINTER_PLUS_EXPR:
+      r = cxx_eval_pointer_plus_expression (ctx, t, lval, non_constant_p,
+					    overflow_p);
+      if (r)
+	break;
+      /* else fall through */
+
     case PLUS_EXPR:
     case MINUS_EXPR:
     case MULT_EXPR:
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 792c267..d792b9f 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,5 +1,10 @@
 2015-03-30  Marek Polacek  <polacek@redhat.com>
 
+	PR c++/65398
+	* g++.dg/cpp0x/pr65398-2.C: New test.
+
+2015-03-30  Marek Polacek  <polacek@redhat.com>
+
 	* c-c++-common/pr65556.c: Change the width of bit-fields.
 
 2015-03-27  Jan Hubicka  <hubicka@ucw.cz>
diff --git a/gcc/testsuite/g++.dg/cpp0x/pr65398-2.C b/gcc/testsuite/g++.dg/cpp0x/pr65398-2.C
new file mode 100644
index 0000000..f920b03
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/pr65398-2.C
@@ -0,0 +1,38 @@
+// PR c++/65398
+// { dg-do compile { target c++11 } }
+
+#define SA(X) static_assert((X),#X)
+
+constexpr char s[] = "abc";
+
+SA((&s[0] + 0) == (&s[0] + 0));
+SA((&s[0] + 1) == (&s[1] + 0));
+SA((&s[0] + 2) == (&s[1] + 1));
+SA((&s[0] + 3) == (&s[1] + 2));
+SA((&s[0] + 4) == (&s[1] + 3));
+SA((&s[2] + 0) == (&s[0] + 2));
+SA((&s[2] + 1) == (&s[3] + 0));
+SA((&s[2] + 2) == (&s[3] + 1));
+SA((&s[4] + 0) == (&s[2] + 2));
+
+SA((&s[0] + 0) != (&s[1] + 0));
+SA((&s[0] + 2) != (&s[1] + 0));
+SA((&s[2] + 0) != (&s[2] + 1));
+SA((&s[1] + 1) != (&s[0] + 1));
+
+constexpr int l[] = { 'c', 'd', 'e', '\0' };
+
+SA((&l[0] + 0) == (&l[0] + 0));
+SA((&l[0] + 1) == (&l[1] + 0));
+SA((&l[0] + 2) == (&l[1] + 1));
+SA((&l[0] + 3) == (&l[1] + 2));
+SA((&l[0] + 4) == (&l[1] + 3));
+SA((&l[2] + 0) == (&l[0] + 2));
+SA((&l[2] + 1) == (&l[3] + 0));
+SA((&l[2] + 2) == (&l[3] + 1));
+SA((&l[4] + 0) == (&l[2] + 2));
+
+SA((&l[0] + 0) != (&l[1] + 0));
+SA((&l[0] + 2) != (&l[1] + 0));
+SA((&l[2] + 0) != (&l[2] + 1));
+SA((&l[1] + 1) != (&l[0] + 1));