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

	PR c++/65398
	* constexpr.c (cxx_fold_indirect_ref): Transform *(&A[i] p+ j) into
	A[i + j].

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

From-SVN: r221544

gcc/cp/ChangeLog

 2015-03-20  Marek Polacek  <polacek@redhat.com>
 
+	PR c++/65398
+	* constexpr.c (cxx_fold_indirect_ref): Transform *(&A[i] p+ j) into
+	A[i + j].
+
+2015-03-20  Marek Polacek  <polacek@redhat.com>
+
 	PR c++/65072
 	* typeck.c (lookup_anon_field): Make sure we're dealing with the main
 	variant.

gcc/cp/constexpr.c

@@ -2427,6 +2427,27 @@ 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] */

gcc/testsuite/ChangeLog

+2015-03-20  Marek Polacek  <polacek@redhat.com>
+
+	PR c++/65398
+	* g++.dg/cpp0x/pr65398.C: New test.
+
 2015-03-20  Jan Hubicka  <hubicka@ucw.cz>
 
 	PR ipa/65475

gcc/testsuite/g++.dg/cpp0x/pr65398.C

+// PR c++/65398
+// { dg-do compile { target c++11 } }
+
+#define SA(X) static_assert((X),#X)
+
+constexpr char s[] = "abc";
+constexpr char c1 = *(&s[0] + 0);
+constexpr char c2 = *(&s[0] + 1);
+constexpr char c3 = *(&s[1] + 0);
+constexpr char c4 = *(&s[1] + 1);
+constexpr char c5 = *(&s[2] + 0);
+constexpr char c6 = *(&s[0] + 2);
+constexpr char c7 = *(&s[2] + 1);
+
+constexpr char d1 = *(&s[4] - 0); // { dg-error "array subscript out of bound" }
+constexpr char d2 = *(&s[4] - 1);
+constexpr char d3 = *(&s[4] - 2);
+constexpr char d4 = *(&s[4] - 3);
+constexpr char d5 = *(&s[4] - 4);
+constexpr char d6 = *(&s[4] - 5);  // { dg-error "negative array subscript" }
+
+/* Don't accept invalid stuff.  */
+constexpr char e1 = *(&s[5] - 1); // { dg-error "is not a constant expression" }
+constexpr char e2 = *(&s[5] - 2); // { dg-error "is not a constant expression" }
+constexpr char e3 = *(&s[5] - 3); // { dg-error "is not a constant expression" }
+
+SA (c1 == 'a');
+SA (c2 == 'b');
+SA (c3 == 'b');
+SA (c4 == 'c');
+SA (c5 == 'c');
+SA (c6 == 'c');
+SA (c7 == '\0');
+SA (d2 == '\0');
+SA (d3 == 'c');
+SA (d4 == 'b');
+SA (d5 == 'a');
+
+constexpr int l[] = { 'c', 'd', 'e', '\0' };
+constexpr int i1 = *(&l[0] + 0);
+constexpr int i2 = *(&l[0] + 1);
+constexpr int i3 = *(&l[1] + 0);
+constexpr int i4 = *(&l[1] + 1);
+constexpr int i5 = *(&l[2] + 0);
+constexpr int i6 = *(&l[0] + 2);
+constexpr int i7 = *(&l[2] + 1);
+
+constexpr char j1 = *(&l[4] - 0); // { dg-error "array subscript out of bound" }
+constexpr char j2 = *(&l[4] - 1);
+constexpr char j3 = *(&l[4] - 2);
+constexpr char j4 = *(&l[4] - 3);
+constexpr char j5 = *(&l[4] - 4);
+constexpr char j6 = *(&l[4] - 5);  // { dg-error "negative array subscript" }
+
+/* Don't accept invalid stuff.  */
+constexpr char k1 = *(&l[5] - 1); // { dg-error "is not a constant expression" }
+constexpr char k2 = *(&l[5] - 2); // { dg-error "is not a constant expression" }
+constexpr char k3 = *(&l[5] - 3); // { dg-error "is not a constant expression" }
+
+SA (i1 == 'c');
+SA (i2 == 'd');
+SA (i3 == 'd');
+SA (i4 == 'e');
+SA (i5 == 'e');
+SA (i6 == 'e');
+SA (i7 == '\0');
+SA (j2 == '\0');
+SA (j3 == 'e');
+SA (j4 == 'd');
+SA (j5 == 'c');