re PR c++/71504 ([C++11] constexpr fails with multidimensional arrays)

	PR c++/71504
	* constexpr.c (cxx_fold_indirect_ref_1): New function.
	(cxx_fold_indirect_ref): Use it.

	* g++.dg/cpp0x/constexpr-array21.C: New test.
	* g++.dg/cpp1y/constexpr-array7.C: New test.
	* g++.dg/cpp1z/constexpr-array1.C: New test.

2019-10-04  Jason Merrill  <jason@redhat.com>

	PR c++/71504
	* g++.dg/cpp0x/constexpr-array20.C: New test.

From-SVN: r276563

7 files changed, 223 insertions, 128 deletions

diff --git a/gcc/cp/ChangeLog b/gcc/cp/ChangeLog
index a11bdaf..e705bcc 100644
--- a/gcc/cp/ChangeLog
+++ b/gcc/cp/ChangeLog
@@ -1,5 +1,9 @@
 2019-10-04  Jakub Jelinek  <jakub@redhat.com>
 
+	PR c++/71504
+	* constexpr.c (cxx_fold_indirect_ref_1): New function.
+	(cxx_fold_indirect_ref): Use it.
+
 	PR c++/91974
 	* cp-gimplify.c (cp_gimplify_expr) <case CALL_EXPR>: For
 	-fstrong-eval-order ensure CALL_EXPR_FN side-effects are evaluated
diff --git a/gcc/cp/constexpr.c b/gcc/cp/constexpr.c
index 2008793..2dc57f1 100644
--- a/gcc/cp/constexpr.c
+++ b/gcc/cp/constexpr.c
@@ -3346,6 +3346,103 @@ same_type_ignoring_tlq_and_bounds_p (tree type1, tree type2)
   return same_type_ignoring_top_level_qualifiers_p (type1, type2);
 }
 
+/* Helper function for cxx_fold_indirect_ref_1, called recursively.  */
+
+static tree
+cxx_fold_indirect_ref_1 (location_t loc, tree type, tree op,
+			 unsigned HOST_WIDE_INT off, bool *empty_base)
+{
+  tree optype = TREE_TYPE (op);
+  unsigned HOST_WIDE_INT const_nunits;
+  if (off == 0)
+    {
+      if (similar_type_p (optype, type))
+	return op;
+      /* Also handle conversion to an empty base class, which
+	 is represented with a NOP_EXPR.  */
+      /* *(foo *)&complexfoo => __real__ complexfoo */
+      else if (TREE_CODE (optype) == COMPLEX_TYPE
+	       && similar_type_p (type, TREE_TYPE (optype)))
+	return build1_loc (loc, REALPART_EXPR, type, op);
+    }
+  /* ((foo*)&complexfoo)[1] => __imag__ complexfoo */
+  else if (TREE_CODE (optype) == COMPLEX_TYPE
+	   && similar_type_p (type, TREE_TYPE (optype))
+	   && tree_to_uhwi (TYPE_SIZE_UNIT (type)) == off)
+    return build1_loc (loc, IMAGPART_EXPR, type, op);
+  if (is_empty_class (type)
+      && CLASS_TYPE_P (optype)
+      && DERIVED_FROM_P (type, optype))
+    {
+      *empty_base = true;
+      return op;
+    }
+  /* ((foo*)&vectorfoo)[x] => BIT_FIELD_REF<vectorfoo,...> */
+  else if (VECTOR_TYPE_P (optype)
+	   && similar_type_p (type, TREE_TYPE (optype))
+	   && TYPE_VECTOR_SUBPARTS (optype).is_constant (&const_nunits))
+    {
+      unsigned HOST_WIDE_INT part_width = tree_to_uhwi (TYPE_SIZE_UNIT (type));
+      unsigned HOST_WIDE_INT max_offset = part_width * const_nunits;
+      if (off < max_offset && off % part_width == 0)
+	{
+	  tree index = bitsize_int (off * BITS_PER_UNIT);
+	  return build3_loc (loc, BIT_FIELD_REF, type, op,
+			     TYPE_SIZE (type), index);
+	}
+    }
+  /* ((foo *)&fooarray)[x] => fooarray[x] */
+  else if (TREE_CODE (optype) == ARRAY_TYPE
+	   && tree_fits_uhwi_p (TYPE_SIZE_UNIT (TREE_TYPE (optype)))
+	   && !integer_zerop (TYPE_SIZE_UNIT (TREE_TYPE (optype))))
+    {
+      tree type_domain = TYPE_DOMAIN (optype);
+      tree min_val = size_zero_node;
+      if (type_domain && TYPE_MIN_VALUE (type_domain))
+	min_val = TYPE_MIN_VALUE (type_domain);
+      unsigned HOST_WIDE_INT el_sz
+	= tree_to_uhwi (TYPE_SIZE_UNIT (TREE_TYPE (optype)));
+      unsigned HOST_WIDE_INT idx = off / el_sz;
+      unsigned HOST_WIDE_INT rem = off % el_sz;
+      if (tree_fits_uhwi_p (min_val))
+	{
+	  tree index = size_int (idx + tree_to_uhwi (min_val));
+	  op = build4_loc (loc, ARRAY_REF, TREE_TYPE (optype), op, index,
+			   NULL_TREE, NULL_TREE);
+	  return cxx_fold_indirect_ref_1 (loc, type, op, rem,
+					  empty_base);
+	}
+    }
+  /* ((foo *)&struct_with_foo_field)[x] => COMPONENT_REF */
+  else if (TREE_CODE (optype) == RECORD_TYPE)
+    {
+      for (tree field = TYPE_FIELDS (optype);
+	   field; field = DECL_CHAIN (field))
+	if (TREE_CODE (field) == FIELD_DECL
+	    && TREE_TYPE (field) != error_mark_node
+	    && tree_fits_uhwi_p (TYPE_SIZE_UNIT (TREE_TYPE (field))))
+	  {
+	    tree pos = byte_position (field);
+	    if (!tree_fits_uhwi_p (pos))
+	      continue;
+	    unsigned HOST_WIDE_INT upos = tree_to_uhwi (pos);
+	    unsigned el_sz
+	      = tree_to_uhwi (TYPE_SIZE_UNIT (TREE_TYPE (field)));
+	    if (upos <= off && off < upos + el_sz)
+	      {
+		tree cop = build3 (COMPONENT_REF, TREE_TYPE (field),
+				   op, field, NULL_TREE);
+		if (tree ret = cxx_fold_indirect_ref_1 (loc, type, cop,
+							off - upos,
+							empty_base))
+		  return ret;
+	      }
+	  }
+    }
+
+  return NULL_TREE;
+}
+
 /* A less strict version of fold_indirect_ref_1, which requires cv-quals to
    match.  We want to be less strict for simple *& folding; if we have a
    non-const temporary that we access through a const pointer, that should
@@ -3353,9 +3450,7 @@ same_type_ignoring_tlq_and_bounds_p (tree type1, tree type2)
    because we're dealing with things like ADDR_EXPR of INTEGER_CST which
    don't really make sense outside of constant expression evaluation.  Also
    we want to allow folding to COMPONENT_REF, which could cause trouble
-   with TBAA in fold_indirect_ref_1.
-
-   Try to keep this function synced with fold_indirect_ref_1.  */
+   with TBAA in fold_indirect_ref_1.  */
 
 static tree
 cxx_fold_indirect_ref (location_t loc, tree type, tree op0, bool *empty_base)
@@ -3386,139 +3481,19 @@ cxx_fold_indirect_ref (location_t loc, tree type, tree op0, bool *empty_base)
 	  else
 	    return op;
 	}
-      /* *(foo *)&fooarray => fooarray[0] */
-      else if (TREE_CODE (optype) == ARRAY_TYPE
-	       && similar_type_p (type, TREE_TYPE (optype)))
-	{
-	  tree type_domain = TYPE_DOMAIN (optype);
-	  tree min_val = size_zero_node;
-	  if (type_domain && TYPE_MIN_VALUE (type_domain))
-	    min_val = TYPE_MIN_VALUE (type_domain);
-	  return build4_loc (loc, ARRAY_REF, type, op, min_val,
-			     NULL_TREE, NULL_TREE);
-	}
-      /* *(foo *)&complexfoo => __real__ complexfoo */
-      else if (TREE_CODE (optype) == COMPLEX_TYPE
-	       && similar_type_p (type, TREE_TYPE (optype)))
-	return fold_build1_loc (loc, REALPART_EXPR, type, op);
-      /* *(foo *)&vectorfoo => BIT_FIELD_REF<vectorfoo,...> */
-      else if (VECTOR_TYPE_P (optype)
-	       && similar_type_p (type, TREE_TYPE (optype)))
-	{
-	  tree part_width = TYPE_SIZE (type);
-	  tree index = bitsize_int (0);
-	  return fold_build3_loc (loc, BIT_FIELD_REF, type, op, part_width,
-				  index);
-	}
-      /* Also handle conversion to an empty base class, which
-	 is represented with a NOP_EXPR.  */
-      else if (is_empty_class (type)
-	       && CLASS_TYPE_P (optype)
-	       && DERIVED_FROM_P (type, optype))
-	{
-	  *empty_base = true;
-	  return op;
-	}
-      /* *(foo *)&struct_with_foo_field => COMPONENT_REF */
-      else if (RECORD_OR_UNION_TYPE_P (optype))
-	{
-	  tree field = TYPE_FIELDS (optype);
-	  for (; field; field = DECL_CHAIN (field))
-	    if (TREE_CODE (field) == FIELD_DECL
-		&& TREE_TYPE (field) != error_mark_node
-		&& integer_zerop (byte_position (field))
-		&& similar_type_p (TREE_TYPE (field), type))
-	      return fold_build3 (COMPONENT_REF, type, op, field, NULL_TREE);
-	}
+      else
+	return cxx_fold_indirect_ref_1 (loc, type, op, 0, empty_base);
     }
   else if (TREE_CODE (sub) == POINTER_PLUS_EXPR
-	   && poly_int_tree_p (TREE_OPERAND (sub, 1), &const_op01))
+	   && tree_fits_uhwi_p (TREE_OPERAND (sub, 1)))
     {
       tree op00 = TREE_OPERAND (sub, 0);
       tree op01 = TREE_OPERAND (sub, 1);
 
       STRIP_NOPS (op00);
       if (TREE_CODE (op00) == ADDR_EXPR)
-	{
-	  tree op00type;
-	  op00 = TREE_OPERAND (op00, 0);
-	  op00type = TREE_TYPE (op00);
-
-	  /* ((foo*)&vectorfoo)[1] => BIT_FIELD_REF<vectorfoo,...> */
-	  if (VECTOR_TYPE_P (op00type)
-	      && similar_type_p (type, TREE_TYPE (op00type))
-	      /* POINTER_PLUS_EXPR second operand is sizetype, unsigned,
-		 but we want to treat offsets with MSB set as negative.
-		 For the code below negative offsets are invalid and
-		 TYPE_SIZE of the element is something unsigned, so
-		 check whether op01 fits into poly_int64, which implies
-		 it is from 0 to INTTYPE_MAXIMUM (HOST_WIDE_INT), and
-		 then just use poly_uint64 because we want to treat the
-		 value as unsigned.  */
-	      && tree_fits_poly_int64_p (op01))
-	    {
-	      tree part_width = TYPE_SIZE (type);
-	      poly_uint64 max_offset
-		= (tree_to_uhwi (part_width) / BITS_PER_UNIT
-		   * TYPE_VECTOR_SUBPARTS (op00type));
-	      if (known_lt (const_op01, max_offset))
-		{
-		  tree index = bitsize_int (const_op01 * BITS_PER_UNIT);
-		  return fold_build3_loc (loc,
-					  BIT_FIELD_REF, type, op00,
-					  part_width, index);
-		}
-	    }
-	  /* ((foo*)&complexfoo)[1] => __imag__ complexfoo */
-	  else if (TREE_CODE (op00type) == COMPLEX_TYPE
-		   && similar_type_p (type, TREE_TYPE (op00type)))
-	    {
-	      if (known_eq (wi::to_poly_offset (TYPE_SIZE_UNIT (type)),
-			    const_op01))
-		return fold_build1_loc (loc, IMAGPART_EXPR, type, op00);
-	    }
-	  /* ((foo *)&fooarray)[1] => fooarray[1] */
-	  else if (TREE_CODE (op00type) == ARRAY_TYPE
-		   && similar_type_p (type, TREE_TYPE (op00type)))
-	    {
-	      tree type_domain = TYPE_DOMAIN (op00type);
-	      tree min_val = size_zero_node;
-	      if (type_domain && TYPE_MIN_VALUE (type_domain))
-		min_val = TYPE_MIN_VALUE (type_domain);
-	      offset_int off = wi::to_offset (op01);
-	      offset_int el_sz = wi::to_offset (TYPE_SIZE_UNIT (type));
-	      offset_int remainder;
-	      off = wi::divmod_trunc (off, el_sz, SIGNED, &remainder);
-	      if (remainder == 0 && TREE_CODE (min_val) == INTEGER_CST)
-		{
-		  off = off + wi::to_offset (min_val);
-		  op01 = wide_int_to_tree (sizetype, off);
-		  return build4_loc (loc, ARRAY_REF, type, op00, op01,
-				     NULL_TREE, NULL_TREE);
-		}
-	    }
-	  /* Also handle conversion to an empty base class, which
-	     is represented with a NOP_EXPR.  */
-	  else if (is_empty_class (type)
-		   && CLASS_TYPE_P (op00type)
-		   && DERIVED_FROM_P (type, op00type))
-	    {
-	      *empty_base = true;
-	      return op00;
-	    }
-	  /* ((foo *)&struct_with_foo_field)[1] => COMPONENT_REF */
-	  else if (RECORD_OR_UNION_TYPE_P (op00type))
-	    {
-	      tree field = TYPE_FIELDS (op00type);
-	      for (; field; field = DECL_CHAIN (field))
-		if (TREE_CODE (field) == FIELD_DECL
-		    && TREE_TYPE (field) != error_mark_node
-		    && tree_int_cst_equal (byte_position (field), op01)
-		    && similar_type_p (TREE_TYPE (field), type))
-		  return fold_build3 (COMPONENT_REF, type, op00,
-				      field, NULL_TREE);
-	    }
-	}
+	return cxx_fold_indirect_ref_1 (loc, type, TREE_OPERAND (op00, 0),
+					tree_to_uhwi (op01), empty_base);
     }
   /* *(foo *)fooarrptr => (*fooarrptr)[0] */
   else if (TREE_CODE (TREE_TYPE (subtype)) == ARRAY_TYPE
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 1dce341..60e6caa 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,5 +1,17 @@
 2019-10-04  Jakub Jelinek  <jakub@redhat.com>
 
+	PR c++/71504
+	* g++.dg/cpp0x/constexpr-array21.C: New test.
+	* g++.dg/cpp1y/constexpr-array7.C: New test.
+	* g++.dg/cpp1z/constexpr-array1.C: New test.
+
+2019-10-04  Jason Merrill  <jason@redhat.com>
+
+	PR c++/71504
+	* g++.dg/cpp0x/constexpr-array20.C: New test.
+
+2019-10-04  Jakub Jelinek  <jakub@redhat.com>
+
 	PR c++/91974
 	* g++.dg/cpp1z/eval-order5.C: New test.
 
diff --git a/gcc/testsuite/g++.dg/cpp0x/constexpr-array20.C b/gcc/testsuite/g++.dg/cpp0x/constexpr-array20.C
new file mode 100644
index 0000000..217bbf4
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/constexpr-array20.C
@@ -0,0 +1,15 @@
+// PR c++/71504
+// { dg-do compile { target c++11 } }
+
+enum E { e };
+
+constexpr bool arr[1][1] = {{true}};
+
+template<E x, E y>
+void check() { 
+    static_assert(arr[x][y], ""); 
+}
+
+int main() { 
+    check<e, e>(); 
+}
diff --git a/gcc/testsuite/g++.dg/cpp0x/constexpr-array21.C b/gcc/testsuite/g++.dg/cpp0x/constexpr-array21.C
new file mode 100644
index 0000000..e085098
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/constexpr-array21.C
@@ -0,0 +1,27 @@
+// PR c++/71504
+// { dg-do compile { target c++11 } }
+
+typedef const char A4 [10];
+
+constexpr A4 a [] = { "123", "123456", "123456789" };
+
+constexpr int len (const char *s)
+{
+  return *s ? 1 + len (s + 1) : 0;
+}
+
+constexpr const char *s = a[0];
+constexpr const char *t = (a + 2)[-2];
+
+constexpr int n0 = len (s);
+constexpr int n1 = len (t);
+
+constexpr int n2 = len (a[0]);
+constexpr int n3 = len ((a + 2)[-2]);
+
+#define A(e) static_assert ((e), #e)
+
+A (n0 == 3);
+A (n0 == n1);
+A (n0 == n2);
+A (n0 == n3);
diff --git a/gcc/testsuite/g++.dg/cpp1y/constexpr-array7.C b/gcc/testsuite/g++.dg/cpp1y/constexpr-array7.C
new file mode 100644
index 0000000..30bd8fd
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1y/constexpr-array7.C
@@ -0,0 +1,16 @@
+// PR c++/71504
+// { dg-do compile { target c++14 } }
+
+template <typename A>
+constexpr auto
+sum (A const &a)
+{
+  int tot = 0;
+  for (auto &row : a)
+    for (auto elem : row)
+      tot += elem;
+  return tot;
+}
+
+constexpr int const a22[2][2] = {{1,2},{3,4}};
+static_assert (sum(a22) == 10, "badsum");
diff --git a/gcc/testsuite/g++.dg/cpp1z/constexpr-array1.C b/gcc/testsuite/g++.dg/cpp1z/constexpr-array1.C
new file mode 100644
index 0000000..02435d5
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1z/constexpr-array1.C
@@ -0,0 +1,46 @@
+// PR c++/71504
+// { dg-do compile { target c++17 } }
+
+typedef __SIZE_TYPE__ size_t;
+template <typename T, T v>
+struct integral_constant
+{
+  static constexpr T value = v;
+  typedef T value_type;
+  typedef integral_constant<T, v> type;
+  constexpr operator value_type () const noexcept { return value; }
+  constexpr value_type operator() () const noexcept { return value; }
+};
+template <typename T, T v>
+constexpr T integral_constant<T, v>::value;
+typedef integral_constant<bool, true> true_type;
+typedef integral_constant<bool, false> false_type;
+template <typename>
+struct is_array : public false_type { };
+template <typename T, size_t s>
+struct is_array<T[s]> : public true_type { };
+template <typename T>
+struct is_array<T[]> : public true_type { };
+template <bool, typename, typename>
+struct conditional;
+template <bool C, typename T, typename F>
+struct conditional { typedef T type; };
+template <typename T, typename F>
+struct conditional<false, T, F> { typedef F type; };
+template <typename T>
+struct array_ref;
+template <typename T>
+using ref_t = typename conditional<is_array<T>::value, array_ref<T>, T&>::type;
+template <typename T, unsigned N>
+struct array_ref<T[N]>
+{
+  T *a;
+  using const_reference = const ref_t<T>;
+  constexpr const_reference operator[] (unsigned I) const { return {a[I]}; }
+};
+template <typename A>
+array_ref (A&) -> array_ref<A>;
+constexpr int a2[2] = {1,2};
+static_assert (array_ref{a2}[0] == 1);
+constexpr int a22[2][2] = {{1,2},{3,4}};
+static_assert (array_ref{a22}[0][0] == 1);