[Ada] Ignore __XA types when redundant.

Consider the following code which declares a variable A2 which
is an array of arrays of integers.

   type Array2_First is array (24 .. 26) of Integer;
   type Array2_Second is array (1 .. 2) of Array2_First;
   A1 : Array1_Second := ((10, 11, 12), (13, 14, 15));

Trying to print the type of that variable currently yields:

    (gdb) ptype A2
    type = array (1 .. 2, 24 .. 26) of integer

This is not correct, as this is the description of a two-dimension
array, which is different from an array of arrays. The expected
output is:

    (gdb) ptype a2
    type = array (1 .. 2) of foo_n926_029.array2_first

GDB's struct type currently handles multi-dimension arrays the same
way arrays of arrays, where each dimension is stored as a sub-array.
The ada-valprint module considers that consecutive array layers
are in fact multi-dimension arrays. For array of arrays, a typedef
layer is introduced between the two arrays, creating a break between
each array type.

In our situation, A2 is a described as a typedef of an array type...

        .uleb128 0x8    # (DIE (0x125) DW_TAG_variable)
        .ascii "a2\0"   # DW_AT_name
        .long   0xfc    # DW_AT_type

        .uleb128 0x4    # (DIE (0xfc) DW_TAG_typedef)
        .long   .LASF5  # DW_AT_name: "foo__array2_second"
        .long   0x107   # DW_AT_type

        .uleb128 0x5    # (DIE (0x107) DW_TAG_array_type)
        .long   .LASF5  # DW_AT_name: "foo__array2_second"
        .long   0xb4    # DW_AT_type
        .uleb128 0x6    # (DIE (0x114) DW_TAG_subrange_type)
        .long   0x11b   # DW_AT_type
        .byte   0x2     # DW_AT_upper_bound
        .byte   0       # end of children of DIE 0x107

... whose element type is, as expected, a typedef to the sub-array
type:

        .uleb128 0x4    # (DIE (0xb4) DW_TAG_typedef)
        .long   .LASF4  # DW_AT_name: "foo__array2_first"
        .long   0xbf    # DW_AT_type

        .uleb128 0x9    # (DIE (0xbf) DW_TAG_array_type)
        .long   .LASF4  # DW_AT_name: "foo__array2_first"
        .long   0xd8    # DW_AT_GNAT_descriptive_type
        .long   0x1c5   # DW_AT_type
        .uleb128 0xa    # (DIE (0xd0) DW_TAG_subrange_type)
        .long   0xf0    # DW_AT_type
        .byte   0x18    # DW_AT_lower_bound
        .byte   0x1a    # DW_AT_upper_bound
        .byte   0       # end of children of DIE 0xbf

The reason why things fails is that, during expression evaluation,
GDB tries to "fix" A1's type. Because the sub-array has a parallel
(descriptive) type (DIE 0xd8), GDB thinks that our array's index
type must be dynamic and therefore needs to be fixed. This in turn
causes the sub-array to be "fixed", which itself results in the
typedef layer to be stripped.

However, looking closer at the parallel type, we see...

        .uleb128 0xb    # (DIE (0xd8) DW_TAG_structure_type)
        .long   .LASF8  # DW_AT_name: "foo__array2_first___XA"
        [...]
        .uleb128 0xc    # (DIE (0xe4) DW_TAG_member)
        .long   .LASF10 # DW_AT_name: "foo__Tarray2_firstD1___XDLU_24__26"

... that all it tells us is that the array bounds are 24 and 26,
which is already correctly provided by the array's DW_TAG_subrange_type
bounds, meaning that this parallel type is just redundant.

Parallel types in general are slowly being removed in favor of
standard DWARF constructs. But in the meantime, this patch kills
two birds with one stone:

  1. It recognizes this situation where the XA type is useless,
     and saves an unnecessary range-type fixing;

  2. It fixes the issue at hand because ignoring the XA type results
     in no type fixing being required, which allows the typedef layer
     to be preserved.

gdb/ChangeLog:

        * ada-lang.c (ada_is_redundant_range_encoding): New function.
        (ada_is_redundant_index_type_desc): New function.
        (to_fixed_array_type): Ignore parallel XA type if redundant.

gdb/testsuite/ChangeLog:

        * gdb.ada/arr_arr: New testcase.

Tested on x86_64-linux.

7 files changed, 181 insertions, 0 deletions

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index fc336ad..c13c1d4 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,5 +1,11 @@
 2014-11-19  Joel Brobecker  <brobecker@adacore.com>
 
+	* ada-lang.c (ada_is_redundant_range_encoding): New function.
+	(ada_is_redundant_index_type_desc): New function.
+	(to_fixed_array_type): Ignore parallel XA type if redundant.
+
+2014-11-19  Joel Brobecker  <brobecker@adacore.com>
+
 	* ada-lang.c (constrained_packed_array_type): Set the length
 	of the return array as if both bounds where zero if that
 	returned array's index type is dynamic.
diff --git a/gdb/ada-lang.c b/gdb/ada-lang.c
index b3bb57c..077c29a 100644
--- a/gdb/ada-lang.c
+++ b/gdb/ada-lang.c
@@ -8311,6 +8311,68 @@ to_fixed_variant_branch_type (struct type *var_type0, const gdb_byte *valaddr,
     return TYPE_FIELD_TYPE (var_type, which);
 }
 
+/* Assuming RANGE_TYPE is a TYPE_CODE_RANGE, return nonzero if
+   ENCODING_TYPE, a type following the GNAT conventions for discrete
+   type encodings, only carries redundant information.  */
+
+static int
+ada_is_redundant_range_encoding (struct type *range_type,
+				 struct type *encoding_type)
+{
+  struct type *fixed_range_type;
+  char *bounds_str;
+  int n;
+  LONGEST lo, hi;
+
+  gdb_assert (TYPE_CODE (range_type) == TYPE_CODE_RANGE);
+
+  if (is_dynamic_type (range_type))
+    return 0;
+
+  if (TYPE_NAME (encoding_type) == NULL)
+    return 0;
+
+  bounds_str = strstr (TYPE_NAME (encoding_type), "___XDLU_");
+  if (bounds_str == NULL)
+    return 0;
+
+  n = 8; /* Skip "___XDLU_".  */
+  if (!ada_scan_number (bounds_str, n, &lo, &n))
+    return 0;
+  if (TYPE_LOW_BOUND (range_type) != lo)
+    return 0;
+
+  n += 2; /* Skip the "__" separator between the two bounds.  */
+  if (!ada_scan_number (bounds_str, n, &hi, &n))
+    return 0;
+  if (TYPE_HIGH_BOUND (range_type) != hi)
+    return 0;
+
+  return 1;
+}
+
+/* Given the array type ARRAY_TYPE, return nonzero if DESC_TYPE,
+   a type following the GNAT encoding for describing array type
+   indices, only carries redundant information.  */
+
+static int
+ada_is_redundant_index_type_desc (struct type *array_type,
+				  struct type *desc_type)
+{
+  struct type *this_layer = check_typedef (array_type);
+  int i;
+
+  for (i = 0; i < TYPE_NFIELDS (desc_type); i++)
+    {
+      if (!ada_is_redundant_range_encoding (TYPE_INDEX_TYPE (this_layer),
+					    TYPE_FIELD_TYPE (desc_type, i)))
+	return 0;
+      this_layer = check_typedef (TYPE_TARGET_TYPE (this_layer));
+    }
+
+  return 1;
+}
+
 /* Assuming that TYPE0 is an array type describing the type of a value
    at ADDR, and that DVAL describes a record containing any
    discriminants used in TYPE0, returns a type for the value that
@@ -8337,6 +8399,17 @@ to_fixed_array_type (struct type *type0, struct value *dval,
 
   index_type_desc = ada_find_parallel_type (type0, "___XA");
   ada_fixup_array_indexes_type (index_type_desc);
+  if (index_type_desc != NULL
+      && ada_is_redundant_index_type_desc (type0, index_type_desc))
+    {
+      /* Ignore this ___XA parallel type, as it does not bring any
+	 useful information.  This allows us to avoid creating fixed
+	 versions of the array's index types, which would be identical
+	 to the original ones.  This, in turn, can also help avoid
+	 the creation of fixed versions of the array itself.  */
+      index_type_desc = NULL;
+    }
+
   if (index_type_desc == NULL)
     {
       struct type *elt_type0 = ada_check_typedef (TYPE_TARGET_TYPE (type0));
diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog
index e86de0a..e18366d 100644
--- a/gdb/testsuite/ChangeLog
+++ b/gdb/testsuite/ChangeLog
@@ -1,5 +1,9 @@
 2014-11-19  Joel Brobecker  <brobecker@adacore.com>
 
+	* gdb.ada/arr_arr: New testcase.
+
+2014-11-19  Joel Brobecker  <brobecker@adacore.com>
+
 	* gdb.ada/pkd_arr_elem: New Testcase.
 
 2014-11-18  Luis Machado  <lgustavo@codesourcery.com>
diff --git a/gdb/testsuite/gdb.ada/arr_arr.exp b/gdb/testsuite/gdb.ada/arr_arr.exp
new file mode 100644
index 0000000..2be18e0
--- /dev/null
+++ b/gdb/testsuite/gdb.ada/arr_arr.exp
@@ -0,0 +1,33 @@
+# Copyright 2014 Free Software Foundation, Inc.
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+load_lib "ada.exp"
+
+standard_ada_testfile foo
+
+if {[gdb_compile_ada "${srcfile}" "${binfile}" executable [list debug ]] != "" } {
+  return -1
+}
+
+clean_restart ${testfile}
+
+set bp_location [gdb_get_line_number "START" ${testdir}/foo.adb]
+if ![runto "foo.adb:$bp_location" ] then {
+  perror "Couldn't run ${testfile}"
+  return
+}
+
+gdb_test "ptype a2" \
+         " = array \\(1 \\.\\. 2\\) of foo.array2_first"
diff --git a/gdb/testsuite/gdb.ada/arr_arr/foo.adb b/gdb/testsuite/gdb.ada/arr_arr/foo.adb
new file mode 100644
index 0000000..b4af104
--- /dev/null
+++ b/gdb/testsuite/gdb.ada/arr_arr/foo.adb
@@ -0,0 +1,25 @@
+--  Copyright 2014 Free Software Foundation, Inc.
+--
+--  This program is free software; you can redistribute it and/or modify
+--  it under the terms of the GNU General Public License as published by
+--  the Free Software Foundation; either version 3 of the License, or
+--  (at your option) any later version.
+--
+--  This program is distributed in the hope that it will be useful,
+--  but WITHOUT ANY WARRANTY; without even the implied warranty of
+--  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+--  GNU General Public License for more details.
+--
+--  You should have received a copy of the GNU General Public License
+--  along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+with System;
+with Pck; use Pck;
+
+procedure Foo is
+   type Array2_First is array (24 .. 26) of Integer;
+   type Array2_Second is array (1 .. 2) of Array2_First;
+   A2 : Array2_Second := ((10, 11, 12), (13, 14, 15));
+begin
+   Do_Nothing (A2'Address);  --  START
+end Foo;
diff --git a/gdb/testsuite/gdb.ada/arr_arr/pck.adb b/gdb/testsuite/gdb.ada/arr_arr/pck.adb
new file mode 100644
index 0000000..2b31332
--- /dev/null
+++ b/gdb/testsuite/gdb.ada/arr_arr/pck.adb
@@ -0,0 +1,21 @@
+--  Copyright 2014 Free Software Foundation, Inc.
+--
+--  This program is free software; you can redistribute it and/or modify
+--  it under the terms of the GNU General Public License as published by
+--  the Free Software Foundation; either version 3 of the License, or
+--  (at your option) any later version.
+--
+--  This program is distributed in the hope that it will be useful,
+--  but WITHOUT ANY WARRANTY; without even the implied warranty of
+--  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+--  GNU General Public License for more details.
+--
+--  You should have received a copy of the GNU General Public License
+--  along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package body Pck is
+   procedure Do_Nothing (A : System.Address) is
+   begin
+      null;
+   end Do_Nothing;
+end Pck;
diff --git a/gdb/testsuite/gdb.ada/arr_arr/pck.ads b/gdb/testsuite/gdb.ada/arr_arr/pck.ads
new file mode 100644
index 0000000..100d7d5
--- /dev/null
+++ b/gdb/testsuite/gdb.ada/arr_arr/pck.ads
@@ -0,0 +1,19 @@
+--  Copyright 2014 Free Software Foundation, Inc.
+--
+--  This program is free software; you can redistribute it and/or modify
+--  it under the terms of the GNU General Public License as published by
+--  the Free Software Foundation; either version 3 of the License, or
+--  (at your option) any later version.
+--
+--  This program is distributed in the hope that it will be useful,
+--  but WITHOUT ANY WARRANTY; without even the implied warranty of
+--  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+--  GNU General Public License for more details.
+--
+--  You should have received a copy of the GNU General Public License
+--  along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+with System;
+package Pck is
+   procedure Do_Nothing (A : System.Address);
+end Pck;