Handle biased types

In Ada, the programmer can request that a range type with a non-zero
base be stored in the minimal number of bits required for the range.
This is done by biasing the values; so, for example, a range of -7..-4
may be stored as two bits with a bias of -7.

This patch implements this for gdb.  It is done by adding a bias to
struct range_bounds and then adjusting a few spots to handle this.

The test case is written to use -fgnat-encodings=minimal, but a future
compiler patch will change the compiler to emit DW_AT_GNU_bias with
-fgnat-encodings=gdb.  It seemed good to get the gdb patch in first.

Tested on x86-64 Fedora 29; plus a variety of targets using AdaCore's
internal test suite.

gdb/ChangeLog
2019-09-03  Tom Tromey  <tromey@adacore.com>

	* ada-valprint.c (ada_val_print_num): Don't recurse for range
	types.
	(has_negatives): Unbias a range type bound.
	* dwarf2read.c (read_subrange_type): Handle DW_AT_GNU_bias.
	* gdbtypes.c (operator==): Handle new field.
	(create_range_type): Add "bias" parameter.
	(create_static_range_type, resolve_dynamic_range): Update.
	* gdbtypes.h (struct range_bounds) <bias>: New member.
	(create_range_type): Add bias parameter.
	* printcmd.c (print_scalar_formatted): Unbias range types.
	* value.c (unpack_long): Unbias range types.
	(pack_long): Bias range types.

gdb/testsuite/ChangeLog
2019-09-03  Tom Tromey  <tromey@adacore.com>

	* gdb.ada/bias.exp: New file.
	* gdb.ada/bias/bias.adb: New file.
	* gdb.ada/print_chars.exp: Add regression test.
	* gdb.ada/print_chars/foo.adb (My_Character): New type.
	(MC): New variable.

6 files changed, 155 insertions, 1 deletions

diff --git a/gdb/testsuite/gdb.ada/bias.exp b/gdb/testsuite/gdb.ada/bias.exp
new file mode 100644
index 00000000000..76ca6c08c63
--- /dev/null
+++ b/gdb/testsuite/gdb.ada/bias.exp
@@ -0,0 +1,56 @@
+# Copyright 2019 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 bias
+
+if {[gdb_compile_ada "${srcfile}" "${binfile}" executable \
+	 {debug additional_flags=-fgnat-encodings=minimal}] != "" } {
+  return -1
+}
+
+clean_restart ${testfile}
+
+set bp_location [gdb_get_line_number "STOP" ${testdir}/bias.adb]
+runto "bias.adb:$bp_location"
+
+gdb_test "print x" " = 64"
+gdb_test "print y" " = -5"
+
+gdb_test "print cval" " = 65"
+gdb_test "print/c cval" " = 65 'A'"
+
+# Some binary arithmetic checks.
+gdb_test "print y < y1" " = false"
+gdb_test "print y <= y1" " = false"
+gdb_test "print y > y1" " = true"
+gdb_test "print y >= y1" " = true"
+gdb_test "print y = y" " = true"
+gdb_test "print y /= y" " = false"
+gdb_test "print y /= y1" " = true"
+
+gdb_test "print x + x1" " = 65"
+gdb_test "ptype x + x1" "type = range 1 \\.\\. 64"
+gdb_test "print x / x1" " = 64"
+gdb_test "print x * x1" " = 64"
+gdb_test "print x - x1" " = 63"
+
+# Test that storing un-biases.
+gdb_test "print x := 5" " = 5"
+gdb_test "print x" " = 5" "re-read x after storing"
+
+gdb_test "print spr" " = \\(r => -4, s => -5\\)"
+gdb_test "print a" " = \\(-7, -5, -4\\)"
diff --git a/gdb/testsuite/gdb.ada/bias/bias.adb b/gdb/testsuite/gdb.ada/bias/bias.adb
new file mode 100644
index 00000000000..ad46d20dd20
--- /dev/null
+++ b/gdb/testsuite/gdb.ada/bias/bias.adb
@@ -0,0 +1,52 @@
+--  Copyright 2019 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 Pck; use Pck;
+
+procedure Bias is
+   type Small is range -7 .. -4;
+   for Small'Size use 2;
+   Y : Small := -5;
+   Y1 : Small := -7;
+
+   type Repeat_Count_T is range 1 .. 2 ** 6;
+   for Repeat_Count_T'Size use 6;
+   X : Repeat_Count_T := 64;
+   X1 : Repeat_Count_T := 1;
+
+   type Char_Range is range 65 .. 68;
+   for Char_Range'Size use 2;
+   Cval : Char_Range := 65;
+
+   type Some_Packed_Record is record
+      R: Small;
+      S: Small;
+   end record;
+   pragma Pack (Some_Packed_Record);
+   SPR : Some_Packed_Record := (R => -4, S => -5);
+
+   type Packed_Array is array (1 .. 3) of Small;
+   pragma pack (Packed_Array);
+   A : Packed_Array := (-7, -5, -4);
+
+begin
+   Do_Nothing (Y'Address);		--  STOP
+   Do_Nothing (Y1'Address);
+   Do_Nothing (X'Address);
+   Do_Nothing (X1'Address);
+   Do_Nothing (Cval'Address);
+   Do_Nothing (SPR'Address);
+   Do_Nothing (A'Address);
+end Bias;
diff --git a/gdb/testsuite/gdb.ada/bias/pck.adb b/gdb/testsuite/gdb.ada/bias/pck.adb
new file mode 100644
index 00000000000..fb433861df0
--- /dev/null
+++ b/gdb/testsuite/gdb.ada/bias/pck.adb
@@ -0,0 +1,23 @@
+--  Copyright 2012-2019 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 body Pck is
+   procedure Do_Nothing (A : System.Address) is
+   begin
+      null;
+   end Do_Nothing;
+end Pck;
diff --git a/gdb/testsuite/gdb.ada/bias/pck.ads b/gdb/testsuite/gdb.ada/bias/pck.ads
new file mode 100644
index 00000000000..a40fa62c8eb
--- /dev/null
+++ b/gdb/testsuite/gdb.ada/bias/pck.ads
@@ -0,0 +1,20 @@
+--  Copyright 2012-2019 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;
diff --git a/gdb/testsuite/gdb.ada/print_chars.exp b/gdb/testsuite/gdb.ada/print_chars.exp
index 992b1347641..9a0e2157844 100644
--- a/gdb/testsuite/gdb.ada/print_chars.exp
+++ b/gdb/testsuite/gdb.ada/print_chars.exp
@@ -39,4 +39,4 @@ gdb_test "print WWC" \
          "= 99 'c'"  \
          "print WWC"
 
-
+gdb_test "print MC" " = 77 'M'"
diff --git a/gdb/testsuite/gdb.ada/print_chars/foo.adb b/gdb/testsuite/gdb.ada/print_chars/foo.adb
index 40d0c060942..c89c0d3cef9 100644
--- a/gdb/testsuite/gdb.ada/print_chars/foo.adb
+++ b/gdb/testsuite/gdb.ada/print_chars/foo.adb
@@ -19,6 +19,9 @@ procedure Foo is
    C : Character := 'a';
    WC : Wide_Character := 'b';
    WWC : Wide_Wide_Character := 'c';
+
+   type My_Character is new Character;
+   MC : My_Character := 'M';
 begin
    Do_Nothing (C'Address);  -- START
    Do_Nothing (WC'Address);