[gdb/symtab] Add optimized out static var to cooked index

Consider the test-case:
...
$ cat main.c
int main (void) { return 0; }
$ cat static-optimized-out.c
static int aaa;
...
compiled like this:
...
$ gcc-12 static-optimized-out.c main.c -g -O2 -flto
...

There's a difference in behaviour depending on symtab expansion state:
...
$ gdb -q -batch a.out -ex "print aaa"
No symbol "aaa" in current context.
$ gdb -q -batch a.out -ex "maint expand-symtab" -ex "print aaa"
$1 = <optimized out>
...

The reason for the difference is that the optimized out variable aaa:
...
 <1><104>: Abbrev Number: 2 (DW_TAG_variable)
    <105>   DW_AT_name        : aaa
    <109>   DW_AT_decl_file   : 1
    <10a>   DW_AT_decl_line   : 18
    <10b>   DW_AT_decl_column : 12
    <10c>   DW_AT_type        : <0x110>
...
is not added to the cooked index because of this clause in abbrev_table::read:
...
     else if (!has_location && !has_specification_or_origin && !has_external
	       && cur_abbrev->tag == DW_TAG_variable)
	cur_abbrev->interesting = false;
...

Fix this inconsistency by making sure that the optimized out variable is added
to the cooked index.

Regression tested on x86_64-linux.

Add two test-cases, a C test-case gdb.opt/static-optimized-out.exp and a dwarf
assembly test-case gdb.dwarf2/static-optimized-out.exp.

Tested gdb.opt/static-optimized-out.exp with gcc-8 to gcc-12, for which we now
consistently get:
...
(gdb) print aaa^M
$1 = <optimized out>^M
...
and with gcc 7.5.0 and clang 13.0.1, for which we still consistently get:
...
(gdb) print aaa^M
No symbol "aaa" in current context.^M
...
due to missing debug info for the variable.

PR symtab/30656
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=30656

Approved-By: Tom Tromey <tom@tromey.com>

gdb/dwarf2/abbrev.c

@@ -162,7 +162,6 @@ abbrev_table::read (struct dwarf2_section_info *section,
       bool has_specification_or_origin = false;
       bool has_name = false;
       bool has_linkage_name = false;
-      bool has_location = false;
       bool has_external = false;
 
       /* Now read in declarations.  */
@@ -217,11 +216,6 @@ abbrev_table::read (struct dwarf2_section_info *section,
 	      has_linkage_name = true;
 	      break;
 
-	    case DW_AT_const_value:
-	    case DW_AT_location:
-	      has_location = true;
-	      break;
-
 	    case DW_AT_sibling:
 	      if (is_csize && cur_attr.form == DW_FORM_ref4)
 		sibling_offset = size;
@@ -296,9 +290,6 @@ abbrev_table::read (struct dwarf2_section_info *section,
 	cur_abbrev->interesting = false;
       else if (!tag_interesting_for_index (cur_abbrev->tag))
 	cur_abbrev->interesting = false;
-      else if (!has_location && !has_specification_or_origin && !has_external
-	       && cur_abbrev->tag == DW_TAG_variable)
-	cur_abbrev->interesting = false;
       else
 	cur_abbrev->interesting = true;
 

gdb/testsuite/gdb.dwarf2/static-optimized-out.exp

@@ -0,0 +1,67 @@
+# Copyright 2023 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/>.
+
+# Check that an optimized out static variable is printed the same independent
+# of state of symtab expansion.  See also gdb.opt/static-optimized-out.exp.
+
+load_lib dwarf.exp
+
+# This test can only be run on targets which support DWARF-2 and use gas.
+require dwarf2_support
+
+standard_testfile main.c -dw.S
+
+# Make DWARF for the test.
+set asm_file [standard_output_file $srcfile2]
+Dwarf::assemble $asm_file {
+    cu {} {
+	compile_unit {
+	    {
+		language @DW_LANG_C
+	    }
+	} {
+	    declare_labels integer_label
+
+	    integer_label: DW_TAG_base_type {
+		{DW_AT_byte_size 4 DW_FORM_sdata}
+		{DW_AT_encoding  @DW_ATE_signed}
+		{DW_AT_name      integer}
+	    }
+
+	    DW_TAG_variable {
+		{name var}
+		{type :$integer_label}
+	    }
+	}
+    }
+}
+
+if { [prepare_for_testing "failed to prepare" ${testfile} \
+	  [list $srcfile $asm_file] {nodebug}] } {
+    return -1
+}
+
+gdb_test "print var" " = <optimized out>"
+
+# Expand all symbol tables.
+gdb_test_no_output "maint expand-symtabs"
+
+# Make sure we do an actual lookup rather than just returning the same as
+# before.
+gdb_test_no_output "maint flush symbol-cache"
+
+with_test_prefix "after expand-symtabs" {
+    gdb_test "print var" " = <optimized out>"
+}

gdb/testsuite/gdb.opt/main.c

@@ -0,0 +1,22 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2023 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/>.  */
+
+int
+main (void)
+{
+  return 0;
+}

gdb/testsuite/gdb.opt/static-optimized-out.c

@@ -0,0 +1,18 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2023 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/>.  */
+
+static int aaa;

gdb/testsuite/gdb.opt/static-optimized-out.exp

@@ -0,0 +1,49 @@
+# Copyright 2023 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/>.
+
+# Check that an optimized out static variable is printed the same independent
+# of state of symtab expansion.  See also gdb.dwarf2/static-optimized-out.exp.
+
+standard_testfile .c main.c
+
+set opts {}
+lappend opts debug
+lappend opts "optimize=-O2 -flto"
+
+if { [prepare_for_testing "failed to prepare" $testfile \
+	  [list $srcfile $srcfile2] $opts] } {
+    return -1
+}
+
+set val ""
+gdb_test_multiple "print aaa" "" {
+    -re -wrap "^(?:\\$$decimal = )?(.*)" {
+	set val $expect_out(1,string)
+    }
+}
+
+if { $val == "" } {
+    return
+}
+
+# Expand all symbol tables.
+gdb_test_no_output "maint expand-symtab"
+
+# Make sure we do an actual lookup rather than just returning the same as
+# before.
+gdb_test_no_output "maint flush symbol-cache"
+
+# Now check that we get the same result in both cases.
+gdb_test "print aaa" [string_to_regexp $val] "consistency"