[PING][PATCH][exp] Interpret size of vla with unknown size as <optimized out>

[Tom de Vries <tdevries at suse dot de>]

Hi,

at -O3 -g -gstrict-dwarf, gcc generates for an optimized out vla 'a' a
DW_TAG_variable with type DW_TAG_array_type containing one
DW_TAG_subrange_type, but without DW_AT_upper_bound or DW_AT_count, which
makes the upper bound value 'unknown':
...
	.uleb128 0x15   # (DIE (0x161) DW_TAG_variable)
        .long   0xec    # DW_AT_abstract_origin
        .long   0x170   # DW_AT_type
	...
        .uleb128 0xa    # (DIE (0x170) DW_TAG_array_type)
        .long   0x110   # DW_AT_type
        .long   0x17f   # DW_AT_sibling
        .uleb128 0x17   # (DIE (0x179) DW_TAG_subrange_type)
        .long   0xc6    # DW_AT_type
        .byte   0       # end of children of DIE 0x170
...

But gdb prints '0' for the size of 'a':
...
/gdb ./vla-1.exe -batch -ex "b f1" -ex "run" -ex "p sizeof(a)"
Breakpoint 1 at 0x4004c0: f1. (2 locations)

Breakpoint 1, f1 (i=<optimized out>) at vla-1.c:18
18      }
$1 = 0
...
while <optimized out> would be more appropriate.

This patch fixes that in evaluate_subexp_for_sizeof.

Build and reg-tested on x86_64-linux.

OK for trunk?

Thanks,
- Tom

[gdb/exp] Interpret size of vla with unknown size as <optimized out>

2018-07-06  Tom de Vries  <tdevries@suse.de>

	* eval.c (evaluate_subexp_for_sizeof): Interpret size of dynamic type
	with undefined upper bound as <optimized out>.

	* gdb.base/vla-optimized-out-o3.c: New test.
	* gdb.base/vla-optimized-out-o3.exp: New file.

---
 gdb/eval.c                                      |  2 ++
 gdb/testsuite/gdb.base/vla-optimized-out-o3.c   | 34 +++++++++++++++++++++
 gdb/testsuite/gdb.base/vla-optimized-out-o3.exp | 40
+++++++++++++++++++++++++
 3 files changed, 76 insertions(+)

diff --git a/gdb/eval.c b/gdb/eval.c
index 9db6e7c69d..0495a11bfd 100644
--- a/gdb/eval.c
+++ b/gdb/eval.c
@@ -3145,6 +3145,8 @@ evaluate_subexp_for_sizeof (struct expression
*exp, int *pos,
 	{
 	  val = evaluate_subexp (NULL_TYPE, exp, pos, EVAL_NORMAL);
 	  type = value_type (val);
+	  if (TYPE_HIGH_BOUND_UNDEFINED (TYPE_INDEX_TYPE (type)))
+	    return allocate_optimized_out_value (size_type);
 	}
       else
 	(*pos) += 4;
diff --git a/gdb/testsuite/gdb.base/vla-optimized-out-o3.c
b/gdb/testsuite/gdb.base/vla-optimized-out-o3.c
new file mode 100644
index 0000000000..799a1f7b10
--- /dev/null
+++ b/gdb/testsuite/gdb.base/vla-optimized-out-o3.c
@@ -0,0 +1,34 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2018 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 __attribute__((noinline))
+f1 (int i)
+{
+  char a[i + 1];
+  a[0] = 5;
+  return a[0];
+}
+
+int
+main (void)
+{
+  volatile int j;
+  int i = 5;
+  asm volatile ("" : "=r" (i) : "0" (i));
+  j = f1 (i);
+  return 0;
+}
diff --git a/gdb/testsuite/gdb.base/vla-optimized-out-o3.exp
b/gdb/testsuite/gdb.base/vla-optimized-out-o3.exp
new file mode 100644
index 0000000000..bc435cc4aa
--- /dev/null
+++ b/gdb/testsuite/gdb.base/vla-optimized-out-o3.exp
@@ -0,0 +1,40 @@
+# Copyright 2018 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 whether we can determine the size of an optimized-out vla.
+
+standard_testfile
+
+if { [prepare_for_testing "failed to prepare" $testfile $srcfile \
+	  {debug optimize=-O3 additional_flags=-gstrict-dwarf}] } {
+    return -1
+}
+
+proc vla_optimized_out { } {
+    if ![runto f1] {
+	fail "can't run to f1"
+	return
+    }
+
+    gdb_test "p a" \
+	{ = <optimized out>} \
+	"printed optimized out vla"
+
+    gdb_test "p sizeof (a)" \
+	{ = <optimized out>} \
+	"printed optimized out size of optimized out vla"
+}
+
+vla_optimized_out