[Bug debug/43762] New: VLA artificial length var loclist is missing DW_OP_stack_value

["jan dot kratochvil at redhat dot com" <gcc-bugzilla at gcc dot gnu dot org>]

gcc (GCC) 4.6.0 20100415 (experimental)
-O2 -g
-----------------------------------------------------------------------------
void __attribute__((noinline))
f (int l)
{
  char s[l];
}
int
main (void)
{
  f (5);
  return 0;
}
-----------------------------------------------------------------------------
 <2><63>: Abbrev Number: 5 (DW_TAG_variable)
    <64>   DW_AT_name        : s
    <68>   DW_AT_type        : <0x74>
 <1><74>: Abbrev Number: 7 (DW_TAG_array_type)
 <2><7d>: Abbrev Number: 8 (DW_TAG_subrange_type)
    <82>   DW_AT_upper_bound : <0x59>
 <2><59>: Abbrev Number: 4 (DW_TAG_variable)
    <5a>   DW_AT_artificial  : 1
    <5b>   DW_AT_type        : <0x8a>
    <5f>   DW_AT_location    : 0x83     (location list)
 <1><8a>: Abbrev Number: 10 (DW_TAG_const_type)
    <8b>   DW_AT_type        : <0x87>
 <1><87>: Abbrev Number: 9 (DW_TAG_base_type)
    <88>   DW_AT_byte_size   : 8
    <89>   DW_AT_encoding    : 7        (unsigned)

 <2><4c>: Abbrev Number: 3 (DW_TAG_formal_parameter)
    <4d>   DW_AT_name        : l
    <51>   DW_AT_type        : <0x6d>
    <55>   DW_AT_location    : 0x60     (location list)
 <1><6d>: Abbrev Number: 6 (DW_TAG_base_type)
    <6e>   DW_AT_byte_size   : 4
    <6f>   DW_AT_encoding    : 5        (signed)
    <70>   DW_AT_name        : int

Contents of the .debug_loc section:
    Offset   Begin    End      Expression
    00000060 0000000000400460 0000000000400468 (DW_OP_reg5)
    00000060 <End of list>
    00000083 0000000000400460 0000000000400463 (DW_OP_breg5: 0; DW_OP_const1u:
32; DW_OP_shl; DW_OP_const1u: 32; DW_OP_shra; DW_OP_const1s: -1; DW_OP_plus)
    00000083 0000000000400463 0000000000400468 (DW_OP_breg5: -1)
    00000083 0000000000400468 000000000040046c (DW_OP_breg5: -31)
    00000083 <End of list>
-----------------------------------------------------------------------------

I believe the loclist at 0x83 should have DW_OP_stack_value on each line.
Even according to recent (offlist) mail by Jakub these are "location
expressions".

I do not see in the DWARF spec. an explicit description what should mean a DIE
reference for DW_AT_upper_bound, currently generated by GCC as:
    <82>   DW_AT_upper_bound : <0x59>

I believe it was designed to supply there the real variable "l" holding the
value such as if it would be:
    <82>   DW_AT_upper_bound : <0x4c>

If an artificial variable calculating the same value is used the artificial
variable should simulate it has such _value_ (and not such its _address_).

(This problem is also affecting Fortran dynamic arrays with -O2 -g.)


-- 
           Summary: VLA artificial length var loclist is missing
                    DW_OP_stack_value
           Product: gcc
           Version: 4.6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: debug
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: jan dot kratochvil at redhat dot com
GCC target triplet: x86_64-unknown-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43762