On 8/20/24 13:00, Richard Biener wrote:
> On Fri, Aug 16, 2024 at 12:49 PM Bernd Edlinger
> <bernd.edlin...@hotmail.de> wrote:
>>
>> While this already works correctly for the case when an inlined
>> subroutine contains only one subrange, a redundant DW_TAG_lexical_block
>> is still emitted when the subroutine has multiple blocks.
>
> Huh. The point is that the inline context is a single scope block with no
> siblings - how did that get messed up? The patch unfortunately does not
> contain a testcase.
>
Well, I became aware of this because I am working on a gdb patch,
which improves the debug experience of optimized C code, and to my surprise
the test case did not work with gcc-8, while gcc-9 and following were fine.
Initially I did not see what is wrong, therefore I started to bisect when
this changed, and so I found your patch, which removed some lexical blocks
in the debug info of this gdb test case:
from binutils-gdb/gdb/testsuite/gdb.cp/step-and-next-inline.cc
in case you have the binutils-gdb already downloaded you can skip this:
$ git clone git://sourceware.org/git/binutils-gdb
$ cd binutils-gdb/gdb/testsuite/gdb.cp
$ gcc -g -O2 step-and-next-inline.cc
when you look at the debug info with readelf -w a.out
you will see, that the function "tree_check"
is inlined three times, one looks like this
<2><86b>: Abbrev Number: 40 (DW_TAG_inlined_subroutine)
<86c> DW_AT_abstract_origin: <0x95b>
<870> DW_AT_entry_pc : 0x1175
<878> DW_AT_GNU_entry_view: 0
<879> DW_AT_ranges : 0x21
<87d> DW_AT_call_file : 1
<87e> DW_AT_call_line : 52
<87f> DW_AT_call_column : 10
<880> DW_AT_sibling : <0x8bf>
<3><884>: Abbrev Number: 8 (DW_TAG_formal_parameter)
<885> DW_AT_abstract_origin: <0x974>
<889> DW_AT_location : 0x37 (location list)
<88d> DW_AT_GNU_locviews: 0x35
<3><891>: Abbrev Number: 8 (DW_TAG_formal_parameter)
<892> DW_AT_abstract_origin: <0x96c>
<896> DW_AT_location : 0x47 (location list)
<89a> DW_AT_GNU_locviews: 0x45
<3><89e>: Abbrev Number: 41 (DW_TAG_lexical_block)
<89f> DW_AT_ranges : 0x21
see the lexical block has the same DW_AT_ranges, as the
inlined subroutine, but the other invocations do not
have this lexical block, since your original fix removed
those.
And this lexical block triggered an unexpected issue
in my gdb patch, which I owe you one, for helping me
finding it :-)
Before that I have never looked at these lexical blocks,
but all I can say is that while compiling this test case,
in the first invocation of gen_inlined_subroutine_die
there are several SUBBLOCKS linked via BLOCK_CHAIN,
and only the first one is used to emit the lexical_block,
while the other siblings must be fully decoded, otherwise
there is an internal error, that I found by try-and-error.
I thought that is since the subroutine is split over several
places, and therefore it appeared natural to me, that the
subroutine is also using several SUBBLOCKS.
Thanks
Bernd.
> Richard.
>
>> Fixes: ac02e5b75451 ("re PR debug/37801 (DWARF output for inlined functions
>> doesn't always use DW_TAG_inlined_subroutine)")
>>
>> gcc/ChangeLog:
>>
>> PR debug/87440
>> * dwarf2out.cc (gen_inlined_subroutine_die): Handle the case
>> of multiple subranges correctly.
>> ---
>> some more context is here:
>> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87440#c5
>> Bootstrapped and regression-tested on x86_64-pc-linux-gnu, OK for trunk?
>>
>> gcc/dwarf2out.cc | 11 ++++++++---
>> 1 file changed, 8 insertions(+), 3 deletions(-)
>>
>> diff --git a/gcc/dwarf2out.cc b/gcc/dwarf2out.cc
>> index 357efaa5990..346feeb53c8 100644
>> --- a/gcc/dwarf2out.cc
>> +++ b/gcc/dwarf2out.cc
>> @@ -25171,9 +25171,10 @@ gen_inlined_subroutine_die (tree stmt, dw_die_ref
>> context_die)
>> Do that by doing the recursion to subblocks on the single subblock
>> of STMT. */
>> bool unwrap_one = false;
>> - if (BLOCK_SUBBLOCKS (stmt) && !BLOCK_CHAIN (BLOCK_SUBBLOCKS (stmt)))
>> + tree sub = BLOCK_SUBBLOCKS (stmt);
>> + if (sub)
>> {
>> - tree origin = block_ultimate_origin (BLOCK_SUBBLOCKS (stmt));
>> + tree origin = block_ultimate_origin (sub);
>> if (origin
>> && TREE_CODE (origin) == BLOCK
>> && BLOCK_SUPERCONTEXT (origin) == decl)
>> @@ -25181,7 +25182,11 @@ gen_inlined_subroutine_die (tree stmt, dw_die_ref
>> context_die)
>> }
>> decls_for_scope (stmt, subr_die, !unwrap_one);
>> if (unwrap_one)
>> - decls_for_scope (BLOCK_SUBBLOCKS (stmt), subr_die);
>> + {
>> + decls_for_scope (sub, subr_die);
>> + for (sub = BLOCK_CHAIN (sub); sub; sub = BLOCK_CHAIN (sub))
>> + gen_block_die (sub, subr_die);
>> + }
>> }
>>
>> /* Generate a DIE for a field in a record, or structure. CTX is required:
>> see
>> --
>> 2.39.2
>>
