> Am 13.12.2022 um 17:54 schrieb Claudiu Zissulescu Ianculescu via Gcc
> <gcc@gcc.gnu.org>:
>
> UPDATE:
> The df_analyze_loop is calling the df_set_blocks. Thus, the analysis
> behaves as if the function only contains those blocks and any edges
> that occur directly between the blocks in the set (see df-core.cc).
> This said, the loop-doloop behaves faulty at loop-doloop.cc:772 as the
> df_get_lives_out (loop_end) is not computed correctly.
>
> A possible solution is to include in the blocks_to_analyze the missing
> basic blocks, something like:
>
> diff --git a/gcc/df-core.cc b/gcc/df-core.cc
> index a901b84878f..d7059c188b2 100644
> --- a/gcc/df-core.cc
> +++ b/gcc/df-core.cc
> @@ -1437,7 +1437,15 @@ df_analyze_loop (class loop *loop)
> df_set_blocks (blocks);
> BITMAP_FREE (blocks);
>
> - df_analyze_1 ();
> + /* Add the loop's header successor bbs too. */
> + edge e;
> + edge_iterator ei;
> + FOR_EACH_EDGE (e, ei, loop->header->succs)
> + bitmap_set_bit (df->blocks_to_analyze, e->dest->index);
> +
> + if (dump_file)
> + debug_bitmap_file (dump_file, df->blocks_to_analyze);
> + df_analyze ();
> }
>
> What do you think,
Maybe you want to iterate over the loops exit edges and include their
destination block instead?
> Claudiu
>
>> On Tue, Dec 13, 2022 at 2:30 PM Claudiu Zissulescu Ianculescu
>> <claz...@gmail.com> wrote:
>>
>> It looks like that. The df_analyze_loop is only looking at the loop
>> BBs, and it is not clear for me if df_analyze_loop is required to have
>> all the df_live_outs correctly computed or not. Do you know if it is
>> true?
>>
>> If the df_analyze_loop is not supposed to compute all the df_live_outs
>> correctly, then the error resides in how loop-doloop is using the
>> iv_analysis_loop_init().
>>
>> Thank you for your help,
>> Claudiu
>>
>>> On Tue, Dec 13, 2022 at 10:41 AM Eric Botcazou <botca...@adacore.com> wrote:
>>>
>>>> The problem shows in loop-doloop.c when I introduce a loop end pattern
>>>> that replaces the first jump instruction (JUMP_INSN 15) with a pattern
>>>> that clobbers CC reg. However, the DF doesn't look like it works as
>>>> the doloop step cannot find the CC reg alive. Please see
>>>> loop-doloop.c:766. Hence, it introduces the doloop_end patterns, and
>>>> renders the compare instruction (INSN 14) dead code. leading to
>>>> errors.
>>>
>>> So df_get_live_out does not contain the CC register? iv_analysis_loop_init
>>> only performs a local update of the DF information, maybe it does not cover
>>> the basic block containing insn 14 and 15?
>>>
>>> --
>>> Eric Botcazou
>>>
>>>
