------- Comment #16 from zadeck at naturalbridge dot com 2009-01-03 00:35
-------
Subject: Re: [ira] error in start_allocno_priorities,
at ira-color.c:1806
Kenneth Zadeck wrote:
> Steven Bosscher wrote:
>
>> On Fri, Jan 2, 2009 at 7:37 PM, Paolo Bonzini <bonz...@gnu.org> wrote:
>>
>>
>>>>> At this point, if your patch costs say 0.3%, and removing all traces
>>>>> DF_LR_RUN_DCE (instead scheduling a dozen more pass_fast_rtl_dce in
>>>>> passes.c) costs 0.5%, I'd rather see the latter, at least it's easier to
>>>>> look for opportunities to remove some useless DCE.
>>>>>
>>>>>
>>> I'll try to do this for 4.5.
>>>
>>>
>> It might be more worthwhile to just "fix" IRA to use DF_LIVE (which
>> Vlad should have done in the first place). Then we wouldn't need
>> Kenny's patch and DF_LR_RUN_DCE would still be essentially free.
>>
>> Gr.
>> Steven
>>
> There is the issue of correctness vs rot. I actually think that one of
> the reasons that flow was so bad was that people went down this long
> slippery slope of well it is good enough here ... and we really can get
> away with it not being right here ... and after a while, all you have is
> garbage.
>
> The problem with this game is that it is not maintainable. Those kinds
> of decisions tend to get forgotten and lost as the personnel supporting
> the compiler changes. Even if it is a fractional percentage slower,
> the fact that you do not have to reason about it as the compiler evolves
> is actually quite important.
>
> Thus, I plan to both fix this bug and add another one for vlad to fix
> the sets that he uses.
>
> Kenny
>
2009-01-02 Kenneth Zadeck <zad...@naturalbridge.com>
PR rtl-optimization/35805
* df-problems.c (df_lr_finalize): Add recursive call to resolve lr
problem if fast dce is able to remove any instructions.
* dce.c (dce_process_block): Fix dump message.
Rebootstrapped and regression tested on x86*.
Committed as revision 143027.
Kenny
Index: ChangeLog
===================================================================
--- ChangeLog (revision 142954)
+++ ChangeLog (working copy)
@@ -1,3 +1,10 @@
+2009-01-01 Kenneth Zadeck <zad...@naturalbridge.com>
+
+ PR rtl-optimization/35805
+ * df-problems.c (df_lr_finalize): Add recursive call to resolve lr
+ problem if fast dce is able to remove any instructions.
+ * dce.c (dce_process_block): Fix dump message.
+
2008-12-29 Seongbae Park <seongbae.p...@gmail.com>
* tree-profile.c (tree_init_ic_make_global_vars): Make static
Index: df-problems.c
===================================================================
--- df-problems.c (revision 142954)
+++ df-problems.c (working copy)
@@ -1001,25 +1001,34 @@ df_lr_transfer_function (int bb_index)
/* Run the fast dce as a side effect of building LR. */
static void
-df_lr_finalize (bitmap all_blocks ATTRIBUTE_UNUSED)
+df_lr_finalize (bitmap all_blocks)
{
+ df_lr->solutions_dirty = false;
if (df->changeable_flags & DF_LR_RUN_DCE)
{
run_fast_df_dce ();
- if (df_lr->problem_data && df_lr->solutions_dirty)
+
+ /* If dce deletes some instructions, we need to recompute the lr
+ solution before proceeding further. The problem is that fast
+ dce is a pessimestic dataflow algorithm. In the case where
+ it deletes a statement S inside of a loop, the uses inside of
+ S may not be deleted from the dataflow solution because they
+ were carried around the loop. While it is conservatively
+ correct to leave these extra bits, the standards of df
+ require that we maintain the best possible (least fixed
+ point) solution. The only way to do that is to redo the
+ iteration from the beginning. See PR35805 for an
+ example. */
+ if (df_lr->solutions_dirty)
{
- /* If we are here, then it is because we are both verifying
- the solution and the dce changed the function. In that case
- the verification info built will be wrong. So we leave the
- dirty flag true so that the verifier will skip the checking
- part and just clean up.*/
- df_lr->solutions_dirty = true;
+ df_clear_flags (DF_LR_RUN_DCE);
+ df_lr_alloc (all_blocks);
+ df_lr_local_compute (all_blocks);
+ df_worklist_dataflow (df_lr, all_blocks, df->postorder,
df->n_blocks);
+ df_lr_finalize (all_blocks);
+ df_set_flags (DF_LR_RUN_DCE);
}
- else
- df_lr->solutions_dirty = false;
}
- else
- df_lr->solutions_dirty = false;
}
Index: dce.c
===================================================================
--- dce.c (revision 142954)
+++ dce.c (working copy)
@@ -601,7 +601,7 @@ dce_process_block (basic_block bb, bool
if (dump_file)
{
- fprintf (dump_file, "processing block %d live out = ", bb->index);
+ fprintf (dump_file, "processing block %d lr out = ", bb->index);
df_print_regset (dump_file, DF_LR_OUT (bb));
}
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35805
