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[Bug tree-optimization/35805] [ira] error in start_allocno_priorities, at ira-color.c:1806
- From: "zadeck at naturalbridge dot com" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: 2 Jan 2009 00:38:54 -0000
- Subject: [Bug tree-optimization/35805] [ira] error in start_allocno_priorities, at ira-color.c:1806
- References: <bug-35805-14137@http.gcc.gnu.org/bugzilla/>
- Reply-to: gcc-bugzilla at gcc dot gnu dot org
------- Comment #4 from zadeck at naturalbridge dot com 2009-01-02 00:38 -------
Subject: Re: [ira] error in start_allocno_priorities,
at ira-color.c:1806
2009-01-01 Kenneth Zadeck <zadeck@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.
This patch fixes the problem. The comment in the patch describes the
issue. Since this was not really a failure, it would be hard to make
this issue into a testcase.
Ok to commit?
Bootstrapped and regression tested on x86*.
Kenny
Index: df-problems.c
===================================================================
--- df-problems.c (revision 142954)
+++ df-problems.c (working copy)
@@ -1001,22 +1001,32 @@ 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)
{
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