2009-01-02 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.
	


git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@143027 138bc75d-0d04-0410-961f-82ee72b054a4

3 files changed, 29 insertions, 13 deletions

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index b52ed16a1ce..ba31727eaf1 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,10 @@
+2009-01-02  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.
+	
 2009-01-02  Mark Mitchell  <mark@codesourcery.com>
 
 	PR 33649
diff --git a/gcc/dce.c b/gcc/dce.c
index 1adea75570d..08a0f5048e3 100644
--- a/gcc/dce.c
+++ b/gcc/dce.c
@@ -601,7 +601,7 @@ dce_process_block (basic_block bb, bool redo_out, bitmap au)
 
   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));
     }
 
diff --git a/gcc/df-problems.c b/gcc/df-problems.c
index 9175f106c96..0bfef8a08eb 100644
--- a/gcc/df-problems.c
+++ b/gcc/df-problems.c
@@ -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;
 }