df-problems.c (df_simulate_initialize_forwards): Set, don't clear, bits for…

df-problems.c (df_simulate_initialize_forwards): Set, don't clear, bits for artificial defs at the top of the block.

	* df-problems.c (df_simulate_initialize_forwards): Set, don't clear,
	bits for artificial defs at the top of the block.
	* fwprop.c (single_def_use_enter_block): Don't call it.

From-SVN: r158750

gcc/ChangeLog

+2010-04-26  Bernd Schmidt  <bernds@codesourcery.com>
+
+	* df-problems.c (df_simulate_initialize_forwards): Set, don't clear,
+	bits for artificial defs at the top of the block.
+	* fwprop.c (single_def_use_enter_block): Don't call it.
+
 2010-04-26  Jack Howarth <howarth@bromo.med.uc.edu>
 
 	PR 43715

gcc/df-problems.c

@@ -3913,13 +3913,9 @@ df_simulate_finalize_backwards (basic_block bb, bitmap live)
    the block, starting with the first one.
    ----------------------------------------------------------------------------*/
 
-/* Apply the artificial uses and defs at the top of BB in a forwards
-   direction.  ??? This is wrong; defs mark the point where a pseudo
-   becomes live when scanning forwards (unless a def is unused).  Since
-   there are no REG_UNUSED notes for artificial defs, passes that
-   require artificial defs probably should not call this function
-   unless (as is the case for fwprop) they are correct when liveness
-   bitmaps are *under*estimated.  */
+/* Initialize the LIVE bitmap, which should be copied from DF_LIVE_IN or
+   DF_LR_IN for basic block BB, for forward scanning by marking artificial
+   defs live.  */
 
 void
 df_simulate_initialize_forwards (basic_block bb, bitmap live)
@@ -3931,7 +3927,7 @@ df_simulate_initialize_forwards (basic_block bb, bitmap live)
     {
       df_ref def = *def_rec;
       if (DF_REF_FLAGS (def) & DF_REF_AT_TOP)
-	bitmap_clear_bit (live, DF_REF_REGNO (def));
+	bitmap_set_bit (live, DF_REF_REGNO (def));
     }
 }
 

gcc/fwprop.c

@@ -228,7 +228,10 @@ single_def_use_enter_block (struct dom_walk_data *walk_data ATTRIBUTE_UNUSED,
 
   process_uses (df_get_artificial_uses (bb_index), DF_REF_AT_TOP);
   process_defs (df_get_artificial_defs (bb_index), DF_REF_AT_TOP);
-  df_simulate_initialize_forwards (bb, local_lr);
+
+  /* We don't call df_simulate_initialize_forwards, as it may overestimate
+     the live registers if there are unused artificial defs.  We prefer
+     liveness to be underestimated.  */
 
   FOR_BB_INSNS (bb, insn)
     if (INSN_P (insn))