df: Change defs in entry and uses in exit block during separate shrink-wrapping

So far all target implementations of the separate shrink-wrapping hooks
use the DF LIVE info to figure out around which basic blocks the non-
volatile registers need to be saved.  This is done by looking at the
IN+GEN+KILL sets of the basic blocks.  However, that doesn't work for
registers that DF says are defined in the entry block, or used in the
exit block.

This patch introduces a local flag DF_SCAN_EMPTY_ENTRY_EXIT that says
no registers should be defined in the entry block, and none used in the
exit block.  It also makes try_shrink_wrapping_separate use it.  The
rs6000 port is changed to use IN+GEN+KILL for the LR component.


	* config/rs6000/rs6000.c (rs6000_components_for_bb): Mark the LR
	component as used also if LR_REGNO is a live input to the bb.
	* df-scan.c (df_get_entry_block_def_set): Return immediately after
	clearing the set if DF_SCAN_EMPTY_ENTRY_EXIT is set.
	(df_get_exit_block_use_set): Ditto.
	* df.h (df_scan_flags): New enum.
	* shrink-wrap.c (try_shrink_wrapping_separate): Set
	DF_SCAN_EMPTY_ENTRY_EXIT in df_scan->local_flags, and call
	df_update_entry_block_defs and df_update_exit_block_uses
	at the start; clear the flag and call those functions at the end.

From-SVN: r242497

gcc/ChangeLog

@@ -1,3 +1,16 @@
+2016-11-16  Segher Boessenkool  <segher@kernel.crashing.org>
+
+	* config/rs6000/rs6000.c (rs6000_components_for_bb): Mark the LR
+	component as used also if LR_REGNO is a live input to the bb.
+	* df-scan.c (df_get_entry_block_def_set): Return immediately after
+	clearing the set if DF_SCAN_EMPTY_ENTRY_EXIT is set.
+	(df_get_exit_block_use_set): Ditto.
+	* df.h (df_scan_flags): New enum.
+	* shrink-wrap.c (try_shrink_wrapping_separate): Set
+	DF_SCAN_EMPTY_ENTRY_EXIT in df_scan->local_flags, and call
+	df_update_entry_block_defs and df_update_exit_block_uses
+	at the start; clear the flag and call those functions at the end.
+
 2016-11-16  Richard Sandiford  <richard.sandiford@arm.com>
 	    Alan Hayward  <alan.hayward@arm.com>
 	    David Sherwood  <david.sherwood@arm.com>

gcc/config/rs6000/rs6000.c

@@ -27823,7 +27823,8 @@ rs6000_components_for_bb (basic_block bb)
       bitmap_set_bit (components, regno);
 
   /* LR needs to be saved around a bb if it is killed in that bb.  */
-  if (bitmap_bit_p (gen, LR_REGNO)
+  if (bitmap_bit_p (in, LR_REGNO)
+      || bitmap_bit_p (gen, LR_REGNO)
       || bitmap_bit_p (kill, LR_REGNO))
     bitmap_set_bit (components, 0);
 

gcc/df-scan.c

@@ -3506,6 +3506,14 @@ df_get_entry_block_def_set (bitmap entry_block_defs)
 
   bitmap_clear (entry_block_defs);
 
+  /* For separate shrink-wrapping we use LIVE to analyze which basic blocks
+     need a prologue for some component to be executed before that block,
+     and we do not care about any other registers.  Hence, we do not want
+     any register for any component defined in the entry block, and we can
+     just leave all registers undefined.  */
+  if (df_scan->local_flags & DF_SCAN_EMPTY_ENTRY_EXIT)
+    return;
+
   for (i = 0; i < FIRST_PSEUDO_REGISTER; i++)
     {
       if (global_regs[i])
@@ -3665,6 +3673,14 @@ df_get_exit_block_use_set (bitmap exit_block_uses)
 
   bitmap_clear (exit_block_uses);
 
+  /* For separate shrink-wrapping we use LIVE to analyze which basic blocks
+     need an epilogue for some component to be executed after that block,
+     and we do not care about any other registers.  Hence, we do not want
+     any register for any component seen as used in the exit block, and we
+     can just say no registers at all are used.  */
+  if (df_scan->local_flags & DF_SCAN_EMPTY_ENTRY_EXIT)
+    return;
+
   /* Stack pointer is always live at the exit.  */
   bitmap_set_bit (exit_block_uses, STACK_POINTER_REGNUM);
 

gcc/df.h

@@ -450,6 +450,13 @@ enum df_chain_flags
   DF_UD_CHAIN      =  2  /* Build UD chains.  */
 };
 
+enum df_scan_flags
+{
+  /* Flags for the SCAN problem.  */
+  DF_SCAN_EMPTY_ENTRY_EXIT = 1  /* Don't define any registers in the entry
+				   block; don't use any in the exit block.  */
+};
+
 enum df_changeable_flags
 {
   /* Scanning flags.  */

gcc/shrink-wrap.c

@@ -1682,7 +1682,13 @@ try_shrink_wrapping_separate (basic_block first_bb)
   if (!components)
     return;
 
-  /* We need LIVE info.  */
+  /* We need LIVE info, not defining anything in the entry block and not
+     using anything in the exit block.  A block then needs a component if
+     the register for that component is in the IN or GEN or KILL set for
+     that block.  */
+  df_scan->local_flags |= DF_SCAN_EMPTY_ENTRY_EXIT;
+  df_update_entry_block_defs ();
+  df_update_exit_block_uses ();
   df_live_add_problem ();
   df_live_set_all_dirty ();
   df_analyze ();
@@ -1748,9 +1754,10 @@ try_shrink_wrapping_separate (basic_block first_bb)
   free_dominance_info (CDI_DOMINATORS);
   free_dominance_info (CDI_POST_DOMINATORS);
 
-  if (crtl->shrink_wrapped_separate)
-    {
-      df_live_set_all_dirty ();
-      df_analyze ();
-    }
+  /* All done.  */
+  df_scan->local_flags &= ~DF_SCAN_EMPTY_ENTRY_EXIT;
+  df_update_entry_block_defs ();
+  df_update_exit_block_uses ();
+  df_live_set_all_dirty ();
+  df_analyze ();
 }