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

1 files changed, 16 insertions, 0 deletions

diff --git a/gcc/df-scan.c b/gcc/df-scan.c
index 7cfd34b..e6b55b5 100644
--- a/gcc/df-scan.c
+++ b/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);