* cse.c (is_dead_reg): Change into inline function that is not

	called through for_each_rtx.
	(set_live_p): Adjust caller.
	(insn_live_p): Don't reset DEBUG_INSNs here.
	(struct dead_debug_insn_data): New data. 
	(count_stores, is_dead_debug_insn, replace_dead_reg): New functions.
	(delete_trivially_dead_insns): If there is just one setter for the
	dead reg that is referenced by some DEBUG_INSNs, create a DEBUG_EXPR
	and add DEBUG_INSN for it right before the removed setter and
	use the DEBUG_EXPR instead of the dead pseudo.


git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@165452 138bc75d-0d04-0410-961f-82ee72b054a4

1 files changed, 166 insertions, 25 deletions

diff --git a/gcc/cse.c b/gcc/cse.c
index 4d10c842e0f..3ab6b37a8ea 100644
--- a/gcc/cse.c
+++ b/gcc/cse.c
@@ -1,6 +1,6 @@
 /* Common subexpression elimination for GNU compiler.
    Copyright (C) 1987, 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998
-   1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009
+   1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010
    Free Software Foundation, Inc.
 
 This file is part of GCC.
@@ -6698,14 +6698,11 @@ count_reg_usage (rtx x, int *counts, rtx dest, int incr)
     }
 }
 
-/* Return true if a register is dead.  Can be used in for_each_rtx.  */
+/* Return true if X is a dead register.  */
 
-static int
-is_dead_reg (rtx *loc, void *data)
+static inline int
+is_dead_reg (rtx x, int *counts)
 {
-  rtx x = *loc;
-  int *counts = (int *)data;
-
   return (REG_P (x)
 	  && REGNO (x) >= FIRST_PSEUDO_REGISTER
 	  && counts[REGNO (x)] == 0);
@@ -6731,7 +6728,7 @@ set_live_p (rtx set, rtx insn ATTRIBUTE_UNUSED, /* Only used with HAVE_cc0.  */
 	       || !reg_referenced_p (cc0_rtx, PATTERN (tem))))
     return false;
 #endif
-  else if (!is_dead_reg (&SET_DEST (set), counts)
+  else if (!is_dead_reg (SET_DEST (set), counts)
 	   || side_effects_p (SET_SRC (set)))
     return true;
   return false;
@@ -6775,21 +6772,68 @@ insn_live_p (rtx insn, int *counts)
 	else if (INSN_VAR_LOCATION_DECL (insn) == INSN_VAR_LOCATION_DECL (next))
 	  return false;
 
-      /* If this debug insn references a dead register, drop the
-	 location expression for now.  ??? We could try to find the
-	 def and see if propagation is possible.  */
-      if (for_each_rtx (&INSN_VAR_LOCATION_LOC (insn), is_dead_reg, counts))
-	{
-	  INSN_VAR_LOCATION_LOC (insn) = gen_rtx_UNKNOWN_VAR_LOC ();
-	  df_insn_rescan (insn);
-	}
-
       return true;
     }
   else
     return true;
 }
 
+/* Count the number of stores into pseudo.  Callback for note_stores.  */
+
+static void
+count_stores (rtx x, const_rtx set ATTRIBUTE_UNUSED, void *data)
+{
+  int *counts = (int *) data;
+  if (REG_P (x) && REGNO (x) >= FIRST_PSEUDO_REGISTER)
+    counts[REGNO (x)]++;
+}
+
+struct dead_debug_insn_data
+{
+  int *counts;
+  rtx *replacements;
+  bool seen_repl;
+};
+
+/* Return if a DEBUG_INSN needs to be reset because some dead
+   pseudo doesn't have a replacement.  Callback for for_each_rtx.  */
+
+static int
+is_dead_debug_insn (rtx *loc, void *data)
+{
+  rtx x = *loc;
+  struct dead_debug_insn_data *ddid = (struct dead_debug_insn_data *) data;
+
+  if (is_dead_reg (x, ddid->counts))
+    {
+      if (ddid->replacements && ddid->replacements[REGNO (x)] != NULL_RTX)
+	ddid->seen_repl = true;
+      else
+	return 1;
+    }
+  return 0;
+}
+
+/* Replace a dead pseudo in a DEBUG_INSN with replacement DEBUG_EXPR.
+   Callback for simplify_replace_fn_rtx.  */
+
+static rtx
+replace_dead_reg (rtx x, const_rtx old_rtx ATTRIBUTE_UNUSED, void *data)
+{
+  rtx *replacements = (rtx *) data;
+
+  if (REG_P (x)
+      && REGNO (x) >= FIRST_PSEUDO_REGISTER
+      && replacements[REGNO (x)] != NULL_RTX)
+    {
+      if (GET_MODE (x) == GET_MODE (replacements[REGNO (x)]))
+	return replacements[REGNO (x)];
+      return lowpart_subreg (GET_MODE (x), replacements[REGNO (x)],
+			     GET_MODE (replacements[REGNO (x)]));
+    }
+  return NULL_RTX;
+}
+
 /* Scan all the insns and delete any that are dead; i.e., they store a register
    that is never used or they copy a register to itself.
 
@@ -6803,22 +6847,51 @@ delete_trivially_dead_insns (rtx insns, int nreg)
 {
   int *counts;
   rtx insn, prev;
+  rtx *replacements = NULL;
   int ndead = 0;
 
   timevar_push (TV_DELETE_TRIVIALLY_DEAD);
   /* First count the number of times each register is used.  */
-  counts = XCNEWVEC (int, nreg);
-  for (insn = insns; insn; insn = NEXT_INSN (insn))
-    if (INSN_P (insn))
-      count_reg_usage (insn, counts, NULL_RTX, 1);
-
+  if (MAY_HAVE_DEBUG_INSNS)
+    {
+      counts = XCNEWVEC (int, nreg * 3);
+      for (insn = insns; insn; insn = NEXT_INSN (insn))
+	if (DEBUG_INSN_P (insn))
+	  count_reg_usage (INSN_VAR_LOCATION_LOC (insn), counts + nreg,
+			   NULL_RTX, 1);
+	else if (INSN_P (insn))
+	  {
+	    count_reg_usage (insn, counts, NULL_RTX, 1);
+	    note_stores (PATTERN (insn), count_stores, counts + nreg * 2);
+	  }
+      /* If there can be debug insns, COUNTS are 3 consecutive arrays.
+	 First one counts how many times each pseudo is used outside
+	 of debug insns, second counts how many times each pseudo is
+	 used in debug insns and third counts how many times a pseudo
+	 is stored.  */
+    }
+  else
+    {
+      counts = XCNEWVEC (int, nreg);
+      for (insn = insns; insn; insn = NEXT_INSN (insn))
+	if (INSN_P (insn))
+	  count_reg_usage (insn, counts, NULL_RTX, 1);
+      /* If no debug insns can be present, COUNTS is just an array
+	 which counts how many times each pseudo is used.  */
+    }
   /* Go from the last insn to the first and delete insns that only set unused
      registers or copy a register to itself.  As we delete an insn, remove
      usage counts for registers it uses.
 
      The first jump optimization pass may leave a real insn as the last
      insn in the function.   We must not skip that insn or we may end
-     up deleting code that is not really dead.  */
+     up deleting code that is not really dead.
+
+     If some otherwise unused register is only used in DEBUG_INSNs,
+     try to create a DEBUG_EXPR temporary and emit a DEBUG_INSN before
+     the setter.  Then go through DEBUG_INSNs and if a DEBUG_EXPR
+     has been created for the unused register, replace it with
+     the DEBUG_EXPR, otherwise reset the DEBUG_INSN.  */
   for (insn = get_last_insn (); insn; insn = prev)
     {
       int live_insn = 0;
@@ -6834,12 +6907,80 @@ delete_trivially_dead_insns (rtx insns, int nreg)
 
       if (! live_insn && dbg_cnt (delete_trivial_dead))
 	{
-	  count_reg_usage (insn, counts, NULL_RTX, -1);
+	  if (DEBUG_INSN_P (insn))
+	    count_reg_usage (INSN_VAR_LOCATION_LOC (insn), counts + nreg,
+			     NULL_RTX, -1);
+	  else
+	    {
+	      rtx set;
+	      if (MAY_HAVE_DEBUG_INSNS
+		  && (set = single_set (insn)) != NULL_RTX
+		  && is_dead_reg (SET_DEST (set), counts)
+		  /* Used at least once in some DEBUG_INSN.  */
+		  && counts[REGNO (SET_DEST (set)) + nreg] > 0
+		  /* And set exactly once.  */
+		  && counts[REGNO (SET_DEST (set)) + nreg * 2] == 1
+		  && !side_effects_p (SET_SRC (set))
+		  && asm_noperands (PATTERN (insn)) < 0)
+		{
+		  rtx dval, bind;
+
+		  /* Create DEBUG_EXPR (and DEBUG_EXPR_DECL).  */
+		  dval = make_debug_expr_from_rtl (SET_DEST (set));
+
+		  /* Emit a debug bind insn before the insn in which
+		     reg dies.  */
+		  bind = gen_rtx_VAR_LOCATION (GET_MODE (SET_DEST (set)),
+					       DEBUG_EXPR_TREE_DECL (dval),
+					       SET_SRC (set),
+					       VAR_INIT_STATUS_INITIALIZED);
+		  count_reg_usage (bind, counts + nreg, NULL_RTX, 1);
+
+		  bind = emit_debug_insn_before (bind, insn);
+		  df_insn_rescan (bind);
+
+		  if (replacements == NULL)
+		    replacements = XCNEWVEC (rtx, nreg);
+		  replacements[REGNO (SET_DEST (set))] = dval;
+		}
+
+	      count_reg_usage (insn, counts, NULL_RTX, -1);
+	      ndead++;
+	    }
 	  delete_insn_and_edges (insn);
-	  ndead++;
 	}
     }
 
+  if (MAY_HAVE_DEBUG_INSNS)
+    {
+      struct dead_debug_insn_data ddid;
+      ddid.counts = counts;
+      ddid.replacements = replacements;
+      for (insn = get_last_insn (); insn; insn = PREV_INSN (insn))
+	if (DEBUG_INSN_P (insn))
+	  {
+	    /* If this debug insn references a dead register that wasn't replaced
+	       with an DEBUG_EXPR, reset the DEBUG_INSN.  */
+	    ddid.seen_repl = false;
+	    if (for_each_rtx (&INSN_VAR_LOCATION_LOC (insn),
+			      is_dead_debug_insn, &ddid))
+	      {
+		INSN_VAR_LOCATION_LOC (insn) = gen_rtx_UNKNOWN_VAR_LOC ();
+		df_insn_rescan (insn);
+	      }
+	    else if (ddid.seen_repl)
+	      {
+		INSN_VAR_LOCATION_LOC (insn)
+		  = simplify_replace_fn_rtx (INSN_VAR_LOCATION_LOC (insn),
+					     NULL_RTX, replace_dead_reg,
+					     replacements);
+		df_insn_rescan (insn);
+	      }
+	  }
+      if (replacements)
+	free (replacements);
+    }
+
   if (dump_file && ndead)
     fprintf (dump_file, "Deleted %i trivially dead insns\n",
 	     ndead);