re PR tree-optimization/26251 (code size increase with -Os)

	PR tree-optimization/26251
	* tree-ssa-threadupdate.c (redirection_block_p): New function.
	(thread_block): When optimizing for size refuse to thread jumps
	that would require duplication of blocks other than redirection
	blocks.

From-SVN: r115150

gcc/ChangeLog

+2006-07-03  Roger Sayle  <roger@eyesopen.com>
+
+	PR tree-optimization/26251
+	* tree-ssa-threadupdate.c (redirection_block_p): New function.
+	(thread_block): When optimizing for size refuse to thread jumps
+	that would require duplication of blocks other than redirection
+	blocks.
+
 2006-07-03  Paolo Bonzini  <bonzini@gnu.org>
 
 	* configure.ac: Fix thinko in previous check-in.

gcc/tree-ssa-threadupdate.c

 /* Thread edges through blocks and update the control flow and SSA graphs.
-   Copyright (C) 2004, 2005 Free Software Foundation, Inc.
+   Copyright (C) 2004, 2005, 2006 Free Software Foundation, Inc.
 
 This file is part of GCC.
 
@@ -652,6 +652,33 @@ redirect_edges (void **slot, void *data)
   return 1;
 }
 
+/* Return true if this block has no executable statements other than
+   a simple ctrl flow instruction.  When the number of outgoing edges
+   is one, this is equivalent to a "forwarder" block.  */
+
+static bool
+redirection_block_p (basic_block bb)
+{
+  block_stmt_iterator bsi;
+
+  /* Advance to the first executable statement.  */
+  bsi = bsi_start (bb);
+  while (!bsi_end_p (bsi)
+          && (TREE_CODE (bsi_stmt (bsi)) == LABEL_EXPR
+              || IS_EMPTY_STMT (bsi_stmt (bsi))))
+    bsi_next (&bsi);
+
+  /* Check if this is an empty block.  */
+  if (bsi_end_p (bsi))
+    return true;
+
+  /* Test that we've reached the terminating control statement.  */
+  return bsi_stmt (bsi)
+	 && (TREE_CODE (bsi_stmt (bsi)) == COND_EXPR
+	     || TREE_CODE (bsi_stmt (bsi)) == GOTO_EXPR
+	     || TREE_CODE (bsi_stmt (bsi)) == SWITCH_EXPR);
+}
+
 /* BB is a block which ends with a COND_EXPR or SWITCH_EXPR and when BB
    is reached via one or more specific incoming edges, we know which
    outgoing edge from BB will be traversed.
@@ -699,6 +726,17 @@ thread_block (basic_block bb)
      be threaded to a duplicate of BB.  */
   bool all = true;
 
+  /* If optimizing for size, only thread this block if we don't have
+     to duplicate it or it's an otherwise empty redirection block.  */
+  if (optimize_size
+      && EDGE_COUNT (bb->preds) > 1
+      && !redirection_block_p (bb))
+    {
+      FOR_EACH_EDGE (e, ei, bb->preds)
+	e->aux = NULL;
+      return false;
+    }
+
   /* To avoid scanning a linear array for the element we need we instead
      use a hash table.  For normal code there should be no noticeable
      difference.  However, if we have a block with a large number of