Initial checkin of GCC 4.9.0 from trunk (r208799).

Change-Id: I48a3c08bb98542aa215912a75f03c0890e497dba

1 files changed, 220 insertions, 0 deletions

diff --git a/gcc-4.9/gcc/domwalk.c b/gcc-4.9/gcc/domwalk.c
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+/* Generic dominator tree walker
+   Copyright (C) 2003-2014 Free Software Foundation, Inc.
+   Contributed by Diego Novillo <dnovillo@redhat.com>
+
+This file is part of GCC.
+
+GCC is free software; you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation; either version 3, or (at your option)
+any later version.
+
+GCC is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with GCC; see the file COPYING3.  If not see
+<http://www.gnu.org/licenses/>.  */
+
+#include "config.h"
+#include "system.h"
+#include "coretypes.h"
+#include "tm.h"
+#include "basic-block.h"
+#include "domwalk.h"
+#include "sbitmap.h"
+
+/* This file implements a generic walker for dominator trees.
+
+  To understand the dominator walker one must first have a grasp of dominators,
+  immediate dominators and the dominator tree.
+
+  Dominators
+    A block B1 is said to dominate B2 if every path from the entry to B2 must
+    pass through B1.  Given the dominance relationship, we can proceed to
+    compute immediate dominators.  Note it is not important whether or not
+    our definition allows a block to dominate itself.
+
+  Immediate Dominators:
+    Every block in the CFG has no more than one immediate dominator.  The
+    immediate dominator of block BB must dominate BB and must not dominate
+    any other dominator of BB and must not be BB itself.
+
+  Dominator tree:
+    If we then construct a tree where each node is a basic block and there
+    is an edge from each block's immediate dominator to the block itself, then
+    we have a dominator tree.
+
+
+  [ Note this walker can also walk the post-dominator tree, which is
+    defined in a similar manner.  i.e., block B1 is said to post-dominate
+    block B2 if all paths from B2 to the exit block must pass through
+    B1.  ]
+
+  For example, given the CFG
+
+                   1
+                   |
+                   2
+                  / \
+                 3   4
+                    / \
+       +---------->5   6
+       |          / \ /
+       |    +--->8   7
+       |    |   /    |
+       |    +--9    11
+       |      /      |
+       +--- 10 ---> 12
+
+
+  We have a dominator tree which looks like
+
+                   1
+                   |
+                   2
+                  / \
+                 /   \
+                3     4
+                   / / \ \
+                   | | | |
+                   5 6 7 12
+                   |   |
+                   8   11
+                   |
+                   9
+                   |
+                  10
+
+
+
+  The dominator tree is the basis for a number of analysis, transformation
+  and optimization algorithms that operate on a semi-global basis.
+
+  The dominator walker is a generic routine which visits blocks in the CFG
+  via a depth first search of the dominator tree.  In the example above
+  the dominator walker might visit blocks in the following order
+  1, 2, 3, 4, 5, 8, 9, 10, 6, 7, 11, 12.
+
+  The dominator walker has a number of callbacks to perform actions
+  during the walk of the dominator tree.  There are two callbacks
+  which walk statements, one before visiting the dominator children,
+  one after visiting the dominator children.  There is a callback
+  before and after each statement walk callback.  In addition, the
+  dominator walker manages allocation/deallocation of data structures
+  which are local to each block visited.
+
+  The dominator walker is meant to provide a generic means to build a pass
+  which can analyze or transform/optimize a function based on walking
+  the dominator tree.  One simply fills in the dominator walker data
+  structure with the appropriate callbacks and calls the walker.
+
+  We currently use the dominator walker to prune the set of variables
+  which might need PHI nodes (which can greatly improve compile-time
+  performance in some cases).
+
+  We also use the dominator walker to rewrite the function into SSA form
+  which reduces code duplication since the rewriting phase is inherently
+  a walk of the dominator tree.
+
+  And (of course), we use the dominator walker to drive our dominator
+  optimizer, which is a semi-global optimizer.
+
+  TODO:
+
+    Walking statements is based on the block statement iterator abstraction,
+    which is currently an abstraction over walking tree statements.  Thus
+    the dominator walker is currently only useful for trees.  */
+
+static int *bb_postorder;
+
+static int
+cmp_bb_postorder (const void *a, const void *b)
+{
+  basic_block bb1 = *(basic_block *)const_cast<void *>(a);
+  basic_block bb2 = *(basic_block *)const_cast<void *>(b);
+  if (bb1->index == bb2->index)
+    return 0;
+  /* Place higher completion number first (pop off lower number first).  */
+  if (bb_postorder[bb1->index] > bb_postorder[bb2->index])
+    return -1;
+  return 1;
+}
+
+/* Recursively walk the dominator tree.
+   BB is the basic block we are currently visiting.  */
+
+void
+dom_walker::walk (basic_block bb)
+{
+  basic_block dest;
+  basic_block *worklist = XNEWVEC (basic_block,
+				   n_basic_blocks_for_fn (cfun) * 2);
+  int sp = 0;
+  int *postorder, postorder_num;
+
+  if (m_dom_direction == CDI_DOMINATORS)
+    {
+      postorder = XNEWVEC (int, n_basic_blocks_for_fn (cfun));
+      postorder_num = inverted_post_order_compute (postorder);
+      bb_postorder = XNEWVEC (int, last_basic_block_for_fn (cfun));
+      for (int i = 0; i < postorder_num; ++i)
+	bb_postorder[postorder[i]] = i;
+      free (postorder);
+    }
+
+  while (true)
+    {
+      /* Don't worry about unreachable blocks.  */
+      if (EDGE_COUNT (bb->preds) > 0
+	  || bb == ENTRY_BLOCK_PTR_FOR_FN (cfun)
+	  || bb == EXIT_BLOCK_PTR_FOR_FN (cfun))
+	{
+	  /* Callback for subclasses to do custom things before we have walked
+	     the dominator children, but before we walk statements.  */
+	  before_dom_children (bb);
+
+	  /* Mark the current BB to be popped out of the recursion stack
+	     once children are processed.  */
+	  worklist[sp++] = bb;
+	  worklist[sp++] = NULL;
+
+	  int saved_sp = sp;
+	  for (dest = first_dom_son (m_dom_direction, bb);
+	       dest; dest = next_dom_son (m_dom_direction, dest))
+	    worklist[sp++] = dest;
+	  if (m_dom_direction == CDI_DOMINATORS)
+	    switch (sp - saved_sp)
+	      {
+	      case 0:
+	      case 1:
+		break;
+	      default:
+		qsort (&worklist[saved_sp], sp - saved_sp,
+		       sizeof (basic_block), cmp_bb_postorder);
+	      }
+	}
+      /* NULL is used to mark pop operations in the recursion stack.  */
+      while (sp > 0 && !worklist[sp - 1])
+	{
+	  --sp;
+	  bb = worklist[--sp];
+
+	  /* Callback allowing subclasses to do custom things after we have
+	     walked dominator children, but before we walk statements.  */
+	  after_dom_children (bb);
+	}
+      if (sp)
+	bb = worklist[--sp];
+      else
+	break;
+    }
+  if (m_dom_direction == CDI_DOMINATORS)
+    {
+      free (bb_postorder);
+      bb_postorder = NULL;
+    }
+  free (worklist);
+}