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diff --git a/gcc/inchash.h b/gcc/inchash.h
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+/* An incremental hash abstract data type.
+   Copyright (C) 2014 Free Software Foundation, Inc.
+
+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/>.  */
+
+#ifndef INCHASH_H
+#define INCHASH_H 1
+
+#include "config.h"
+#include "system.h"
+#include "coretypes.h"
+#include "hashtab.h"
+
+/* This file implements an incremential hash function ADT, to be used
+   by code that incrementially hashes a lot of unrelated data
+   (not in a single memory block) into a single value. The goal
+   is to make it easy to plug in efficient hash algorithms.
+   Currently it just implements the plain old jhash based
+   incremental hash from gcc's tree.c.  */
+
+extern hashval_t iterative_hash_host_wide_int (HOST_WIDE_INT, hashval_t);
+extern hashval_t iterative_hash_hashval_t (hashval_t, hashval_t);
+
+class inchash
+{
+ public:
+
+  /* Start incremential hashing, optionally with SEED.  */
+  inchash (hashval_t seed = 0)
+  {
+    val = seed;
+    bits = 0;
+  }
+
+  /* End incremential hashing and provide the final value.  */
+  hashval_t end ()
+  {
+    return val;
+  }
+
+  /* Add unsigned value V.  */
+  void add_int (unsigned v)
+  {
+    val = iterative_hash_hashval_t (v, val);
+  }
+
+  /* Add HOST_WIDE_INT value V.  */
+  void add_wide_int (HOST_WIDE_INT v)
+  {
+    val = iterative_hash_host_wide_int (v, val);
+  }
+
+  /* Hash in pointer PTR.  */
+  void add_ptr (void *ptr)
+  {
+    add (&ptr, sizeof (ptr));
+  }
+
+  /* Add a memory block DATA with size LEN.  */
+  void add (const void *data, size_t len)
+  {
+    val = iterative_hash (data, len, val);
+  }
+
+  /* Merge hash value OTHER.  */
+  void merge_hash (hashval_t other)
+  {
+    val = iterative_hash_hashval_t (other, val);
+  }
+
+  /* Hash in state from other inchash OTHER.  */
+  void merge (inchash &other)
+  {
+    merge_hash (other.val);
+  }
+
+  /* Support for accumulating boolean flags */
+
+  void add_flag (bool flag)
+  {
+    bits = (bits << 1) | flag;
+  }
+
+  void commit_flag ()
+  {
+    add_int (bits);
+    bits = 0;
+  }
+
+  /* Support for commutative hashing. Add A and B in a defined order
+     based on their value. This is useful for hashing commutative
+     expressions, so that A+B and B+A get the same hash.  */
+
+  void add_commutative (inchash &a, inchash &b)
+  {
+    if (a.end() > b.end())
+      {
+        merge (b);
+	merge (a);
+      }
+    else
+      {
+        merge (a);
+        merge (b);
+      }
+  }
+
+ private:
+  hashval_t val;
+  unsigned bits;
+};
+
+#define add_object(o) add (&(o), sizeof (o))
+
+#endif