1 /*
   2  * Copyright (c) 2014, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.
   8  *
   9  * This code is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
  14  *
  15  * You should have received a copy of the GNU General Public License version
  16  * 2 along with this work; if not, write to the Free Software Foundation,
  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18  *
  19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  20  * or visit www.oracle.com if you need additional information or have any
  21  * questions.
  22  *
  23  */
  24 
  25 #include "precompiled.hpp"
  26 #include "opto/loopnode.hpp"
  27 #include "opto/opaquenode.hpp"
  28 #include "opto/phaseX.hpp"
  29 
  30 //=============================================================================
  31 // Do not allow value-numbering
  32 uint Opaque1Node::hash() const { return NO_HASH; }
  33 uint Opaque1Node::cmp(const Node &n) const {
  34   return (&n == this);          // Always fail except on self
  35 }
  36 
  37 //------------------------------Identity---------------------------------------
  38 // If _major_progress, then more loop optimizations follow.  Do NOT remove
  39 // the opaque Node until no more loop ops can happen.  Note the timing of
  40 // _major_progress; it's set in the major loop optimizations THEN comes the
  41 // call to IterGVN and any chance of hitting this code.  Hence there's no
  42 // phase-ordering problem with stripping Opaque1 in IGVN followed by some
  43 // more loop optimizations that require it.
  44 Node *Opaque1Node::Identity(PhaseTransform *phase) {
  45   return phase->C->major_progress() ? this : in(1);
  46 }
  47 
  48 //=============================================================================
  49 // A node to prevent unwanted optimizations.  Allows constant folding.  Stops
  50 // value-numbering, most Ideal calls or Identity functions.  This Node is
  51 // specifically designed to prevent the pre-increment value of a loop trip
  52 // counter from being live out of the bottom of the loop (hence causing the
  53 // pre- and post-increment values both being live and thus requiring an extra
  54 // temp register and an extra move).  If we "accidentally" optimize through
  55 // this kind of a Node, we'll get slightly pessimal, but correct, code.  Thus
  56 // it's OK to be slightly sloppy on optimizations here.
  57 
  58 // Do not allow value-numbering
  59 uint Opaque2Node::hash() const { return NO_HASH; }
  60 uint Opaque2Node::cmp( const Node &n ) const {
  61   return (&n == this);          // Always fail except on self
  62 }
  63 
  64