1 /*
   2  * Copyright (c) 1998, 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 "ci/ciMethod.hpp"
  27 #include "ci/ciMethodBlocks.hpp"
  28 #include "ci/ciStreams.hpp"
  29 #include "compiler/methodLiveness.hpp"
  30 #include "interpreter/bytecode.hpp"
  31 #include "interpreter/bytecodes.hpp"
  32 #include "memory/allocation.inline.hpp"

  33 #include "utilities/bitMap.inline.hpp"
  34 
  35 // The MethodLiveness class performs a simple liveness analysis on a method
  36 // in order to decide which locals are live (that is, will be used again) at
  37 // a particular bytecode index (bci).
  38 //
  39 // The algorithm goes:
  40 //
  41 // 1. Break the method into a set of basic blocks.  For each basic block we
  42 //    also keep track of its set of predecessors through normal control flow
  43 //    and predecessors through exceptional control flow.
  44 //
  45 // 2. For each basic block, compute two sets, gen (the set of values used before
  46 //    they are defined) and kill (the set of values defined before they are used)
  47 //    in the basic block.  A basic block "needs" the locals in its gen set to
  48 //    perform its computation.  A basic block "provides" values for the locals in
  49 //    its kill set, allowing a need from a successor to be ignored.
  50 //
  51 // 3. Liveness information (the set of locals which are needed) is pushed backwards through
  52 //    the program, from blocks to their predecessors.  We compute and store liveness

   1 /*
   2  * Copyright (c) 1998, 2016, 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 "ci/ciMethod.hpp"
  27 #include "ci/ciMethodBlocks.hpp"
  28 #include "ci/ciStreams.hpp"
  29 #include "compiler/methodLiveness.hpp"
  30 #include "interpreter/bytecode.hpp"
  31 #include "interpreter/bytecodes.hpp"
  32 #include "memory/allocation.inline.hpp"
  33 #include "memory/resourceArea.hpp"
  34 #include "utilities/bitMap.inline.hpp"
  35 
  36 // The MethodLiveness class performs a simple liveness analysis on a method
  37 // in order to decide which locals are live (that is, will be used again) at
  38 // a particular bytecode index (bci).
  39 //
  40 // The algorithm goes:
  41 //
  42 // 1. Break the method into a set of basic blocks.  For each basic block we
  43 //    also keep track of its set of predecessors through normal control flow
  44 //    and predecessors through exceptional control flow.
  45 //
  46 // 2. For each basic block, compute two sets, gen (the set of values used before
  47 //    they are defined) and kill (the set of values defined before they are used)
  48 //    in the basic block.  A basic block "needs" the locals in its gen set to
  49 //    perform its computation.  A basic block "provides" values for the locals in
  50 //    its kill set, allowing a need from a successor to be ignored.
  51 //
  52 // 3. Liveness information (the set of locals which are needed) is pushed backwards through
  53 //    the program, from blocks to their predecessors.  We compute and store liveness