view src/share/vm/opto/optoreg.hpp @ 2346:e1162778c1c8

7009266: G1: assert(obj->is_oop_or_null(true )) failed: Error Summary: A referent object that is only weakly reachable at the start of concurrent marking but is re-attached to the strongly reachable object graph during marking may not be marked as live. This can cause the reference object to be processed prematurely and leave dangling pointers to the referent object. Implement a read barrier for the java.lang.ref.Reference::referent field by intrinsifying the Reference.get() method, and intercepting accesses though JNI, reflection, and Unsafe, so that when a non-null referent object is read it is also logged in an SATB buffer. Reviewed-by: kvn, iveresov, never, tonyp, dholmes
author johnc
date Thu, 07 Apr 2011 09:53:20 -0700
parents c18cbe5936b8
children f6f3bb0ee072
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 * Copyright (c) 2006, 2010, Oracle and/or its affiliates. All rights reserved.
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.
 * This code 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
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit if you need additional information or have any
 * questions.


// We eventually need Registers for the Real World.  Registers are essentially
// non-SSA names.  A Register is represented as a number.  Non-regular values
// (e.g., Control, Memory, I/O) use the Special register.  The actual machine
// registers (as described in the ADL file for a machine) start at zero.
// Stack-slots (spill locations) start at the nest Chunk past the last machine
// register.
// Note that stack spill-slots are treated as a very large register set.
// They have all the correct properties for a Register: not aliased (unique
// named).  There is some simple mapping from a stack-slot register number
// to the actual location on the stack; this mapping depends on the calling
// conventions and is described in the ADL.
// Note that Name is not enum. C++ standard defines that the range of enum
// is the range of smallest bit-field that can represent all enumerators
// declared in the enum. The result of assigning a value to enum is undefined
// if the value is outside the enumeration's valid range. OptoReg::Name is
// typedef'ed as int, because it needs to be able to represent spill-slots.

 friend class C2Compiler;
  typedef int Name;
  enum {
    // Chunk 0
    Physical = AdlcVMDeps::Physical, // Start of physical regs
    // A few oddballs at the edge of the world
    Special = -2,               // All special (not allocated) values
    Bad = -1                    // Not a register


 static const VMReg opto2vm[REG_COUNT];
 static Name vm2opto[ConcreteRegisterImpl::number_of_registers];


  // Stack pointer register
  static OptoReg::Name c_frame_pointer;

  // Increment a register number.  As in:
  //    "for ( OptoReg::Name i; i=Control; i = add(i,1) ) ..."
  static Name add( Name x, int y ) { return Name(x+y); }

  // (We would like to have an operator+ for RegName, but it is not
  // a class, so this would be illegal in C++.)

  static void dump( int );

  // Get the stack slot number of an OptoReg::Name
  static unsigned int reg2stack( OptoReg::Name r) {
    assert( r >= stack0(), " must be");
    return r - stack0();

  // convert a stack slot number into an OptoReg::Name
  static OptoReg::Name stack2reg( int idx) {
    return Name(stack0() + idx);

  static bool is_stack(Name n) {
    return n >= stack0();

  static bool is_valid(Name n) {
    return (n != Bad);

  static bool is_reg(Name n) {
    return  is_valid(n) && !is_stack(n);

  static VMReg as_VMReg(OptoReg::Name n) {
    if (is_reg(n)) {
      // Must use table, it'd be nice if Bad was indexable...
      return opto2vm[n];
    } else {
      assert(!is_stack(n), "must un warp");
      return VMRegImpl::Bad();

  // Can un-warp a stack slot or convert a register or Bad
  static VMReg as_VMReg(OptoReg::Name n, int frame_size, int arg_count) {
    if (is_reg(n)) {
      // Must use table, it'd be nice if Bad was indexable...
      return opto2vm[n];
    } else if (is_stack(n)) {
      int stack_slot = reg2stack(n);
      if (stack_slot < arg_count) {
        return VMRegImpl::stack2reg(stack_slot + frame_size);
      return VMRegImpl::stack2reg(stack_slot - arg_count);
      // return return VMRegImpl::stack2reg(reg2stack(OptoReg::add(n, -arg_count)));
    } else {
      return VMRegImpl::Bad();

  static OptoReg::Name as_OptoReg(VMReg r) {
    if (r->is_stack()) {
      assert(false, "must warp");
      return stack2reg(r->reg2stack());
    } else if (r->is_valid()) {
      // Must use table, it'd be nice if Bad was indexable...
      return vm2opto[r->value()];
    } else {
      return Bad;

  static OptoReg::Name stack0() {
    return VMRegImpl::stack0->value();

  static const char* regname(OptoReg::Name n) {
    return as_VMReg(n)->name();


// Pairs of 32-bit registers for the allocator.
// This is a very similar class to VMRegPair. C2 only interfaces with VMRegPair
// via the calling convention code which is shared between the compilers.
// Since C2 uses OptoRegs for register allocation it is more efficient to use
// VMRegPair internally for nodes that can contain a pair of OptoRegs rather
// than use VMRegPair and continually be converting back and forth. So normally
// C2 will take in a VMRegPair from the calling convention code and immediately
// convert them to an OptoRegPair and stay in the OptoReg world. The only over
// conversion between OptoRegs and VMRegs is for debug info and oopMaps. This
// is not a high bandwidth spot and so it is not an issue.
// Note that onde other consequence of staying in the OptoReg world with OptoRegPairs
// is that there are "physical" OptoRegs that are not representable in the VMReg
// world, notably flags. [ But by design there is "space" in the VMReg world
// for such registers they just may not be concrete ]. So if we were to use VMRegPair
// then the VMReg world would have to have a representation for these registers
// so that a OptoReg->VMReg->OptoReg would reproduce ther original OptoReg. As it
// stands if you convert a flag (condition code) to a VMReg you will get VMRegImpl::Bad
// and converting that will return OptoReg::Bad losing the identity of the OptoReg.

class OptoRegPair {
  short _second;
  short _first;
  void set_bad (                   ) { _second = OptoReg::Bad; _first = OptoReg::Bad; }
  void set1    ( OptoReg::Name n  ) { _second = OptoReg::Bad; _first = n; }
  void set2    ( OptoReg::Name n  ) { _second = n + 1;       _first = n; }
  void set_pair( OptoReg::Name second, OptoReg::Name first    ) { _second= second;    _first= first; }
  void set_ptr ( OptoReg::Name ptr ) {
#ifdef _LP64
    _second = ptr+1;
    _second = OptoReg::Bad;
    _first = ptr;

  OptoReg::Name second() const { return _second; }
  OptoReg::Name first() const { return _first; }
  OptoRegPair(OptoReg::Name second, OptoReg::Name first) {  _second = second; _first = first; }
  OptoRegPair(OptoReg::Name f) { _second = OptoReg::Bad; _first = f; }
  OptoRegPair() { _second = OptoReg::Bad; _first = OptoReg::Bad; }