src/hotspot/cpu/arm/c2_MacroAssembler_arm.cpp

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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * 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.
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#include "asm/assembler.hpp"
#include "asm/assembler.inline.hpp"
#include "opto/c2_MacroAssembler.hpp"
#include "runtime/basicLock.hpp"

// TODO: 8 bytes at a time? pre-fetch?
// Compare char[] arrays aligned to 4 bytes.
void C2_MacroAssembler::char_arrays_equals(Register ary1, Register ary2,
                                           Register limit, Register result,
                                           Register chr1, Register chr2, Label& Ldone) {
  Label Lvector, Lloop;

  // if (ary1 == ary2)
  //     return true;
  cmpoop(ary1, ary2);
  b(Ldone, eq);

  // Note: limit contains number of bytes (2*char_elements) != 0.
  tst(limit, 0x2); // trailing character ?
  b(Lvector, eq);

  // compare the trailing char
  sub(limit, limit, sizeof(jchar));
  ldrh(chr1, Address(ary1, limit));
  ldrh(chr2, Address(ary2, limit));
  cmp(chr1, chr2);
  mov(result, 0, ne);     // not equal
  b(Ldone, ne);

  // only one char ?
  tst(limit, limit);
  mov(result, 1, eq);
  b(Ldone, eq);

  // word by word compare, don't need alignment check
  bind(Lvector);

  // Shift ary1 and ary2 to the end of the arrays, negate limit
  add(ary1, limit, ary1);
  add(ary2, limit, ary2);
  neg(limit, limit);

  bind(Lloop);
  ldr_u32(chr1, Address(ary1, limit));
  ldr_u32(chr2, Address(ary2, limit));
  cmp_32(chr1, chr2);
  mov(result, 0, ne);     // not equal
  b(Ldone, ne);
  adds(limit, limit, 2*sizeof(jchar));
  b(Lloop, ne);

  // Caller should set it:
  // mov(result_reg, 1);  //equal
}

void C2_MacroAssembler::fast_lock(Register Roop, Register Rbox, Register Rscratch, Register Rscratch2) {
  assert(VM_Version::supports_ldrex(), "unsupported, yet?");
  assert_different_registers(Roop, Rbox, Rscratch, Rscratch2);

  Label fast_lock, done;

  if (DiagnoseSyncOnValueBasedClasses != 0) {
    load_klass(Rscratch, Roop);
    ldrb(Rscratch, Address(Rscratch, Klass::misc_flags_offset()));
    tst(Rscratch, KlassFlags::_misc_is_value_based_class);
    b(done, ne);
  }

  if (LockingMode == LM_LIGHTWEIGHT) {

    lightweight_lock(Roop /* obj */, Rbox /* t1 */, Rscratch /* t2 */, Rscratch2 /* t3 */,
                     1 /* savemask (save t1) */, done);

    // Success: set Z
    cmp(Roop, Roop);

  } else if (LockingMode == LM_LEGACY) {

    Register Rmark      = Rscratch2;

    ldr(Rmark, Address(Roop, oopDesc::mark_offset_in_bytes()));
    tst(Rmark, markWord::unlocked_value);
    b(fast_lock, ne);

    // Check for recursive lock
    // See comments in InterpreterMacroAssembler::lock_object for
    // explanations on the fast recursive locking check.
    // -1- test low 2 bits
    movs(Rscratch, AsmOperand(Rmark, lsl, 30));
    // -2- test (hdr - SP) if the low two bits are 0
    sub(Rscratch, Rmark, SP, eq);
    movs(Rscratch, AsmOperand(Rscratch, lsr, exact_log2(os::vm_page_size())), eq);
    // If still 'eq' then recursive locking OK
    // set to zero if recursive lock, set to non zero otherwise (see discussion in JDK-8153107)
    str(Rscratch, Address(Rbox, BasicLock::displaced_header_offset_in_bytes()));
    b(done);

    bind(fast_lock);
    str(Rmark, Address(Rbox, BasicLock::displaced_header_offset_in_bytes()));

    bool allow_fallthrough_on_failure = true;
    bool one_shot = true;
    cas_for_lock_acquire(Rmark, Rbox, Roop, Rscratch, done, allow_fallthrough_on_failure, one_shot);
  }

  bind(done);

  // At this point flags are set as follows:
  //  EQ -> Success
  //  NE -> Failure, branch to slow path
}

void C2_MacroAssembler::fast_unlock(Register Roop, Register Rbox, Register Rscratch, Register Rscratch2) {
  assert(VM_Version::supports_ldrex(), "unsupported, yet?");
  assert_different_registers(Roop, Rbox, Rscratch, Rscratch2);

  Label done;

  if (LockingMode == LM_LIGHTWEIGHT) {

    lightweight_unlock(Roop /* obj */, Rbox /* t1 */, Rscratch /* t2 */, Rscratch2 /* t3 */,
                       1 /* savemask (save t1) */, done);

    cmp(Roop, Roop); // Success: Set Z
    // Fall through

  } else if (LockingMode == LM_LEGACY) {

    Register Rmark      = Rscratch2;

    // Find the lock address and load the displaced header from the stack.
    ldr(Rmark, Address(Rbox, BasicLock::displaced_header_offset_in_bytes()));
    // If hdr is null, we've got recursive locking and there's nothing more to do
    cmp(Rmark, 0);
    b(done, eq);

    // Restore the object header
    bool allow_fallthrough_on_failure = true;
    bool one_shot = true;
    cas_for_lock_release(Rbox, Rmark, Roop, Rscratch, done, allow_fallthrough_on_failure, one_shot);
  }
  bind(done);

  // At this point flags are set as follows:
  //  EQ -> Success
  //  NE -> Failure, branch to slow path
}