hotspot/src/cpu/ppc/vm/interpreter_ppc.cpp
changeset 35479 62c12ca7a45e
parent 35474 8333d76c7fee
child 35480 6ed8e1b70803
equal deleted inserted replaced
35474:8333d76c7fee 35479:62c12ca7a45e
     1 /*
       
     2  * Copyright (c) 1997, 2015, Oracle and/or its affiliates. All rights reserved.
       
     3  * Copyright 2012, 2015 SAP AG. All rights reserved.
       
     4  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
       
     5  *
       
     6  * This code is free software; you can redistribute it and/or modify it
       
     7  * under the terms of the GNU General Public License version 2 only, as
       
     8  * published by the Free Software Foundation.
       
     9  *
       
    10  * This code is distributed in the hope that it will be useful, but WITHOUT
       
    11  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
       
    12  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
       
    13  * version 2 for more details (a copy is included in the LICENSE file that
       
    14  * accompanied this code).
       
    15  *
       
    16  * You should have received a copy of the GNU General Public License version
       
    17  * 2 along with this work; if not, write to the Free Software Foundation,
       
    18  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
       
    19  *
       
    20  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
       
    21  * or visit www.oracle.com if you need additional information or have any
       
    22  * questions.
       
    23  *
       
    24  */
       
    25 
       
    26 #include "precompiled.hpp"
       
    27 #include "asm/macroAssembler.inline.hpp"
       
    28 #include "interpreter/bytecodeHistogram.hpp"
       
    29 #include "interpreter/interpreter.hpp"
       
    30 #include "interpreter/interpreterRuntime.hpp"
       
    31 #include "interpreter/interp_masm.hpp"
       
    32 #include "interpreter/templateInterpreterGenerator.hpp"
       
    33 #include "interpreter/templateTable.hpp"
       
    34 #include "oops/arrayOop.hpp"
       
    35 #include "oops/methodData.hpp"
       
    36 #include "oops/method.hpp"
       
    37 #include "oops/oop.inline.hpp"
       
    38 #include "prims/jvmtiExport.hpp"
       
    39 #include "prims/jvmtiThreadState.hpp"
       
    40 #include "prims/methodHandles.hpp"
       
    41 #include "runtime/arguments.hpp"
       
    42 #include "runtime/frame.inline.hpp"
       
    43 #include "runtime/sharedRuntime.hpp"
       
    44 #include "runtime/stubRoutines.hpp"
       
    45 #include "runtime/synchronizer.hpp"
       
    46 #include "runtime/timer.hpp"
       
    47 #include "runtime/vframeArray.hpp"
       
    48 #include "utilities/debug.hpp"
       
    49 #ifdef COMPILER1
       
    50 #include "c1/c1_Runtime1.hpp"
       
    51 #endif
       
    52 
       
    53 #define __ _masm->
       
    54 
       
    55 #ifdef PRODUCT
       
    56 #define BLOCK_COMMENT(str) // nothing
       
    57 #else
       
    58 #define BLOCK_COMMENT(str) __ block_comment(str)
       
    59 #endif
       
    60 
       
    61 #define BIND(label) bind(label); BLOCK_COMMENT(#label ":")
       
    62 
       
    63 address AbstractInterpreterGenerator::generate_slow_signature_handler() {
       
    64   // Slow_signature handler that respects the PPC C calling conventions.
       
    65   //
       
    66   // We get called by the native entry code with our output register
       
    67   // area == 8. First we call InterpreterRuntime::get_result_handler
       
    68   // to copy the pointer to the signature string temporarily to the
       
    69   // first C-argument and to return the result_handler in
       
    70   // R3_RET. Since native_entry will copy the jni-pointer to the
       
    71   // first C-argument slot later on, it is OK to occupy this slot
       
    72   // temporarilly. Then we copy the argument list on the java
       
    73   // expression stack into native varargs format on the native stack
       
    74   // and load arguments into argument registers. Integer arguments in
       
    75   // the varargs vector will be sign-extended to 8 bytes.
       
    76   //
       
    77   // On entry:
       
    78   //   R3_ARG1        - intptr_t*     Address of java argument list in memory.
       
    79   //   R15_prev_state - BytecodeInterpreter* Address of interpreter state for
       
    80   //     this method
       
    81   //   R19_method
       
    82   //
       
    83   // On exit (just before return instruction):
       
    84   //   R3_RET            - contains the address of the result_handler.
       
    85   //   R4_ARG2           - is not updated for static methods and contains "this" otherwise.
       
    86   //   R5_ARG3-R10_ARG8: - When the (i-2)th Java argument is not of type float or double,
       
    87   //                       ARGi contains this argument. Otherwise, ARGi is not updated.
       
    88   //   F1_ARG1-F13_ARG13 - contain the first 13 arguments of type float or double.
       
    89 
       
    90   const int LogSizeOfTwoInstructions = 3;
       
    91 
       
    92   // FIXME: use Argument:: GL: Argument names different numbers!
       
    93   const int max_fp_register_arguments  = 13;
       
    94   const int max_int_register_arguments = 6;  // first 2 are reserved
       
    95 
       
    96   const Register arg_java       = R21_tmp1;
       
    97   const Register arg_c          = R22_tmp2;
       
    98   const Register signature      = R23_tmp3;  // is string
       
    99   const Register sig_byte       = R24_tmp4;
       
   100   const Register fpcnt          = R25_tmp5;
       
   101   const Register argcnt         = R26_tmp6;
       
   102   const Register intSlot        = R27_tmp7;
       
   103   const Register target_sp      = R28_tmp8;
       
   104   const FloatRegister floatSlot = F0;
       
   105 
       
   106   address entry = __ function_entry();
       
   107 
       
   108   __ save_LR_CR(R0);
       
   109   __ save_nonvolatile_gprs(R1_SP, _spill_nonvolatiles_neg(r14));
       
   110   // We use target_sp for storing arguments in the C frame.
       
   111   __ mr(target_sp, R1_SP);
       
   112   __ push_frame_reg_args_nonvolatiles(0, R11_scratch1);
       
   113 
       
   114   __ mr(arg_java, R3_ARG1);
       
   115 
       
   116   __ call_VM_leaf(CAST_FROM_FN_PTR(address, InterpreterRuntime::get_signature), R16_thread, R19_method);
       
   117 
       
   118   // Signature is in R3_RET. Signature is callee saved.
       
   119   __ mr(signature, R3_RET);
       
   120 
       
   121   // Get the result handler.
       
   122   __ call_VM_leaf(CAST_FROM_FN_PTR(address, InterpreterRuntime::get_result_handler), R16_thread, R19_method);
       
   123 
       
   124   {
       
   125     Label L;
       
   126     // test if static
       
   127     // _access_flags._flags must be at offset 0.
       
   128     // TODO PPC port: requires change in shared code.
       
   129     //assert(in_bytes(AccessFlags::flags_offset()) == 0,
       
   130     //       "MethodDesc._access_flags == MethodDesc._access_flags._flags");
       
   131     // _access_flags must be a 32 bit value.
       
   132     assert(sizeof(AccessFlags) == 4, "wrong size");
       
   133     __ lwa(R11_scratch1/*access_flags*/, method_(access_flags));
       
   134     // testbit with condition register.
       
   135     __ testbitdi(CCR0, R0, R11_scratch1/*access_flags*/, JVM_ACC_STATIC_BIT);
       
   136     __ btrue(CCR0, L);
       
   137     // For non-static functions, pass "this" in R4_ARG2 and copy it
       
   138     // to 2nd C-arg slot.
       
   139     // We need to box the Java object here, so we use arg_java
       
   140     // (address of current Java stack slot) as argument and don't
       
   141     // dereference it as in case of ints, floats, etc.
       
   142     __ mr(R4_ARG2, arg_java);
       
   143     __ addi(arg_java, arg_java, -BytesPerWord);
       
   144     __ std(R4_ARG2, _abi(carg_2), target_sp);
       
   145     __ bind(L);
       
   146   }
       
   147 
       
   148   // Will be incremented directly after loop_start. argcnt=0
       
   149   // corresponds to 3rd C argument.
       
   150   __ li(argcnt, -1);
       
   151   // arg_c points to 3rd C argument
       
   152   __ addi(arg_c, target_sp, _abi(carg_3));
       
   153   // no floating-point args parsed so far
       
   154   __ li(fpcnt, 0);
       
   155 
       
   156   Label move_intSlot_to_ARG, move_floatSlot_to_FARG;
       
   157   Label loop_start, loop_end;
       
   158   Label do_int, do_long, do_float, do_double, do_dontreachhere, do_object, do_array, do_boxed;
       
   159 
       
   160   // signature points to '(' at entry
       
   161 #ifdef ASSERT
       
   162   __ lbz(sig_byte, 0, signature);
       
   163   __ cmplwi(CCR0, sig_byte, '(');
       
   164   __ bne(CCR0, do_dontreachhere);
       
   165 #endif
       
   166 
       
   167   __ bind(loop_start);
       
   168 
       
   169   __ addi(argcnt, argcnt, 1);
       
   170   __ lbzu(sig_byte, 1, signature);
       
   171 
       
   172   __ cmplwi(CCR0, sig_byte, ')'); // end of signature
       
   173   __ beq(CCR0, loop_end);
       
   174 
       
   175   __ cmplwi(CCR0, sig_byte, 'B'); // byte
       
   176   __ beq(CCR0, do_int);
       
   177 
       
   178   __ cmplwi(CCR0, sig_byte, 'C'); // char
       
   179   __ beq(CCR0, do_int);
       
   180 
       
   181   __ cmplwi(CCR0, sig_byte, 'D'); // double
       
   182   __ beq(CCR0, do_double);
       
   183 
       
   184   __ cmplwi(CCR0, sig_byte, 'F'); // float
       
   185   __ beq(CCR0, do_float);
       
   186 
       
   187   __ cmplwi(CCR0, sig_byte, 'I'); // int
       
   188   __ beq(CCR0, do_int);
       
   189 
       
   190   __ cmplwi(CCR0, sig_byte, 'J'); // long
       
   191   __ beq(CCR0, do_long);
       
   192 
       
   193   __ cmplwi(CCR0, sig_byte, 'S'); // short
       
   194   __ beq(CCR0, do_int);
       
   195 
       
   196   __ cmplwi(CCR0, sig_byte, 'Z'); // boolean
       
   197   __ beq(CCR0, do_int);
       
   198 
       
   199   __ cmplwi(CCR0, sig_byte, 'L'); // object
       
   200   __ beq(CCR0, do_object);
       
   201 
       
   202   __ cmplwi(CCR0, sig_byte, '['); // array
       
   203   __ beq(CCR0, do_array);
       
   204 
       
   205   //  __ cmplwi(CCR0, sig_byte, 'V'); // void cannot appear since we do not parse the return type
       
   206   //  __ beq(CCR0, do_void);
       
   207 
       
   208   __ bind(do_dontreachhere);
       
   209 
       
   210   __ unimplemented("ShouldNotReachHere in slow_signature_handler", 120);
       
   211 
       
   212   __ bind(do_array);
       
   213 
       
   214   {
       
   215     Label start_skip, end_skip;
       
   216 
       
   217     __ bind(start_skip);
       
   218     __ lbzu(sig_byte, 1, signature);
       
   219     __ cmplwi(CCR0, sig_byte, '[');
       
   220     __ beq(CCR0, start_skip); // skip further brackets
       
   221     __ cmplwi(CCR0, sig_byte, '9');
       
   222     __ bgt(CCR0, end_skip);   // no optional size
       
   223     __ cmplwi(CCR0, sig_byte, '0');
       
   224     __ bge(CCR0, start_skip); // skip optional size
       
   225     __ bind(end_skip);
       
   226 
       
   227     __ cmplwi(CCR0, sig_byte, 'L');
       
   228     __ beq(CCR0, do_object);  // for arrays of objects, the name of the object must be skipped
       
   229     __ b(do_boxed);          // otherwise, go directly to do_boxed
       
   230   }
       
   231 
       
   232   __ bind(do_object);
       
   233   {
       
   234     Label L;
       
   235     __ bind(L);
       
   236     __ lbzu(sig_byte, 1, signature);
       
   237     __ cmplwi(CCR0, sig_byte, ';');
       
   238     __ bne(CCR0, L);
       
   239    }
       
   240   // Need to box the Java object here, so we use arg_java (address of
       
   241   // current Java stack slot) as argument and don't dereference it as
       
   242   // in case of ints, floats, etc.
       
   243   Label do_null;
       
   244   __ bind(do_boxed);
       
   245   __ ld(R0,0, arg_java);
       
   246   __ cmpdi(CCR0, R0, 0);
       
   247   __ li(intSlot,0);
       
   248   __ beq(CCR0, do_null);
       
   249   __ mr(intSlot, arg_java);
       
   250   __ bind(do_null);
       
   251   __ std(intSlot, 0, arg_c);
       
   252   __ addi(arg_java, arg_java, -BytesPerWord);
       
   253   __ addi(arg_c, arg_c, BytesPerWord);
       
   254   __ cmplwi(CCR0, argcnt, max_int_register_arguments);
       
   255   __ blt(CCR0, move_intSlot_to_ARG);
       
   256   __ b(loop_start);
       
   257 
       
   258   __ bind(do_int);
       
   259   __ lwa(intSlot, 0, arg_java);
       
   260   __ std(intSlot, 0, arg_c);
       
   261   __ addi(arg_java, arg_java, -BytesPerWord);
       
   262   __ addi(arg_c, arg_c, BytesPerWord);
       
   263   __ cmplwi(CCR0, argcnt, max_int_register_arguments);
       
   264   __ blt(CCR0, move_intSlot_to_ARG);
       
   265   __ b(loop_start);
       
   266 
       
   267   __ bind(do_long);
       
   268   __ ld(intSlot, -BytesPerWord, arg_java);
       
   269   __ std(intSlot, 0, arg_c);
       
   270   __ addi(arg_java, arg_java, - 2 * BytesPerWord);
       
   271   __ addi(arg_c, arg_c, BytesPerWord);
       
   272   __ cmplwi(CCR0, argcnt, max_int_register_arguments);
       
   273   __ blt(CCR0, move_intSlot_to_ARG);
       
   274   __ b(loop_start);
       
   275 
       
   276   __ bind(do_float);
       
   277   __ lfs(floatSlot, 0, arg_java);
       
   278 #if defined(LINUX)
       
   279   // Linux uses ELF ABI. Both original ELF and ELFv2 ABIs have float
       
   280   // in the least significant word of an argument slot.
       
   281 #if defined(VM_LITTLE_ENDIAN)
       
   282   __ stfs(floatSlot, 0, arg_c);
       
   283 #else
       
   284   __ stfs(floatSlot, 4, arg_c);
       
   285 #endif
       
   286 #elif defined(AIX)
       
   287   // Although AIX runs on big endian CPU, float is in most significant
       
   288   // word of an argument slot.
       
   289   __ stfs(floatSlot, 0, arg_c);
       
   290 #else
       
   291 #error "unknown OS"
       
   292 #endif
       
   293   __ addi(arg_java, arg_java, -BytesPerWord);
       
   294   __ addi(arg_c, arg_c, BytesPerWord);
       
   295   __ cmplwi(CCR0, fpcnt, max_fp_register_arguments);
       
   296   __ blt(CCR0, move_floatSlot_to_FARG);
       
   297   __ b(loop_start);
       
   298 
       
   299   __ bind(do_double);
       
   300   __ lfd(floatSlot, - BytesPerWord, arg_java);
       
   301   __ stfd(floatSlot, 0, arg_c);
       
   302   __ addi(arg_java, arg_java, - 2 * BytesPerWord);
       
   303   __ addi(arg_c, arg_c, BytesPerWord);
       
   304   __ cmplwi(CCR0, fpcnt, max_fp_register_arguments);
       
   305   __ blt(CCR0, move_floatSlot_to_FARG);
       
   306   __ b(loop_start);
       
   307 
       
   308   __ bind(loop_end);
       
   309 
       
   310   __ pop_frame();
       
   311   __ restore_nonvolatile_gprs(R1_SP, _spill_nonvolatiles_neg(r14));
       
   312   __ restore_LR_CR(R0);
       
   313 
       
   314   __ blr();
       
   315 
       
   316   Label move_int_arg, move_float_arg;
       
   317   __ bind(move_int_arg); // each case must consist of 2 instructions (otherwise adapt LogSizeOfTwoInstructions)
       
   318   __ mr(R5_ARG3, intSlot);  __ b(loop_start);
       
   319   __ mr(R6_ARG4, intSlot);  __ b(loop_start);
       
   320   __ mr(R7_ARG5, intSlot);  __ b(loop_start);
       
   321   __ mr(R8_ARG6, intSlot);  __ b(loop_start);
       
   322   __ mr(R9_ARG7, intSlot);  __ b(loop_start);
       
   323   __ mr(R10_ARG8, intSlot); __ b(loop_start);
       
   324 
       
   325   __ bind(move_float_arg); // each case must consist of 2 instructions (otherwise adapt LogSizeOfTwoInstructions)
       
   326   __ fmr(F1_ARG1, floatSlot);   __ b(loop_start);
       
   327   __ fmr(F2_ARG2, floatSlot);   __ b(loop_start);
       
   328   __ fmr(F3_ARG3, floatSlot);   __ b(loop_start);
       
   329   __ fmr(F4_ARG4, floatSlot);   __ b(loop_start);
       
   330   __ fmr(F5_ARG5, floatSlot);   __ b(loop_start);
       
   331   __ fmr(F6_ARG6, floatSlot);   __ b(loop_start);
       
   332   __ fmr(F7_ARG7, floatSlot);   __ b(loop_start);
       
   333   __ fmr(F8_ARG8, floatSlot);   __ b(loop_start);
       
   334   __ fmr(F9_ARG9, floatSlot);   __ b(loop_start);
       
   335   __ fmr(F10_ARG10, floatSlot); __ b(loop_start);
       
   336   __ fmr(F11_ARG11, floatSlot); __ b(loop_start);
       
   337   __ fmr(F12_ARG12, floatSlot); __ b(loop_start);
       
   338   __ fmr(F13_ARG13, floatSlot); __ b(loop_start);
       
   339 
       
   340   __ bind(move_intSlot_to_ARG);
       
   341   __ sldi(R0, argcnt, LogSizeOfTwoInstructions);
       
   342   __ load_const(R11_scratch1, move_int_arg); // Label must be bound here.
       
   343   __ add(R11_scratch1, R0, R11_scratch1);
       
   344   __ mtctr(R11_scratch1/*branch_target*/);
       
   345   __ bctr();
       
   346   __ bind(move_floatSlot_to_FARG);
       
   347   __ sldi(R0, fpcnt, LogSizeOfTwoInstructions);
       
   348   __ addi(fpcnt, fpcnt, 1);
       
   349   __ load_const(R11_scratch1, move_float_arg); // Label must be bound here.
       
   350   __ add(R11_scratch1, R0, R11_scratch1);
       
   351   __ mtctr(R11_scratch1/*branch_target*/);
       
   352   __ bctr();
       
   353 
       
   354   return entry;
       
   355 }
       
   356 
       
   357 address AbstractInterpreterGenerator::generate_result_handler_for(BasicType type) {
       
   358   //
       
   359   // Registers alive
       
   360   //   R3_RET
       
   361   //   LR
       
   362   //
       
   363   // Registers updated
       
   364   //   R3_RET
       
   365   //
       
   366 
       
   367   Label done;
       
   368   address entry = __ pc();
       
   369 
       
   370   switch (type) {
       
   371   case T_BOOLEAN:
       
   372     // convert !=0 to 1
       
   373     __ neg(R0, R3_RET);
       
   374     __ orr(R0, R3_RET, R0);
       
   375     __ srwi(R3_RET, R0, 31);
       
   376     break;
       
   377   case T_BYTE:
       
   378      // sign extend 8 bits
       
   379      __ extsb(R3_RET, R3_RET);
       
   380      break;
       
   381   case T_CHAR:
       
   382      // zero extend 16 bits
       
   383      __ clrldi(R3_RET, R3_RET, 48);
       
   384      break;
       
   385   case T_SHORT:
       
   386      // sign extend 16 bits
       
   387      __ extsh(R3_RET, R3_RET);
       
   388      break;
       
   389   case T_INT:
       
   390      // sign extend 32 bits
       
   391      __ extsw(R3_RET, R3_RET);
       
   392      break;
       
   393   case T_LONG:
       
   394      break;
       
   395   case T_OBJECT:
       
   396     // unbox result if not null
       
   397     __ cmpdi(CCR0, R3_RET, 0);
       
   398     __ beq(CCR0, done);
       
   399     __ ld(R3_RET, 0, R3_RET);
       
   400     __ verify_oop(R3_RET);
       
   401     break;
       
   402   case T_FLOAT:
       
   403      break;
       
   404   case T_DOUBLE:
       
   405      break;
       
   406   case T_VOID:
       
   407      break;
       
   408   default: ShouldNotReachHere();
       
   409   }
       
   410 
       
   411   __ BIND(done);
       
   412   __ blr();
       
   413 
       
   414   return entry;
       
   415 }
       
   416 
       
   417 // Abstract method entry.
       
   418 //
       
   419 address TemplateInterpreterGenerator::generate_abstract_entry(void) {
       
   420   address entry = __ pc();
       
   421 
       
   422   //
       
   423   // Registers alive
       
   424   //   R16_thread     - JavaThread*
       
   425   //   R19_method     - callee's method (method to be invoked)
       
   426   //   R1_SP          - SP prepared such that caller's outgoing args are near top
       
   427   //   LR             - return address to caller
       
   428   //
       
   429   // Stack layout at this point:
       
   430   //
       
   431   //   0       [TOP_IJAVA_FRAME_ABI]         <-- R1_SP
       
   432   //           alignment (optional)
       
   433   //           [outgoing Java arguments]
       
   434   //           ...
       
   435   //   PARENT  [PARENT_IJAVA_FRAME_ABI]
       
   436   //            ...
       
   437   //
       
   438 
       
   439   // Can't use call_VM here because we have not set up a new
       
   440   // interpreter state. Make the call to the vm and make it look like
       
   441   // our caller set up the JavaFrameAnchor.
       
   442   __ set_top_ijava_frame_at_SP_as_last_Java_frame(R1_SP, R12_scratch2/*tmp*/);
       
   443 
       
   444   // Push a new C frame and save LR.
       
   445   __ save_LR_CR(R0);
       
   446   __ push_frame_reg_args(0, R11_scratch1);
       
   447 
       
   448   // This is not a leaf but we have a JavaFrameAnchor now and we will
       
   449   // check (create) exceptions afterward so this is ok.
       
   450   __ call_VM_leaf(CAST_FROM_FN_PTR(address, InterpreterRuntime::throw_AbstractMethodError),
       
   451                   R16_thread);
       
   452 
       
   453   // Pop the C frame and restore LR.
       
   454   __ pop_frame();
       
   455   __ restore_LR_CR(R0);
       
   456 
       
   457   // Reset JavaFrameAnchor from call_VM_leaf above.
       
   458   __ reset_last_Java_frame();
       
   459 
       
   460   // We don't know our caller, so jump to the general forward exception stub,
       
   461   // which will also pop our full frame off. Satisfy the interface of
       
   462   // SharedRuntime::generate_forward_exception()
       
   463   __ load_const_optimized(R11_scratch1, StubRoutines::forward_exception_entry(), R0);
       
   464   __ mtctr(R11_scratch1);
       
   465   __ bctr();
       
   466 
       
   467   return entry;
       
   468 }
       
   469 
       
   470 // Interpreter intrinsic for WeakReference.get().
       
   471 // 1. Don't push a full blown frame and go on dispatching, but fetch the value
       
   472 //    into R8 and return quickly
       
   473 // 2. If G1 is active we *must* execute this intrinsic for corrrectness:
       
   474 //    It contains a GC barrier which puts the reference into the satb buffer
       
   475 //    to indicate that someone holds a strong reference to the object the
       
   476 //    weak ref points to!
       
   477 address TemplateInterpreterGenerator::generate_Reference_get_entry(void) {
       
   478   // Code: _aload_0, _getfield, _areturn
       
   479   // parameter size = 1
       
   480   //
       
   481   // The code that gets generated by this routine is split into 2 parts:
       
   482   //    1. the "intrinsified" code for G1 (or any SATB based GC),
       
   483   //    2. the slow path - which is an expansion of the regular method entry.
       
   484   //
       
   485   // Notes:
       
   486   // * In the G1 code we do not check whether we need to block for
       
   487   //   a safepoint. If G1 is enabled then we must execute the specialized
       
   488   //   code for Reference.get (except when the Reference object is null)
       
   489   //   so that we can log the value in the referent field with an SATB
       
   490   //   update buffer.
       
   491   //   If the code for the getfield template is modified so that the
       
   492   //   G1 pre-barrier code is executed when the current method is
       
   493   //   Reference.get() then going through the normal method entry
       
   494   //   will be fine.
       
   495   // * The G1 code can, however, check the receiver object (the instance
       
   496   //   of java.lang.Reference) and jump to the slow path if null. If the
       
   497   //   Reference object is null then we obviously cannot fetch the referent
       
   498   //   and so we don't need to call the G1 pre-barrier. Thus we can use the
       
   499   //   regular method entry code to generate the NPE.
       
   500   //
       
   501 
       
   502   if (UseG1GC) {
       
   503     address entry = __ pc();
       
   504 
       
   505     const int referent_offset = java_lang_ref_Reference::referent_offset;
       
   506     guarantee(referent_offset > 0, "referent offset not initialized");
       
   507 
       
   508     Label slow_path;
       
   509 
       
   510     // Debugging not possible, so can't use __ skip_if_jvmti_mode(slow_path, GR31_SCRATCH);
       
   511 
       
   512     // In the G1 code we don't check if we need to reach a safepoint. We
       
   513     // continue and the thread will safepoint at the next bytecode dispatch.
       
   514 
       
   515     // If the receiver is null then it is OK to jump to the slow path.
       
   516     __ ld(R3_RET, Interpreter::stackElementSize, R15_esp); // get receiver
       
   517 
       
   518     // Check if receiver == NULL and go the slow path.
       
   519     __ cmpdi(CCR0, R3_RET, 0);
       
   520     __ beq(CCR0, slow_path);
       
   521 
       
   522     // Load the value of the referent field.
       
   523     __ load_heap_oop(R3_RET, referent_offset, R3_RET);
       
   524 
       
   525     // Generate the G1 pre-barrier code to log the value of
       
   526     // the referent field in an SATB buffer. Note with
       
   527     // these parameters the pre-barrier does not generate
       
   528     // the load of the previous value.
       
   529 
       
   530     // Restore caller sp for c2i case.
       
   531 #ifdef ASSERT
       
   532       __ ld(R9_ARG7, 0, R1_SP);
       
   533       __ ld(R10_ARG8, 0, R21_sender_SP);
       
   534       __ cmpd(CCR0, R9_ARG7, R10_ARG8);
       
   535       __ asm_assert_eq("backlink", 0x544);
       
   536 #endif // ASSERT
       
   537     __ mr(R1_SP, R21_sender_SP); // Cut the stack back to where the caller started.
       
   538 
       
   539     __ g1_write_barrier_pre(noreg,         // obj
       
   540                             noreg,         // offset
       
   541                             R3_RET,        // pre_val
       
   542                             R11_scratch1,  // tmp
       
   543                             R12_scratch2,  // tmp
       
   544                             true);         // needs_frame
       
   545 
       
   546     __ blr();
       
   547 
       
   548     // Generate regular method entry.
       
   549     __ bind(slow_path);
       
   550     __ jump_to_entry(Interpreter::entry_for_kind(Interpreter::zerolocals), R11_scratch1);
       
   551     return entry;
       
   552   }
       
   553 
       
   554   return NULL;
       
   555 }