8259316: [REDO] C1/C2 compiler support for blackholes

src/hotspot/share/c1/c1_Compiler.cpp

@@ -229,6 +229,8 @@ bool Compiler::is_intrinsic_supported(const methodHandle& method) {
     break;
   case vmIntrinsics::_getObjectSize:
     break;
+  case vmIntrinsics::_blackhole:
+    break;
   default:
     return false; // Intrinsics not on the previous list are not available.
   }

src/hotspot/share/c1/c1_GraphBuilder.cpp

@@ -3419,7 +3419,7 @@ bool GraphBuilder::try_inline(ciMethod* callee, bool holder_known, bool ignore_r
 
   // handle intrinsics
   if (callee->intrinsic_id() != vmIntrinsics::_none &&
-      (CheckIntrinsics ? callee->intrinsic_candidate() : true)) {
+      callee->check_intrinsic_candidate()) {
     if (try_inline_intrinsics(callee, ignore_return)) {
       print_inlining(callee, "intrinsic");
       if (callee->has_reserved_stack_access()) {

src/hotspot/share/c1/c1_LIRGenerator.cpp

@@ -3202,6 +3202,10 @@ void LIRGenerator::do_Intrinsic(Intrinsic* x) {
     do_vectorizedMismatch(x);
     break;
 
+  case vmIntrinsics::_blackhole:
+    do_blackhole(x);
+    break;
+
   default: ShouldNotReachHere(); break;
   }
 }
@@ -3621,6 +3625,15 @@ void LIRGenerator::do_RangeCheckPredicate(RangeCheckPredicate *x) {
   }
 }
 
+void LIRGenerator::do_blackhole(Intrinsic *x) {
+  assert(!x->has_receiver(), "Should have been checked before: only static methods here");
+  for (int c = 0; c < x->number_of_arguments(); c++) {
+    // Load the argument
+    LIRItem vitem(x->argument_at(c), this);
+    vitem.load_item();
+    // ...and leave it unused.
+  }
+}
 
 LIR_Opr LIRGenerator::call_runtime(Value arg1, address entry, ValueType* result_type, CodeEmitInfo* info) {
   LIRItemList args(1);

src/hotspot/share/c1/c1_LIRGenerator.hpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2005, 2020, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2005, 2021, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -265,6 +265,7 @@ class LIRGenerator: public InstructionVisitor, public BlockClosure {
   void do_update_CRC32(Intrinsic* x);
   void do_update_CRC32C(Intrinsic* x);
   void do_vectorizedMismatch(Intrinsic* x);
+  void do_blackhole(Intrinsic* x);
 
  public:
   LIR_Opr call_runtime(BasicTypeArray* signature, LIRItemList* args, address entry, ValueType* result_type, CodeEmitInfo* info);

src/hotspot/share/ci/ciMethod.cpp

@@ -154,6 +154,8 @@ ciMethod::ciMethod(const methodHandle& h_m, ciInstanceKlass* holder) :
     ciReplay::initialize(this);
   }
 #endif
+
+  CompilerOracle::tag_blackhole_if_possible(h_m);
 }
 
 
@@ -1214,6 +1216,7 @@ bool ciMethod::is_getter      () const {         FETCH_FLAG_FROM_VM(is_getter);
 bool ciMethod::is_setter      () const {         FETCH_FLAG_FROM_VM(is_setter); }
 bool ciMethod::is_accessor    () const {         FETCH_FLAG_FROM_VM(is_accessor); }
 bool ciMethod::is_initializer () const {         FETCH_FLAG_FROM_VM(is_initializer); }
+bool ciMethod::is_empty       () const {         FETCH_FLAG_FROM_VM(is_empty_method); }
 
 bool ciMethod::is_boxing_method() const {
   if (intrinsic_id() != vmIntrinsics::_none && holder()->is_box_klass()) {

src/hotspot/share/ci/ciMethod.hpp

@@ -204,6 +204,15 @@ class ciMethod : public ciMetadata {
   bool intrinsic_candidate()   const { return get_Method()->intrinsic_candidate();   }
   bool is_static_initializer() const { return get_Method()->is_static_initializer(); }
 
+  bool check_intrinsic_candidate() const {
+    if (intrinsic_id() == vmIntrinsics::_blackhole) {
+      // This is the intrinsic without an associated method, so no intrinsic_candidate
+      // flag is set. The intrinsic is still correct.
+      return true;
+    }
+    return (CheckIntrinsics ? intrinsic_candidate() : true);
+  }
+
   int highest_osr_comp_level();
 
   Bytecodes::Code java_code_at_bci(int bci) {
@@ -346,6 +355,7 @@ class ciMethod : public ciMetadata {
   bool is_setter      () const;
   bool is_accessor    () const;
   bool is_initializer () const;
+  bool is_empty       () const;
   bool can_be_statically_bound() const           { return _can_be_statically_bound; }
   bool has_reserved_stack_access() const         { return _has_reserved_stack_access; }
   bool is_boxing_method() const;

src/hotspot/share/classfile/classFileParser.cpp

@@ -5304,6 +5304,11 @@ static void check_methods_for_intrinsics(const InstanceKlass* ik,
           // is defined for it.
           continue;
         }
+        if (vmIntrinsics::_blackhole == id) {
+          // The _blackhole intrinsic is a special marker. No explicit method
+          // is defined for it.
+          continue;
+        }
 
         if (vmIntrinsics::class_for(id) == klass_id) {
           // Check if the current class contains a method with the same

src/hotspot/share/classfile/vmIntrinsics.cpp

@@ -153,6 +153,7 @@ bool vmIntrinsics::should_be_pinned(vmIntrinsics::ID id) {
 #endif
   case vmIntrinsics::_currentTimeMillis:
   case vmIntrinsics::_nanoTime:
+  case vmIntrinsics::_blackhole:
     return true;
   default:
     return false;

src/hotspot/share/classfile/vmIntrinsics.hpp

@@ -534,6 +534,9 @@ class methodHandle;
    do_name(     getObjectSize_name,                               "getObjectSize0")                                     \
    do_alias(    getObjectSize_signature,                          long_object_long_signature)                           \
                                                                                                                         \
+  /* special marker for blackholed methods: */                                                                          \
+  do_intrinsic(_blackhole,                java_lang_Object,       blackhole_name, star_name, F_S)                       \
+                                                                                                                        \
   /* unsafe memory references (there are a lot of them...) */                                                           \
   do_signature(getReference_signature,    "(Ljava/lang/Object;J)Ljava/lang/Object;")                                    \
   do_signature(putReference_signature,    "(Ljava/lang/Object;JLjava/lang/Object;)V")                                   \

src/hotspot/share/classfile/vmSymbols.hpp

@@ -283,6 +283,7 @@
   template(signature_name,                            "signature")                                \
   template(slot_name,                                 "slot")                                     \
   template(trusted_final_name,                        "trustedFinal")                             \
+  template(blackhole_name,                            "<blackhole>")  /*fake name*/               \
                                                                                                   \
   /* Support for annotations (JDK 1.5 and above) */                                               \
                                                                                                   \

src/hotspot/share/compiler/compilerOracle.cpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 1998, 2020, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1998, 2021, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -306,6 +306,11 @@ static void register_command(TypedMethodOptionMatcher* matcher,
   }
   assert(CompilerOracle::option_matches_type(option, value), "Value must match option type");
 
+  if (option == CompileCommand::Blackhole && !UnlockExperimentalVMOptions) {
+    warning("Blackhole compile option is experimental and must be enabled via -XX:+UnlockExperimentalVMOptions");
+    return;
+  }
+
   matcher->init(option, option_list);
   matcher->set_value<T>(value);
   option_list = matcher;
@@ -417,6 +422,37 @@ bool CompilerOracle::should_break_at(const methodHandle& method) {
   return check_predicate(CompileCommand::Break, method);
 }
 
+void CompilerOracle::tag_blackhole_if_possible(const methodHandle& method) {
+  if (!check_predicate(CompileCommand::Blackhole, method)) {
+    return;
+  }
+  guarantee(UnlockExperimentalVMOptions, "Checked during initial parsing");
+  if (method->result_type() != T_VOID) {
+    warning("Blackhole compile option only works for methods with void type: %s",
+            method->name_and_sig_as_C_string());
+    return;
+  }
+  if (!method->is_empty_method()) {
+    warning("Blackhole compile option only works for empty methods: %s",
+            method->name_and_sig_as_C_string());
+    return;
+  }
+  if (!method->is_static()) {
+    warning("Blackhole compile option only works for static methods: %s",
+            method->name_and_sig_as_C_string());
+    return;
+  }
+  if (method->intrinsic_id() == vmIntrinsics::_blackhole) {
+    return;
+  }
+  if (method->intrinsic_id() != vmIntrinsics::_none) {
+    warning("Blackhole compile option only works for methods that do not have intrinsic set: %s, %s",
+            method->name_and_sig_as_C_string(), vmIntrinsics::name_at(method->intrinsic_id()));
+    return;
+  }
+  method->set_intrinsic_id(vmIntrinsics::_blackhole);
+}
+
 static enum CompileCommand match_option_name(const char* line, int* bytes_read, char* errorbuf, int bufsize) {
   assert(ARRAY_SIZE(option_names) == static_cast<int>(CompileCommand::Count), "option_names size mismatch");
 

src/hotspot/share/compiler/compilerOracle.hpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 1998, 2019, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1998, 2021, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -51,6 +51,7 @@ class methodHandle;
   option(Print, "print", Bool) \
   option(Inline,  "inline", Bool) \
   option(DontInline,  "dontinline", Bool) \
+  option(Blackhole,  "blackhole", Bool) \
   option(CompileOnly, "compileonly", Bool)\
   option(Exclude, "exclude", Bool) \
   option(Break, "break", Bool) \
@@ -144,6 +145,9 @@ class CompilerOracle : AllStatic {
   // Tells whether there are any methods to print for print_method_statistics()
   static bool should_print_methods();
 
+  // Tags the method as blackhole candidate, if possible.
+  static void tag_blackhole_if_possible(const methodHandle& method);
+
   // A wrapper for checking bool options
   static bool has_option(const methodHandle& method, enum CompileCommand option);
 

src/hotspot/share/jvmci/jvmciEnv.cpp

@@ -28,6 +28,7 @@
 #include "classfile/symbolTable.hpp"
 #include "classfile/systemDictionary.hpp"
 #include "code/codeCache.hpp"
+#include "compiler/compilerOracle.hpp"
 #include "compiler/compileTask.hpp"
 #include "memory/oopFactory.hpp"
 #include "memory/resourceArea.hpp"
@@ -991,6 +992,7 @@ JVMCIObject JVMCIEnv::get_jvmci_method(const methodHandle& method, JVMCI_TRAPS)
   jmetadata handle = _runtime->allocate_handle(method);
   jboolean exception = false;
   if (is_hotspot()) {
+    CompilerOracle::tag_blackhole_if_possible(method);
     JavaValue result(T_OBJECT);
     JavaCallArguments args;
     args.push_long((jlong) handle);

src/hotspot/share/opto/c2compiler.cpp

@@ -677,6 +677,8 @@ bool C2Compiler::is_intrinsic_supported(const methodHandle& method, bool is_virt
   case vmIntrinsics::_VectorInsert:
   case vmIntrinsics::_VectorExtract:
     return EnableVectorSupport;
+  case vmIntrinsics::_blackhole:
+    break;
 
   default:
     return false;

src/hotspot/share/opto/classes.hpp

@@ -44,6 +44,7 @@ macro(ArrayCopy)
 macro(AryEq)
 macro(AtanD)
 macro(Binary)
+macro(Blackhole)
 macro(Bool)
 macro(BoxLock)
 macro(ReverseBytesI)

src/hotspot/share/opto/compile.cpp

@@ -3519,6 +3519,8 @@ void Compile::final_graph_reshaping_main_switch(Node* n, Final_Reshape_Counts& f
     }
     break;
   }
+  case Op_Blackhole:
+    break;
   case Op_RangeCheck: {
     RangeCheckNode* rc = n->as_RangeCheck();
     Node* iff = new IfNode(rc->in(0), rc->in(1), rc->_prob, rc->_fcnt);

src/hotspot/share/opto/library_call.cpp

@@ -111,7 +111,7 @@ JVMState* LibraryIntrinsic::generate(JVMState* jvms) {
   Node* ctrl = kit.control();
 #endif
   // Try to inline the intrinsic.
-  if ((CheckIntrinsics ? callee->intrinsic_candidate() : true) &&
+  if (callee->check_intrinsic_candidate() &&
       kit.try_to_inline(_last_predicate)) {
     const char *inline_msg = is_virtual() ? "(intrinsic, virtual)"
                                           : "(intrinsic)";
@@ -669,6 +669,9 @@ bool LibraryCallKit::try_to_inline(int predicate) {
   case vmIntrinsics::_getObjectSize:
     return inline_getObjectSize();
 
+  case vmIntrinsics::_blackhole:
+    return inline_blackhole();
+
   default:
     // If you get here, it may be that someone has added a new intrinsic
     // to the list in vmIntrinsics.hpp without implementing it here.
@@ -6911,3 +6914,23 @@ bool LibraryCallKit::inline_getObjectSize() {
 
   return true;
 }
+
+//------------------------------- inline_blackhole --------------------------------------
+//
+// Make sure all arguments to this node are alive.
+// This matches methods that were requested to be blackholed through compile commands.
+//
+bool LibraryCallKit::inline_blackhole() {
+  assert(callee()->is_static(), "Should have been checked before: only static methods here");
+  assert(callee()->is_empty(), "Should have been checked before: only empty methods here");
+  assert(callee()->holder()->is_loaded(), "Should have been checked before: only methods for loaded classes here");
+
+  // Bind call arguments as blackhole arguments to keep them alive
+  Node* bh = insert_mem_bar(Op_Blackhole);
+  uint nargs = callee()->arg_size();
+  for (uint i = 0; i < nargs; i++) {
+    bh->add_req(argument(i));
+  }
+
+  return true;
+}

src/hotspot/share/opto/library_call.hpp

@@ -344,5 +344,7 @@ class LibraryCallKit : public GraphKit {
   }
 
   bool inline_getObjectSize();
+
+  bool inline_blackhole();
 };
 

src/hotspot/share/opto/memnode.cpp

@@ -34,6 +34,7 @@
 #include "opto/addnode.hpp"
 #include "opto/arraycopynode.hpp"
 #include "opto/cfgnode.hpp"
+#include "opto/regalloc.hpp"
 #include "opto/compile.hpp"
 #include "opto/connode.hpp"
 #include "opto/convertnode.hpp"
@@ -3305,6 +3306,7 @@ MemBarNode* MemBarNode::make(Compile* C, int opcode, int atp, Node* pn) {
   case Op_OnSpinWait:        return new OnSpinWaitNode(C, atp, pn);
   case Op_Initialize:        return new InitializeNode(C, atp, pn);
   case Op_MemBarStoreStore:  return new MemBarStoreStoreNode(C, atp, pn);
+  case Op_Blackhole:         return new BlackholeNode(C, atp, pn);
   default: ShouldNotReachHere(); return NULL;
   }
 }
@@ -3539,6 +3541,27 @@ MemBarNode* MemBarNode::leading_membar() const {
   return mb;
 }
 
+#ifndef PRODUCT
+void BlackholeNode::format(PhaseRegAlloc* ra, outputStream* st) const {
+  st->print("blackhole ");
+  bool first = true;
+  for (uint i = 0; i < req(); i++) {
+    Node* n = in(i);
+    if (n != NULL && OptoReg::is_valid(ra->get_reg_first(n))) {
+      if (first) {
+        first = false;
+      } else {
+        st->print(", ");
+      }
+      char buf[128];
+      ra->dump_register(n, buf);
+      st->print("%s", buf);
+    }
+  }
+  st->cr();
+}
+#endif
+
 //===========================InitializeNode====================================
 // SUMMARY:
 // This node acts as a memory barrier on raw memory, after some raw stores.

src/hotspot/share/opto/memnode.hpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 1997, 2019, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1997, 2021, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -1337,6 +1337,26 @@ class OnSpinWaitNode: public MemBarNode {
   virtual int Opcode() const;
 };
 
+//------------------------------BlackholeNode----------------------------
+// Blackhole all arguments. This node would survive through the compiler
+// the effects on its arguments, and would be finally matched to nothing.
+class BlackholeNode : public MemBarNode {
+public:
+  BlackholeNode(Compile* C, int alias_idx, Node* precedent)
+    : MemBarNode(C, alias_idx, precedent) {}
+  virtual int   Opcode() const;
+  virtual uint ideal_reg() const { return 0; } // not matched in the AD file
+  const RegMask &in_RegMask(uint idx) const {
+    // Fake the incoming arguments mask for blackholes: accept all registers
+    // and all stack slots. This would avoid any redundant register moves
+    // for blackhole inputs.
+    return RegMask::All;
+  }
+#ifndef PRODUCT
+  virtual void format(PhaseRegAlloc* ra, outputStream* st) const;
+#endif
+};
+
 // Isolation of object setup after an AllocateNode and before next safepoint.
 // (See comment in memnode.cpp near InitializeNode::InitializeNode for semantics.)
 class InitializeNode: public MemBarNode {

src/hotspot/share/opto/node.hpp

@@ -44,6 +44,7 @@ class AllocateNode;
 class ArrayCopyNode;
 class BaseCountedLoopNode;
 class BaseCountedLoopEndNode;
+class BlackholeNode;
 class Block;
 class BoolNode;
 class BoxLockNode;