[ignition] Use absolute values for jump offsets

src/interpreter/interpreter-assembler.cc

 // Copyright 2015 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/interpreter/interpreter-assembler.h"
 
 #include <limits>
 #include <ostream>
 
 #include "src/code-factory.h"
@@ skipping 377 matching lines @@
 }
 
 Node* InterpreterAssembler::BytecodeOperandUImm(int operand_index) {
   DCHECK_EQ(OperandType::kUImm,
             Bytecodes::GetOperandType(bytecode_, operand_index));
   OperandSize operand_size =
       Bytecodes::GetOperandSize(bytecode_, operand_index, operand_scale());
   return BytecodeUnsignedOperand(operand_index, operand_size);
 }
 
+Node* InterpreterAssembler::BytecodeOperandUImmWord(int operand_index) {
+  return ChangeUint32ToWord(BytecodeOperandUImm(operand_index));
+}
+
 Node* InterpreterAssembler::BytecodeOperandImm(int operand_index) {
   DCHECK_EQ(OperandType::kImm,
             Bytecodes::GetOperandType(bytecode_, operand_index));
   OperandSize operand_size =
       Bytecodes::GetOperandSize(bytecode_, operand_index, operand_scale());
   return BytecodeSignedOperand(operand_index, operand_size);
 }
 
 Node* InterpreterAssembler::BytecodeOperandImmIntPtr(int operand_index) {
   return ChangeInt32ToIntPtr(BytecodeOperandImm(operand_index));
@@ skipping 440 matching lines @@
       IntPtrAdd(function_table, ChangeUint32ToWord(function_offset));
   Node* function_entry =
       Load(MachineType::Pointer(), function,
            IntPtrConstant(offsetof(Runtime::Function, entry)));
 
   return CallStubR(callable.descriptor(), result_size, code_target, context,
                    arg_count, first_arg, function_entry);
 }
 
 void InterpreterAssembler::UpdateInterruptBudget(Node* weight) {
-  // TODO(rmcilroy): It might be worthwhile to only update the budget for
-  // backwards branches. Those are distinguishable by the {JumpLoop} bytecode.
-
   Label ok(this), interrupt_check(this, Label::kDeferred), end(this);
   Node* budget_offset =
       IntPtrConstant(BytecodeArray::kInterruptBudgetOffset - kHeapObjectTag);
 
   // Update budget by |weight| and check if it reaches zero.
   Variable new_budget(this, MachineRepresentation::kWord32);
   Node* old_budget =
       Load(MachineType::Int32(), BytecodeArrayTaggedPointer(), budget_offset);
-  new_budget.Bind(Int32Add(old_budget, weight));
+  new_budget.Bind(Int32Sub(old_budget, weight));
   Node* condition =
       Int32GreaterThanOrEqual(new_budget.value(), Int32Constant(0));
   Branch(condition, &ok, &interrupt_check);
 
   // Perform interrupt and reset budget.
   Bind(&interrupt_check);
   {
     CallRuntime(Runtime::kInterrupt, GetContext());
     new_budget.Bind(Int32Constant(Interpreter::InterruptBudget()));
     Goto(&ok);
   }
 
   // Update budget.
   Bind(&ok);
   StoreNoWriteBarrier(MachineRepresentation::kWord32,
                       BytecodeArrayTaggedPointer(), budget_offset,
                       new_budget.value());
 }
 
 Node* InterpreterAssembler::Advance() {
   return Advance(Bytecodes::Size(bytecode_, operand_scale_));
 }
 
 Node* InterpreterAssembler::Advance(int delta) {
   return Advance(IntPtrConstant(delta));
 }
 
-Node* InterpreterAssembler::Advance(Node* delta) {
+Node* InterpreterAssembler::Advance(Node* delta, bool reverse) {
   if (FLAG_trace_ignition) {
     TraceBytecode(Runtime::kInterpreterTraceBytecodeExit);
   }
-  Node* next_offset = IntPtrAdd(BytecodeOffset(), delta);
+  Node* next_offset = reverse ? IntPtrSub(BytecodeOffset(), delta)
+                              : IntPtrAdd(BytecodeOffset(), delta);
   bytecode_offset_.Bind(next_offset);
   return next_offset;
 }
 
-Node* InterpreterAssembler::Jump(Node* delta) {
+Node* InterpreterAssembler::Jump(Node* delta, bool reverse) {
   DCHECK(!Bytecodes::IsStarLookahead(bytecode_, operand_scale_));
 
-  UpdateInterruptBudget(TruncateWordToWord32(delta));
-  Node* new_bytecode_offset = Advance(delta);
+  if (reverse) {

[rmcilroy, 2017/01/17 17:58:38]

Could this be done separately (or maybe not at all depending on the impact it
has). Doing this will make our interrupt budget calculation less accurate since
we will assume we've executed any bytecodes that we actually jump over. This is
what FCG did, but it is probably better that we keep this accurate unless
updating the budget on forward jumps has a significant perf impact.

[Leszek Swirski, 2017/01/18 17:22:28]

Sure, added a "reverse" flag same as for advance. I was just doing the TODO in
UpdateInterruptBudget, should we simply get rid of that TODO?

+    UpdateInterruptBudget(TruncateWordToWord32(delta));
+  }
+  Node* new_bytecode_offset = Advance(delta, reverse);
   Node* target_bytecode = LoadBytecode(new_bytecode_offset);
   return DispatchToBytecode(target_bytecode, new_bytecode_offset);
 }
 
 void InterpreterAssembler::JumpConditional(Node* condition, Node* delta) {
   Label match(this), no_match(this);
 
   Branch(condition, &match, &no_match);
   Bind(&match);
   Jump(delta);
@@ skipping 382 matching lines @@
     Goto(&loop);
   }
   Bind(&done_loop);
 
   return array;
 }
 
 }  // namespace interpreter
 }  // namespace internal
 }  // namespace v8