[interpreter] Remove BytecodeArrayBuilder::Illegal().

src/interpreter/bytecode-peephole-optimizer.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/bytecode-peephole-optimizer.h"
 
 #include "src/interpreter/constant-array-builder.h"
 #include "src/objects-inl.h"
 #include "src/objects.h"
 
 namespace v8 {
 namespace internal {
 namespace interpreter {
 
 BytecodePeepholeOptimizer::BytecodePeepholeOptimizer(
     ConstantArrayBuilder* constant_array_builder,
     BytecodePipelineStage* next_stage)
     : constant_array_builder_(constant_array_builder),
       next_stage_(next_stage),
-      last_(Bytecode::kNop),
-      last_is_valid_(false),
       last_is_discardable_(false) {
-  // TODO(oth): Remove last_is_valid_ and use kIllegal for last_ when
-  // not invalid. Currently blocked on bytecode generator emitting
-  // kIllegal for entry not found in jump table.
+  InvalidateLast();
 }
 
-void BytecodePeepholeOptimizer::InvalidateLast() { last_is_valid_ = false; }
+void BytecodePeepholeOptimizer::InvalidateLast() {
+  last_.set_bytecode(Bytecode::kIllegal);
+}
 
-bool BytecodePeepholeOptimizer::LastIsValid() const { return last_is_valid_; }
+bool BytecodePeepholeOptimizer::LastIsValid() const {
+  return last_.bytecode() != Bytecode::kIllegal;
+}
 
 void BytecodePeepholeOptimizer::SetLast(const BytecodeNode* const node) {
   last_.Clone(node);
-  last_is_valid_ = true;
   last_is_discardable_ = true;
 }
 
 // override
 size_t BytecodePeepholeOptimizer::FlushForOffset() {
   size_t buffered_size = next_stage_->FlushForOffset();
   if (LastIsValid()) {
     if (last_.bytecode() == Bytecode::kNop &&
         !last_.source_info().is_statement()) {
       // The Nop can be dropped as it doesn't have a statement
@@ skipping 119 matching lines @@
       current->source_info().Update(last_.source_info());
     }
     InvalidateLast();
   }
   return current;
 }
 
 }  // namespace interpreter
 }  // namespace internal
 }  // namespace v8