[turbofan] Add comments to CodeAssembler

src/compiler/instruction-selector-impl.h

 // Copyright 2014 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.
 
 #ifndef V8_COMPILER_INSTRUCTION_SELECTOR_IMPL_H_
 #define V8_COMPILER_INSTRUCTION_SELECTOR_IMPL_H_
 
 #include "src/compiler/instruction.h"
 #include "src/compiler/instruction-selector.h"
 #include "src/compiler/linkage.h"
@@ skipping 201 matching lines @@
         return Constant(OpParameter<int64_t>(node));
       case IrOpcode::kFloat32Constant:
         return Constant(OpParameter<float>(node));
       case IrOpcode::kRelocatableInt32Constant:
       case IrOpcode::kRelocatableInt64Constant:
         return Constant(OpParameter<RelocatablePtrConstantInfo>(node));
       case IrOpcode::kFloat64Constant:
       case IrOpcode::kNumberConstant:
         return Constant(OpParameter<double>(node));
       case IrOpcode::kExternalConstant:
+      case IrOpcode::kComment:
         return Constant(OpParameter<ExternalReference>(node));
       case IrOpcode::kHeapConstant:
         return Constant(OpParameter<Handle<HeapObject>>(node));
       default:
         break;
     }
     UNREACHABLE();
     return Constant(static_cast<int32_t>(0));
   }
 
@@ skipping 151 matching lines @@
                                  // or mode_ == kFlags_set.
   BasicBlock* true_block_;       // Only valid if mode_ == kFlags_branch.
   BasicBlock* false_block_;      // Only valid if mode_ == kFlags_branch.
 };
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_COMPILER_INSTRUCTION_SELECTOR_IMPL_H_