[turbofan] Introduce an ExternalPointer type.

src/compiler/bytecode-graph-builder.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/compiler/bytecode-graph-builder.h"
 
 #include "src/ast/ast.h"
 #include "src/ast/scopes.h"
 #include "src/compilation-info.h"
 #include "src/compiler/bytecode-branch-analysis.h"
@@ skipping 1716 matching lines @@
 void BytecodeGraphBuilder::VisitJumpLoop() { BuildJump(); }
 
 void BytecodeGraphBuilder::VisitStackCheck() {
   PrepareEagerCheckpoint();
   Node* node = NewNode(javascript()->StackCheck());
   environment()->RecordAfterState(node, Environment::kAttachFrameState);
 }
 
 void BytecodeGraphBuilder::VisitReturn() {
   BuildLoopExitsForFunctionExit();
-  Node* pop_node = jsgraph()->Int32Constant(0);
+  Node* pop_node = jsgraph()->ZeroConstant();
   Node* control =
       NewNode(common()->Return(), pop_node, environment()->LookupAccumulator());
   MergeControlToLeaveFunction(control);
 }
 
 void BytecodeGraphBuilder::VisitDebugger() {
   PrepareEagerCheckpoint();
   Node* call =
       NewNode(javascript()->CallRuntime(Runtime::kHandleDebuggerStatement));
   environment()->BindAccumulator(call, Environment::kAttachFrameState);
@@ skipping 458 matching lines @@
     source_positions_->set_current_position(it->source_position());
     it->Advance();
   } else {
     DCHECK_GT(it->code_offset(), offset);
   }
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8