[turbofan] Emit explicit checkpoint before operations.

src/compiler/ast-graph-builder.cc

 // 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.
 
 #include "src/compiler/ast-graph-builder.h"
 
 #include "src/ast/scopes.h"
 #include "src/compiler.h"
 #include "src/compiler/ast-loop-assignment-analyzer.h"
 #include "src/compiler/control-builders.h"
@@ skipping 400 matching lines @@
 
 
 // Helper for generating before and after frame states.
 class AstGraphBuilder::FrameStateBeforeAndAfter {
  public:
   FrameStateBeforeAndAfter(AstGraphBuilder* builder, BailoutId id_before)
       : builder_(builder), frame_state_before_(nullptr) {
     frame_state_before_ = id_before == BailoutId::None()
                               ? builder_->GetEmptyFrameState()
                               : builder_->environment()->Checkpoint(id_before);
+    // Create an explicit checkpoint node for before the operation.
+    Node* node = builder_->NewNode(builder_->common()->Checkpoint());
+    DCHECK_EQ(IrOpcode::kDead,
+              NodeProperties::GetFrameStateInput(node, 0)->opcode());
+    NodeProperties::ReplaceFrameStateInput(node, 0, frame_state_before_);
   }
 
   void AddToNode(
       Node* node, BailoutId id_after,
       OutputFrameStateCombine combine = OutputFrameStateCombine::Ignore()) {
     int count = OperatorProperties::GetFrameStateInputCount(node->op());
     DCHECK_LE(count, 2);
 
     if (count >= 1) {
       // Add the frame state for after the operation.
       DCHECK_EQ(IrOpcode::kDead,
                 NodeProperties::GetFrameStateInput(node, 0)->opcode());
 
       bool node_has_exception = NodeProperties::IsExceptionalCall(node);
 
       Node* frame_state_after =
           id_after == BailoutId::None()
               ? builder_->GetEmptyFrameState()
               : builder_->environment()->Checkpoint(id_after, combine,
                                                     node_has_exception);
 
       NodeProperties::ReplaceFrameStateInput(node, 0, frame_state_after);
     }
 
     if (count >= 2) {
       // Add the frame state for before the operation.
+      // TODO(mstarzinger): Get rid of frame state input before!
       DCHECK_EQ(IrOpcode::kDead,
                 NodeProperties::GetFrameStateInput(node, 1)->opcode());
       NodeProperties::ReplaceFrameStateInput(node, 1, frame_state_before_);
     }
   }
 
  private:
   AstGraphBuilder* builder_;
   Node* frame_state_before_;
 };
@@ skipping 3913 matching lines @@
     // Phi does not exist yet, introduce one.
     value = NewPhi(inputs, value, control);
     value->ReplaceInput(inputs - 1, other);
   }
   return value;
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8