[turbofan] Optimize variable loads in DYNAMIC_GLOBAL mode.

src/compiler/ast-graph-builder.h

Index: src/compiler/ast-graph-builder.h
diff --git a/src/compiler/ast-graph-builder.h b/src/compiler/ast-graph-builder.h
index f9b8b84359f998d1d1321133bc11835ba6750a3a..78cf11f640bb4e49554035c81f6ccca4c7509469 100644
--- a/src/compiler/ast-graph-builder.h
+++ b/src/compiler/ast-graph-builder.h
@@ -208,9 +208,9 @@ class AstGraphBuilder : public AstVisitor {
   void UpdateControlDependencyToLeaveFunction(Node* exit);
 
   // Builds deoptimization for a given node.
-  void PrepareFrameState(
-      Node* node, BailoutId ast_id,
-      OutputFrameStateCombine combine = OutputFrameStateCombine::Ignore());
+  void PrepareFrameState(Node* node, BailoutId ast_id,
+                         OutputFrameStateCombine framestate_combine =
+                             OutputFrameStateCombine::Ignore());
 
   BitVector* GetVariablesAssignedInLoop(IterationStatement* stmt);
 
@@ -253,17 +253,30 @@ class AstGraphBuilder : public AstVisitor {
   Node* BuildRestArgumentsArray(Variable* rest, int index);
 
   // Builders for variable load and assignment.
-  Node* BuildVariableAssignment(
-      FrameStateBeforeAndAfter& states, Variable* var, Node* value,
-      Token::Value op, BailoutId bailout_id,
-      OutputFrameStateCombine combine = OutputFrameStateCombine::Ignore());
+  Node* BuildVariableAssignment(Variable* var, Node* value, Token::Value op,
+                                BailoutId bailout_id,
+                                FrameStateBeforeAndAfter& states,
+                                OutputFrameStateCombine framestate_combine =
+                                    OutputFrameStateCombine::Ignore());
   Node* BuildVariableDelete(Variable* var, BailoutId bailout_id,
-                            OutputFrameStateCombine combine);
-  Node* BuildVariableLoad(FrameStateBeforeAndAfter& states, Variable* var,
-                          BailoutId bailout_id, const VectorSlotPair& feedback,
-                          OutputFrameStateCombine combine,
+                            OutputFrameStateCombine framestate_combine);
+  Node* BuildVariableLoad(Variable* var, BailoutId bailout_id,
+                          FrameStateBeforeAndAfter& states,
+                          const VectorSlotPair& feedback,
+                          OutputFrameStateCombine framestate_combine,
                           ContextualMode mode = CONTEXTUAL);
 
+  // Builders for variables using the global object.
+  Node* BuildGlobalVariableLoad(Variable* var, BailoutId bailout_id,
+                                FrameStateBeforeAndAfter& states,
+                                const VectorSlotPair& feedback,
+                                OutputFrameStateCombine framestate_combine,
+                                ContextualMode contextual_mode);
+
+  // Builders for variables using dynamic lookup.
+  Node* BuildDynamicVariableLoad(Variable* var, BailoutId bailout_id,
+                                 ContextualMode contextual_mode);
+
   // Builders for property loads and stores.
   Node* BuildKeyedLoad(Node* receiver, Node* key,
                        const VectorSlotPair& feedback);
@@ -320,6 +333,19 @@ class AstGraphBuilder : public AstVisitor {
   Node* ProcessArguments(const Operator* op, int arity);
 
   // ===========================================================================
+  // The following build methods have the same contract as the above ones, but
+  // they can also return {NULL} to indicate that no fragment was built. Note
+  // that these are optimizations, disabling any of them should still produce
+  // correct graphs.
+
+  // Optimizers for variable load and assignment requiring dynamic lookup.
+  Node* TryVariableLoadDynamicGlobal(Variable* variable, BailoutId bailout_id,
+                                     FrameStateBeforeAndAfter& states,
+                                     const VectorSlotPair& feedback,
+                                     OutputFrameStateCombine framestate_combine,
+                                     ContextualMode contextual_mode);
+
+  // ===========================================================================
   // The following visitation methods all recursively visit a subtree of the
   // underlying AST and extent the graph. The operand stack is mutated in a way
   // consistent with other compilers: