[turbofan] Optimize dynamic variable load of global constant.

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 3875 matching lines @@
     for (int depth = 0; bitset != 0; bitset >>= 1, depth++) {
       if ((bitset & 1) == 0) continue;
       Node* load = NewNode(
           javascript()->LoadContext(depth, Context::EXTENSION_INDEX, false),
           current_context());
       Node* check = NewNode(javascript()->StrictEqual(), load,
                             jsgraph()->TheHoleConstant());
       fast_block.BreakUnless(check, BranchHint::kTrue);
     }
 
-    // Fast case, because variable is not shadowed. Perform global slot load.
-    Node* fast = BuildGlobalLoad(name, feedback, typeof_mode);
-    states.AddToNode(fast, bailout_id, combine);
-    environment()->Push(fast);
+    // Fast case, because variable is not shadowed.
+    if (Node* constant = TryLoadGlobalConstant(name)) {
+      environment()->Push(constant);
+    } else {
+      // Perform global slot load.
+      Node* fast = BuildGlobalLoad(name, feedback, typeof_mode);
+      states.AddToNode(fast, bailout_id, combine);
+      environment()->Push(fast);
+    }
     slow_block.Break();
     environment()->Pop();
     fast_block.EndBlock();
 
     // Slow case, because variable potentially shadowed. Perform dynamic lookup.
     const Operator* op = javascript()->LoadDynamic(name, typeof_mode);
     Node* slow = NewNode(op, BuildLoadFeedbackVector(), current_context());
     states.AddToNode(slow, bailout_id, combine);
     environment()->Push(slow);
     slow_block.EndBlock();
@@ skipping 424 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