[turbofan] Add support for accessing Uint8ClampedArrays.

src/compiler/js-native-context-specialization.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/js-native-context-specialization.h"
 
 #include "src/accessors.h"
 #include "src/code-factory.h"
 #include "src/compilation-dependencies.h"
 #include "src/compiler/access-builder.h"
@@ skipping 1182 matching lines @@
         value = effect = graph()->NewNode(
             simplified()->LoadTypedElement(external_array_type), buffer,
             base_pointer, external_pointer, index, effect, control);
         break;
       }
       case AccessMode::kStore: {
         // Ensure that the {value} is actually a Number.
         value = effect = graph()->NewNode(simplified()->CheckNumber(), value,
                                           effect, control);
 
+        // Introduce the appropriate truncation for {value}. Currently we
+        // only need to do this for ClamedUint8Array {receiver}s, as the
+        // other truncations are implicit in the StoreTypedElement, but we
+        // might want to change that at some point.
+        if (external_array_type == kExternalUint8ClampedArray) {
+          value = graph()->NewNode(simplified()->NumberToUint8Clamped(), value);
+        }
+
         // Check if we can skip the out-of-bounds store.
         if (store_mode == STORE_NO_TRANSITION_IGNORE_OUT_OF_BOUNDS) {
           Node* check =
               graph()->NewNode(simplified()->NumberLessThan(), index, length);
           Node* branch = graph()->NewNode(common()->Branch(BranchHint::kTrue),
                                           check, control);
 
           Node* if_true = graph()->NewNode(common()->IfTrue(), branch);
           Node* etrue = effect;
           {
@@ skipping 396 matching lines @@
   return jsgraph()->javascript();
 }
 
 SimplifiedOperatorBuilder* JSNativeContextSpecialization::simplified() const {
   return jsgraph()->simplified();
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8