[builtins] Speed up TypedArrayInitialize in CodeStubAssembler

On those architectures that do support unaligned memory access
there is no need to emit heap alignment code in TypedArrayInitialize.

BUG=chromium:708545

Review-Url: https://codereview.chromium.org/2802003003
Cr-Commit-Position: refs/heads/master@{#44501}

src/builtins/builtins-typedarray-gen.cc

@@ -214,7 +214,17 @@ void TypedArrayBuiltinsAssembler::DoInitialize(Node* const holder, Node* length,
     // Allocate a FixedTypedArray and set the length, base pointer and external
     // pointer.
     CSA_ASSERT(this, IsRegularHeapObjectSize(total_size.value()));
-    Node* elements = AllocateInNewSpace(total_size.value(), kDoubleAlignment);
+
+    Node* elements;
+    int heap_alignment =
+        ElementSizeLog2Of(MachineType::PointerRepresentation());
+
+    if (UnalignedLoadSupported(MachineType::Float64(), heap_alignment) &&
+        UnalignedStoreSupported(MachineType::Float64(), heap_alignment)) {
+      elements = AllocateInNewSpace(total_size.value());
+    } else {
+      elements = AllocateInNewSpace(total_size.value(), kDoubleAlignment);
+    }
 
     StoreMapNoWriteBarrier(elements, fixed_typed_map.value());
     StoreObjectFieldNoWriteBarrier(elements, FixedArray::kLengthOffset, length);

src/compiler/code-assembler.cc

@@ -758,6 +758,17 @@ void CodeAssembler::Switch(Node* index, Label* default_label,
                                  labels, case_count);
 }
 
+bool CodeAssembler::UnalignedLoadSupported(const MachineType& machineType,
+                                           uint8_t alignment) const {
+  return raw_assembler()->machine()->UnalignedLoadSupported(machineType,
+                                                            alignment);
+}
+bool CodeAssembler::UnalignedStoreSupported(const MachineType& machineType,
+                                            uint8_t alignment) const {
+  return raw_assembler()->machine()->UnalignedStoreSupported(machineType,
+                                                             alignment);
+}
+
 // RawMachineAssembler delegate helpers:
 Isolate* CodeAssembler::isolate() const { return raw_assembler()->isolate(); }
 

src/compiler/code-assembler.h

@@ -420,6 +420,11 @@ class V8_EXPORT_PRIVATE CodeAssembler {
 
   void BreakOnNode(int node_id);
 
+  bool UnalignedLoadSupported(const MachineType& machineType,
+                              uint8_t alignment) const;
+  bool UnalignedStoreSupported(const MachineType& machineType,
+                               uint8_t alignment) const;
+
  protected:
   void RegisterCallGenerationCallbacks(
       const CodeAssemblerCallback& call_prologue,