New hydrogen instruction to reduce cost of growing an array on keyed stores.

src/arm64/lithium-arm64.h

Index: src/arm64/lithium-arm64.h
diff --git a/src/arm64/lithium-arm64.h b/src/arm64/lithium-arm64.h
index 7473597b151a100cf572aa18db8b95570c69c68f..c25288ea89804febb0489a6788955ef75e28a2b3 100644
--- a/src/arm64/lithium-arm64.h
+++ b/src/arm64/lithium-arm64.h
@@ -125,6 +125,7 @@ class LCodeGen;
   V(MathRoundD)                              \
   V(MathRoundI)                              \
   V(MathSqrt)                                \
+  V(MaybeGrowElements)                       \
   V(ModByConstI)                             \
   V(ModByPowerOf2I)                          \
   V(ModI)                                    \
@@ -2637,6 +2638,28 @@ class LStoreNamedGeneric final : public LTemplateInstruction<0, 3, 0> {
 };
 
 
+class LMaybeGrowElements final : public LTemplateInstruction<1, 5, 0> {
+ public:
+  LMaybeGrowElements(LOperand* context, LOperand* object, LOperand* elements,
+                     LOperand* key, LOperand* current_capacity) {
+    inputs_[0] = context;
+    inputs_[1] = object;
+    inputs_[2] = elements;
+    inputs_[3] = key;
+    inputs_[4] = current_capacity;
+  }
+
+  LOperand* context() { return inputs_[0]; }
+  LOperand* object() { return inputs_[1]; }
+  LOperand* elements() { return inputs_[2]; }
+  LOperand* key() { return inputs_[3]; }
+  LOperand* current_capacity() { return inputs_[4]; }
+
+  DECLARE_HYDROGEN_ACCESSOR(MaybeGrowElements)
+  DECLARE_CONCRETE_INSTRUCTION(MaybeGrowElements, "maybe-grow-elements")
+};
+
+
 class LStringAdd final : public LTemplateInstruction<1, 3, 0> {
  public:
   LStringAdd(LOperand* context, LOperand* left, LOperand* right) {