ARM64: Optimize AllocateHeapNumber to use STP.

src/arm64/code-stubs-arm64.cc

Index: src/arm64/code-stubs-arm64.cc
diff --git a/src/arm64/code-stubs-arm64.cc b/src/arm64/code-stubs-arm64.cc
index 7e8267be885ba0c9706577ce7b9ab5f4c3027165..d1122717441f8cbd45c0fcb5cde0cb8a8d3d94ad 100644
--- a/src/arm64/code-stubs-arm64.cc
+++ b/src/arm64/code-stubs-arm64.cc
@@ -1393,9 +1393,8 @@ void MathPowStub::Generate(MacroAssembler* masm) {
 
     // Return.
     __ Bind(&done);
-    __ AllocateHeapNumber(result_tagged, &call_runtime, scratch0, scratch1);
-    __ Str(result_double,
-        FieldMemOperand(result_tagged, HeapNumber::kValueOffset));
+    __ AllocateHeapNumber(result_tagged, &call_runtime, scratch0, scratch1,
+                          result_double);
     ASSERT(result_tagged.is(x0));
     __ IncrementCounter(
         masm->isolate()->counters()->math_pow(), 1, scratch0, scratch1);