VM: Optimized context allocation on all platforms.

runtime/vm/assembler_arm64.cc

Index: runtime/vm/assembler_arm64.cc
===================================================================
--- runtime/vm/assembler_arm64.cc	(revision 38897)
+++ runtime/vm/assembler_arm64.cc	(working copy)
@@ -1413,6 +1413,49 @@
 }
 
 
+void Assembler::TryAllocateArray(intptr_t cid,
+                                 intptr_t instance_size,
+                                 Label* failure,
+                                 Register instance,
+                                 Register end_address,
+                                 Register temp1,
+                                 Register temp2) {
+  if (FLAG_inline_alloc) {
+    Isolate* isolate = Isolate::Current();
+    Heap* heap = isolate->heap();
+    LoadImmediate(temp1, heap->TopAddress(), PP);
+    ldr(instance, Address(temp1, 0));  // Potential new object start.
+    AddImmediate(end_address, instance, instance_size, PP);
+    b(failure, VS);
+
+    // Check if the allocation fits into the remaining space.
+    // instance: potential new object start.
+    // end_address: potential next object start.
+    LoadImmediate(temp2, heap->EndAddress(), PP);
+    ldr(temp2, Address(temp2, 0));
+    cmp(end_address, Operand(temp2));
+    b(failure, CS);
+
+    // Successfully allocated the object(s), now update top to point to
+    // next object start and initialize the object.
+    str(end_address, Address(temp1, 0));
+    add(instance, instance, Operand(kHeapObjectTag));
+    LoadImmediate(temp2, instance_size, PP);
+    UpdateAllocationStatsWithSize(cid, temp2, PP);
+
+    // Initialize the tags.
+    // instance: new object start as a tagged pointer.
+    uword tags = 0;
+    tags = RawObject::ClassIdTag::update(cid, tags);
+    tags = RawObject::SizeTag::update(instance_size, tags);
+    LoadImmediate(temp2, tags, PP);
+    str(temp2, FieldAddress(instance, Array::tags_offset()));  // Store tags.
+  } else {
+    b(failure);
+  }
+}
+
+
 Address Assembler::ElementAddressForIntIndex(bool is_external,
                                              intptr_t cid,
                                              intptr_t index_scale,