Unrolls array initialization loop for small arrays.

runtime/vm/intermediate_language_mips.cc

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/globals.h"  // Needed here to get TARGET_ARCH_MIPS.
 #if defined(TARGET_ARCH_MIPS)
 
 #include "vm/intermediate_language.h"
 
 #include "vm/dart_entry.h"
@@ skipping 2007 matching lines @@
   locs->set_out(0, Location::RegisterLocation(V0));
   return locs;
 }
 
 
 // Inlines array allocation for known constant values.
 static void InlineArrayAllocation(FlowGraphCompiler* compiler,
                                    intptr_t num_elements,
                                    Label* slow_path,
                                    Label* done) {
+  const int kInlineArraySize = 12;  // Same as kInlineInstanceSize.
   const Register kLengthReg = A1;
   const Register kElemTypeReg = A0;
   const intptr_t instance_size = Array::InstanceSize(num_elements);
 
   __ TryAllocateArray(kArrayCid, instance_size, slow_path,
                       V0,  // instance
                       T1,  // end address
                       T2,
                       T3);
   // V0: new object start as a tagged pointer.
   // T1: new object end address.
 
   // Store the type argument field.
   __ StoreIntoObjectNoBarrier(V0,
                               FieldAddress(V0, Array::type_arguments_offset()),
                               kElemTypeReg);
 
   // Set the length field.
   __ StoreIntoObjectNoBarrier(V0,
                               FieldAddress(V0, Array::length_offset()),
                               kLengthReg);
 
   // Initialize all array elements to raw_null.
   // V0: new object start as a tagged pointer.
   // T1: new object end address.
   // T2: iterator which initially points to the start of the variable
   // data area to be initialized.
   // T7: null.
   if (num_elements > 0) {
+    const intptr_t array_size = instance_size - sizeof(RawArray);
     __ LoadImmediate(T7, reinterpret_cast<int32_t>(Object::null()));
     __ AddImmediate(T2, V0, sizeof(RawArray) - kHeapObjectTag);
-
-    Label init_loop;
-    __ Bind(&init_loop);
-    __ sw(T7, Address(T2, 0));
-    __ addiu(T2, T2, Immediate(kWordSize));
-    __ BranchUnsignedLess(T2, T1, &init_loop);
+    if (array_size < (kInlineArraySize * kWordSize)) {
+      intptr_t current_offset = 0;
+      while (current_offset < array_size) {
+        __ sw(T7, Address(T2, current_offset));
+        current_offset += kWordSize;
+      }
+    } else {
+      Label init_loop;
+      __ Bind(&init_loop);
+      __ sw(T7, Address(T2, 0));
+      __ addiu(T2, T2, Immediate(kWordSize));
+      __ BranchUnsignedLess(T2, T1, &init_loop);
+    }
   }
   __ b(done);
 }
 
 
 void CreateArrayInstr::EmitNativeCode(FlowGraphCompiler* compiler) {
   __ TraceSimMsg("CreateArrayInstr");
   const Register kLengthReg = A1;
   const Register kElemTypeReg = A0;
   const Register kResultReg = V0;
@@ skipping 2844 matching lines @@
   compiler->GenerateCall(token_pos(), &label, stub_kind_, locs());
 #if defined(DEBUG)
   __ LoadImmediate(S4, kInvalidObjectPointer);
   __ LoadImmediate(S5, kInvalidObjectPointer);
 #endif
 }
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_MIPS