Use direct loop when filling small arrays.

src/ia32/builtins-ia32.cc

 // Copyright 2006-2009 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 788 matching lines @@
                             Register array_function,  // Array function.
                             Register array_size,  // As a smi, cannot be 0.
                             Register result,
                             Register elements_array,
                             Register elements_array_end,
                             Register scratch,
                             bool fill_with_hole,
                             Label* gc_required) {
   ASSERT(scratch.is(edi));  // rep stos destination
   ASSERT(!fill_with_hole || array_size.is(ecx));  // rep stos count
+  ASSERT(!fill_with_hole || !result.is(eax));  // result is never eax
 
   // Load the initial map from the array function.
   __ mov(elements_array,
          FieldOperand(array_function,
                       JSFunction::kPrototypeOrInitialMapOffset));
 
   // Allocate the JSArray object together with space for a FixedArray with the
   // requested elements.
   ASSERT(kSmiTagSize == 1 && kSmiTag == 0);
   __ AllocateInNewSpace(JSArray::kSize + FixedArray::kHeaderSize,
@@ skipping 37 matching lines @@
   // For non-empty JSArrays the length of the FixedArray and the JSArray is the
   // same.
   __ mov(FieldOperand(elements_array, Array::kLengthOffset), array_size);
 
   // Fill the allocated FixedArray with the hole value if requested.
   // result: JSObject
   // elements_array: elements array
   if (fill_with_hole) {
     __ lea(edi, Operand(elements_array,
                         FixedArray::kHeaderSize - kHeapObjectTag));
-
-    __ push(eax);
     __ mov(eax, Factory::the_hole_value());
-
     __ cld();
+    // Do not use rep stos when filling less than kRepStosThreshold
+    // words.
+    const int kRepStosThreshold = 16;
+    Label loop, entry, done;
+    __ cmp(ecx, kRepStosThreshold);
+    __ j(below, &loop);  // Note: ecx > 0.
     __ rep_stos();
-
-    // Restore saved registers.
-    __ pop(eax);
+    __ jmp(&done);
+    __ bind(&loop);
+    __ stos();
+    __ bind(&entry);
+    __ cmp(edi, Operand(elements_array_end));
+    __ j(below, &loop);
+    __ bind(&done);
   }
 }
 
 
 // Create a new array for the built-in Array function. This function allocates
 // the JSArray object and the FixedArray elements array and initializes these.
 // If the Array cannot be constructed in native code the runtime is called. This
 // function assumes the following state:
 //   edi: constructor (built-in Array function)
 //   eax: argc
@@ skipping 78 matching lines @@
 
   // edx: array_size (smi)
   // edi: constructor
   // esp[0]: argc (cannot be 0 here)
   // esp[4]: constructor (only if construct_call)
   // esp[8]: return address
   // esp[C]: argument
   AllocateJSArray(masm,
                   edi,
                   ecx,
+                  ebx,
                   eax,
-                  ebx,
                   edx,
                   edi,
                   true,
                   &prepare_generic_code_call);
   __ IncrementCounter(&Counters::array_function_native, 1);
+  __ mov(eax, ebx);
   __ pop(ebx);
   if (construct_call) {
     __ pop(edi);
   }
   __ ret(2 * kPointerSize);
 
   // Handle construction of an array from a list of arguments.
   __ bind(&argc_two_or_more);
   ASSERT(kSmiTag == 0);
   __ SmiTag(eax);  // Convet argc to a smi.
@@ skipping 250 matching lines @@
   // Dont adapt arguments.
   // -------------------------------------------
   __ bind(&dont_adapt_arguments);
   __ jmp(Operand(edx));
 }
 
 
 #undef __
 
 } }  // namespace v8::internal