Refactor and clean up array allocation across platforms.

src/arm/builtins-arm.cc

 // Copyright 2011 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 68 matching lines @@
   __ ldr(result, MemOperand(cp, Context::SlotOffset(Context::GLOBAL_INDEX)));
   __ ldr(result,
          FieldMemOperand(result, GlobalObject::kGlobalContextOffset));
   // Load the Array function from the global context.
   __ ldr(result,
          MemOperand(result,
                     Context::SlotOffset(Context::ARRAY_FUNCTION_INDEX)));
 }
 
 
-// This constant has the same value as JSArray::kPreallocatedArrayElements and
-// if JSArray::kPreallocatedArrayElements is changed handling of loop unfolding
-// below should be reconsidered.
-static const int kLoopUnfoldLimit = 4;
-
-
 // Allocate an empty JSArray. The allocated array is put into the result
 // register. An elements backing store is allocated with size initial_capacity
 // and filled with the hole values.
 static void AllocateEmptyJSArray(MacroAssembler* masm,
                                  Register array_function,
                                  Register result,
                                  Register scratch1,
                                  Register scratch2,
                                  Register scratch3,
-                                 int initial_capacity,
                                  Label* gc_required) {
-  ASSERT(initial_capacity > 0);
+  int initial_capacity = JSArray::kPreallocatedArrayElements;

[Kevin Millikin (Chromium), 2011/10/24 08:00:38]

Drive by:

Make this a const, and make the asserts that use it into STATIC_ASSERT where
possible.

+  ASSERT(initial_capacity >= 0);
   // Load the initial map from the array function.
   __ ldr(scratch1, FieldMemOperand(array_function,
                                    JSFunction::kPrototypeOrInitialMapOffset));
 
   // Allocate the JSArray object together with space for a fixed array with the
   // requested elements.
   int size = JSArray::kSize + FixedArray::SizeFor(initial_capacity);
   __ AllocateInNewSpace(size,
                         result,
                         scratch2,
@@ skipping 31 matching lines @@
   // scratch2: start of next object
   __ LoadRoot(scratch3, Heap::kFixedArrayMapRootIndex);
   ASSERT_EQ(0 * kPointerSize, FixedArray::kMapOffset);
   __ str(scratch3, MemOperand(scratch1, kPointerSize, PostIndex));
   __ mov(scratch3,  Operand(Smi::FromInt(initial_capacity)));
   ASSERT_EQ(1 * kPointerSize, FixedArray::kLengthOffset);
   __ str(scratch3, MemOperand(scratch1, kPointerSize, PostIndex));
 
   // Fill the FixedArray with the hole value.
   ASSERT_EQ(2 * kPointerSize, FixedArray::kHeaderSize);
-  ASSERT(initial_capacity <= kLoopUnfoldLimit);
   __ LoadRoot(scratch3, Heap::kTheHoleValueRootIndex);
   for (int i = 0; i < initial_capacity; i++) {
     __ str(scratch3, MemOperand(scratch1, kPointerSize, PostIndex));
   }
 }
 
 // Allocate a JSArray with the number of elements stored in a register. The
 // register array_function holds the built-in Array function and the register
 // array_size holds the size of the array as a smi. The allocated array is put
 // into the result register and beginning and end of the FixedArray elements
 // storage is put into registers elements_array_storage and elements_array_end
 // (see  below for when that is not the case). If the parameter fill_with_holes
 // is true the allocated elements backing store is filled with the hole values
 // otherwise it is left uninitialized. When the backing store is filled the
 // register elements_array_storage is scratched.
 static void AllocateJSArray(MacroAssembler* masm,
                             Register array_function,  // Array function.
-                            Register array_size,  // As a smi.
+                            Register array_size,  // As a smi, cannot be 0.
                             Register result,
                             Register elements_array_storage,
                             Register elements_array_end,
                             Register scratch1,
                             Register scratch2,
                             bool fill_with_hole,
                             Label* gc_required) {
-  Label not_empty, allocated;
-
   // Load the initial map from the array function.
   __ ldr(elements_array_storage,
          FieldMemOperand(array_function,
                          JSFunction::kPrototypeOrInitialMapOffset));
 
-  // Check whether an empty sized array is requested.
-  __ tst(array_size, array_size);
-  __ b(ne, &not_empty);
-
-  // If an empty array is requested allocate a small elements array anyway. This
-  // keeps the code below free of special casing for the empty array.
-  int size = JSArray::kSize +
-             FixedArray::SizeFor(JSArray::kPreallocatedArrayElements);
-  __ AllocateInNewSpace(size,
-                        result,
-                        elements_array_end,
-                        scratch1,
-                        gc_required,
-                        TAG_OBJECT);
-  __ jmp(&allocated);
+  if (FLAG_debug_code) {  // Assert that array size is not zero.
+    Label not_empty;
+    __ tst(array_size, array_size);
+    __ b(ne, &not_empty);

[Kevin Millikin (Chromium), 2011/10/24 08:00:38]

Drive by:

You can replace all this with:

if (FLAG_debug_code) {
  __ tst(array_size, array_size);
  __ Assert(ne, "array size is unexpectedly 0");
}

+    __ Abort("array size is unexpectedly 0");
+    __ bind(&not_empty);
+  }
 
   // Allocate the JSArray object together with space for a FixedArray with the
   // requested number of elements.
-  __ bind(&not_empty);
   STATIC_ASSERT(kSmiTagSize == 1 && kSmiTag == 0);
   __ mov(elements_array_end,
          Operand((JSArray::kSize + FixedArray::kHeaderSize) / kPointerSize));
   __ add(elements_array_end,
          elements_array_end,
          Operand(array_size, ASR, kSmiTagSize));
   __ AllocateInNewSpace(
       elements_array_end,
       result,
       scratch1,
       scratch2,
       gc_required,
       static_cast<AllocationFlags>(TAG_OBJECT | SIZE_IN_WORDS));
 
   // Allocated the JSArray. Now initialize the fields except for the elements
   // array.
   // result: JSObject
   // elements_array_storage: initial map
   // array_size: size of array (smi)
-  __ bind(&allocated);
   __ str(elements_array_storage, FieldMemOperand(result, JSObject::kMapOffset));
   __ LoadRoot(elements_array_storage, Heap::kEmptyFixedArrayRootIndex);
   __ str(elements_array_storage,
          FieldMemOperand(result, JSArray::kPropertiesOffset));
   // Field JSArray::kElementsOffset is initialized later.
   __ str(array_size, FieldMemOperand(result, JSArray::kLengthOffset));
 
   // Calculate the location of the elements array and set elements array member
   // of the JSArray.
   // result: JSObject
   // array_size: size of array (smi)
   __ add(elements_array_storage, result, Operand(JSArray::kSize));
   __ str(elements_array_storage,
          FieldMemOperand(result, JSArray::kElementsOffset));
 
   // Clear the heap tag on the elements array.
   STATIC_ASSERT(kSmiTag == 0);
   __ sub(elements_array_storage,
          elements_array_storage,
          Operand(kHeapObjectTag));
   // Initialize the fixed array and fill it with holes. FixedArray length is
   // stored as a smi.
   // result: JSObject
   // elements_array_storage: elements array (untagged)
   // array_size: size of array (smi)
   __ LoadRoot(scratch1, Heap::kFixedArrayMapRootIndex);
   ASSERT_EQ(0 * kPointerSize, FixedArray::kMapOffset);
   __ str(scratch1, MemOperand(elements_array_storage, kPointerSize, PostIndex));
   STATIC_ASSERT(kSmiTag == 0);
-  __ tst(array_size, array_size);
-  // Length of the FixedArray is the number of pre-allocated elements if
-  // the actual JSArray has length 0 and the size of the JSArray for non-empty
-  // JSArrays. The length of a FixedArray is stored as a smi.
-  __ mov(array_size,
-         Operand(Smi::FromInt(JSArray::kPreallocatedArrayElements)),
-         LeaveCC,
-         eq);
   ASSERT_EQ(1 * kPointerSize, FixedArray::kLengthOffset);
   __ str(array_size,
          MemOperand(elements_array_storage, kPointerSize, PostIndex));
 
   // Calculate elements array and elements array end.
   // result: JSObject
   // elements_array_storage: elements array element storage
   // array_size: smi-tagged size of elements array
   STATIC_ASSERT(kSmiTag == 0 && kSmiTagSize < kPointerSizeLog2);
   __ add(elements_array_end,
@@ skipping 27 matching lines @@
 //   sp[0]: last argument
 // This function is used for both construct and normal calls of Array. The only
 // difference between handling a construct call and a normal call is that for a
 // construct call the constructor function in r1 needs to be preserved for
 // entering the generic code. In both cases argc in r0 needs to be preserved.
 // Both registers are preserved by this code so no need to differentiate between
 // construct call and normal call.
 static void ArrayNativeCode(MacroAssembler* masm,
                             Label* call_generic_code) {
   Counters* counters = masm->isolate()->counters();
-  Label argc_one_or_more, argc_two_or_more;
+  Label argc_one_or_more, argc_two_or_more, not_empty_array, empty_array;
 
   // Check for array construction with zero arguments or one.
   __ cmp(r0, Operand(0, RelocInfo::NONE));
   __ b(ne, &argc_one_or_more);
 
   // Handle construction of an empty array.
+  __ bind(&empty_array);
   AllocateEmptyJSArray(masm,
                        r1,
                        r2,
                        r3,
                        r4,
                        r5,
-                       JSArray::kPreallocatedArrayElements,
                        call_generic_code);
   __ IncrementCounter(counters->array_function_native(), 1, r3, r4);
   // Setup return value, remove receiver from stack and return.
   __ mov(r0, r2);
   __ add(sp, sp, Operand(kPointerSize));
   __ Jump(lr);
 
   // Check for one argument. Bail out if argument is not smi or if it is
   // negative.
   __ bind(&argc_one_or_more);
   __ cmp(r0, Operand(1));
   __ b(ne, &argc_two_or_more);
   STATIC_ASSERT(kSmiTag == 0);
   __ ldr(r2, MemOperand(sp));  // Get the argument from the stack.
+  __ tst(r2, r2);
+  __ b(ne, &not_empty_array);
+  __ Drop(1);  // Adjust stack.
+  __ mov(r0, Operand(0));  // Treat this as a call with argc of zero.
+  __ b(&empty_array);
+
+  __ bind(&not_empty_array);
   __ and_(r3, r2, Operand(kIntptrSignBit | kSmiTagMask), SetCC);
   __ b(ne, call_generic_code);
 
   // Handle construction of an empty array of a certain size. Bail out if size
   // is too large to actually allocate an elements array.
   STATIC_ASSERT(kSmiTag == 0);
   __ cmp(r2, Operand(JSObject::kInitialMaxFastElementArray << kSmiTagSize));
   __ b(ge, call_generic_code);
 
   // r0: argc
@@ skipping 1366 matching lines @@
   __ bind(&dont_adapt_arguments);
   __ Jump(r3);
 }
 
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_ARM