Copy-on-write arrays.

src/arm/codegen-arm.cc

 // Copyright 2010 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 3379 matching lines @@
 
   Register tos = frame_->GetTOSRegister();
   // Load the function of this activation.
   __ ldr(tos, frame_->Function());
   // Load the literals array of the function.
   __ ldr(tos, FieldMemOperand(tos, JSFunction::kLiteralsOffset));
   frame_->EmitPush(tos);
   frame_->EmitPush(Operand(Smi::FromInt(node->literal_index())));
   frame_->EmitPush(Operand(node->constant_elements()));
   int length = node->values()->length();
-  if (node->depth() > 1) {
+  if (node->constant_elements()->map() == Heap::fixed_cow_array_map()) {
+    FastCloneShallowArrayStub stub(
+        FastCloneShallowArrayStub::COPY_ON_WRITE_ELEMENTS, length);
+    frame_->CallStub(&stub, 3);
+  } else if (node->depth() > 1) {
     frame_->CallRuntime(Runtime::kCreateArrayLiteral, 3);
-  } else if (length > FastCloneShallowArrayStub::kMaximumLength) {
+  } else if (length > FastCloneShallowArrayStub::kMaximumClonedLength) {
     frame_->CallRuntime(Runtime::kCreateArrayLiteralShallow, 3);
   } else {
-    FastCloneShallowArrayStub stub(length);
+    FastCloneShallowArrayStub stub(
+        FastCloneShallowArrayStub::CLONE_ELEMENTS, length);
     frame_->CallStub(&stub, 3);
   }
   frame_->EmitPush(r0);  // save the result
   // r0: created object literal
 
   // Generate code to set the elements in the array that are not
   // literals.
   for (int i = 0; i < node->values()->length(); i++) {
     Expression* value = node->values()->at(i);
 
@@ skipping 1938 matching lines @@
 
   // Fetch the map and check if array is in fast case.
   // Check that object doesn't require security checks and
   // has no indexed interceptor.
   __ CompareObjectType(object, tmp1, tmp2, FIRST_JS_OBJECT_TYPE);
   deferred->Branch(lt);
   __ ldrb(tmp2, FieldMemOperand(tmp1, Map::kBitFieldOffset));
   __ tst(tmp2, Operand(KeyedLoadIC::kSlowCaseBitFieldMask));
   deferred->Branch(nz);
 
-  // Check the object's elements are in fast case.
+  // Check the object's elements are in fast case and writable.
   __ ldr(tmp1, FieldMemOperand(object, JSObject::kElementsOffset));
   __ ldr(tmp2, FieldMemOperand(tmp1, HeapObject::kMapOffset));
   __ LoadRoot(ip, Heap::kFixedArrayMapRootIndex);
   __ cmp(tmp2, ip);
   deferred->Branch(ne);
 
   // Smi-tagging is equivalent to multiplying by 2.
   STATIC_ASSERT(kSmiTag == 0);
   STATIC_ASSERT(kSmiTagSize == 1);
 
@@ skipping 1271 matching lines @@
       }
 
 #ifdef DEBUG
       Label check_inlined_codesize;
       masm_->bind(&check_inlined_codesize);
 #endif
       __ mov(scratch2, Operand(Factory::null_value()));
       __ cmp(scratch1, scratch2);
       deferred->Branch(ne);
 
-      // Get the elements array from the receiver and check that it
-      // is not a dictionary.
+      // Get the elements array from the receiver.
       __ ldr(scratch1, FieldMemOperand(receiver, JSObject::kElementsOffset));
-      if (FLAG_debug_code) {
-        __ ldr(scratch2, FieldMemOperand(scratch1, JSObject::kMapOffset));
-        __ LoadRoot(ip, Heap::kFixedArrayMapRootIndex);
-        __ cmp(scratch2, ip);
-        __ Assert(eq, "JSObject with fast elements map has slow elements");
-      }
+      __ AssertFastElements(scratch1);
 
       // Check that key is within bounds. Use unsigned comparison to handle
       // negative keys.
       __ ldr(scratch2, FieldMemOperand(scratch1, FixedArray::kLengthOffset));
       __ cmp(scratch2, key);
       deferred->Branch(ls);  // Unsigned less equal.
 
       // Load and check that the result is not the hole (key is a smi).
       __ LoadRoot(scratch2, Heap::kTheHoleValueRootIndex);
       __ add(scratch1,
@@ skipping 389 matching lines @@
   // boilerplate.
   Label slow_case;
   __ ldr(r3, MemOperand(sp, 2 * kPointerSize));
   __ ldr(r0, MemOperand(sp, 1 * kPointerSize));
   __ add(r3, r3, Operand(FixedArray::kHeaderSize - kHeapObjectTag));
   __ ldr(r3, MemOperand(r3, r0, LSL, kPointerSizeLog2 - kSmiTagSize));
   __ LoadRoot(ip, Heap::kUndefinedValueRootIndex);
   __ cmp(r3, ip);
   __ b(eq, &slow_case);
 
+  if (FLAG_debug_code) {
+    const char* message;
+    Heap::RootListIndex expected_map_index;
+    if (mode_ == CLONE_ELEMENTS) {
+      message = "Expected (writable) fixed array";
+      expected_map_index = Heap::kFixedArrayMapRootIndex;
+    } else {
+      ASSERT(mode_ == COPY_ON_WRITE_ELEMENTS);
+      message = "Expected copy-on-write fixed array";
+      expected_map_index = Heap::kFixedCOWArrayMapRootIndex;
+    }
+    __ push(r3);
+    __ ldr(r3, FieldMemOperand(r3, JSArray::kElementsOffset));
+    __ ldr(r3, FieldMemOperand(r3, HeapObject::kMapOffset));
+    __ LoadRoot(ip, expected_map_index);
+    __ cmp(r3, ip);
+    __ Assert(eq, message);
+    __ pop(r3);
+  }
+
   // Allocate both the JS array and the elements array in one big
   // allocation. This avoids multiple limit checks.
   __ AllocateInNewSpace(size,
                         r0,
                         r1,
                         r2,
                         &slow_case,
                         TAG_OBJECT);
 
   // Copy the JS array part.
   for (int i = 0; i < JSArray::kSize; i += kPointerSize) {
     if ((i != JSArray::kElementsOffset) || (length_ == 0)) {
       __ ldr(r1, FieldMemOperand(r3, i));
       __ str(r1, FieldMemOperand(r0, i));
     }
   }
 
   if (length_ > 0) {
     // Get hold of the elements array of the boilerplate and setup the
     // elements pointer in the resulting object.
     __ ldr(r3, FieldMemOperand(r3, JSArray::kElementsOffset));
     __ add(r2, r0, Operand(JSArray::kSize));
     __ str(r2, FieldMemOperand(r0, JSArray::kElementsOffset));
 
     // Copy the elements array.
     __ CopyFields(r2, r3, r1.bit(), elements_size / kPointerSize);
   }
 
+  if (mode_ == COPY_ON_WRITE_ELEMENTS) {
+    __ IncrementCounter(&Counters::cow_arrays_created_stub, 1, r2, r3);
+  }
+
   // Return and remove the on-stack parameters.
   __ add(sp, sp, Operand(3 * kPointerSize));
   __ Ret();
 
   __ bind(&slow_case);
   __ TailCallRuntime(Runtime::kCreateArrayLiteralShallow, 3, 1);
 }
 
 
 // Takes a Smi and converts to an IEEE 64 bit floating point value in two
@@ skipping 4454 matching lines @@
   __ bind(&string_add_runtime);
   __ TailCallRuntime(Runtime::kStringAdd, 2, 1);
 }
 
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_ARM