Optimize Crankshaft array literal initialization from boilerplate.

src/arm/lithium-codegen-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 4213 matching lines @@
   }
 
   // Check the holder map.
   __ ldr(temp2, FieldMemOperand(temp1, HeapObject::kMapOffset));
   __ cmp(temp2, Operand(Handle<Map>(current_prototype->map())));
   DeoptimizeIf(ne, instr->environment());
 }
 
 
 void LCodeGen::DoArrayLiteral(LArrayLiteral* instr) {
-  Handle<FixedArray> constant_elements = instr->hydrogen()->constant_elements();
-  ASSERT_EQ(2, constant_elements->length());
-  ElementsKind constant_elements_kind =
-      static_cast<ElementsKind>(Smi::cast(constant_elements->get(0))->value());
+  Heap* heap = isolate()->heap();
+  ElementsKind boilerplate_elements_kind =
+      instr->hydrogen()->boilerplate_elements_kind();
+
+  // Deopt if the array literal boilerplate ElementsKind is of a type different
+  // than the expected one. The check isn't necessary if the boilerplate has
+  // already been converted to FAST_ELEMENTS.
+  if (boilerplate_elements_kind != FAST_ELEMENTS) {
+    LoadHeapObject(r1, instr->hydrogen()->boilerplate_object());
+    // Load map into r2.
+    __ ldr(r2, FieldMemOperand(r1, HeapObject::kMapOffset));
+    // Load the map's "bit field 2".
+    __ ldrb(r2, FieldMemOperand(r2, Map::kBitField2Offset));
+    // Retrieve elements_kind from bit field 2.
+    __ ubfx(r2, r2, Map::kElementsKindShift, Map::kElementsKindBitCount);
+    __ cmp(r2, Operand(boilerplate_elements_kind));
+    DeoptimizeIf(ne, instr->environment());
+  }
 
   __ ldr(r3, MemOperand(fp, JavaScriptFrameConstants::kFunctionOffset));
   __ ldr(r3, FieldMemOperand(r3, JSFunction::kLiteralsOffset));
   __ mov(r2, Operand(Smi::FromInt(instr->hydrogen()->literal_index())));
-  __ mov(r1, Operand(constant_elements));
+  // Boilerplate already exists, constant elements are never accessed.
+  // Pass an empty fixed array.
+  __ mov(r1, Operand(Handle<FixedArray>(heap->empty_fixed_array())));
   __ Push(r3, r2, r1);
 
   // Pick the right runtime function or stub to call.
   int length = instr->hydrogen()->length();
   if (instr->hydrogen()->IsCopyOnWrite()) {
     ASSERT(instr->hydrogen()->depth() == 1);
     FastCloneShallowArrayStub::Mode mode =
         FastCloneShallowArrayStub::COPY_ON_WRITE_ELEMENTS;
     FastCloneShallowArrayStub stub(mode, length);
     CallCode(stub.GetCode(), RelocInfo::CODE_TARGET, instr);
   } else if (instr->hydrogen()->depth() > 1) {
     CallRuntime(Runtime::kCreateArrayLiteral, 3, instr);
   } else if (length > FastCloneShallowArrayStub::kMaximumClonedLength) {
     CallRuntime(Runtime::kCreateArrayLiteralShallow, 3, instr);
   } else {
     FastCloneShallowArrayStub::Mode mode =
-        constant_elements_kind == FAST_DOUBLE_ELEMENTS
-        ? FastCloneShallowArrayStub::CLONE_DOUBLE_ELEMENTS
-        : FastCloneShallowArrayStub::CLONE_ELEMENTS;
+        boilerplate_elements_kind == FAST_DOUBLE_ELEMENTS
+            ? FastCloneShallowArrayStub::CLONE_DOUBLE_ELEMENTS
+            : FastCloneShallowArrayStub::CLONE_ELEMENTS;
     FastCloneShallowArrayStub stub(mode, length);
     CallCode(stub.GetCode(), RelocInfo::CODE_TARGET, instr);
   }
 }
 
 
 void LCodeGen::EmitDeepCopy(Handle<JSObject> object,
                             Register result,
                             Register source,
                             int* offset) {
@@ skipping 411 matching lines @@
   ASSERT(osr_pc_offset_ == -1);
   osr_pc_offset_ = masm()->pc_offset();
 }
 
 
 
 
 #undef __
 
 } }  // namespace v8::internal