[builtins] Simplify String constructor code.

src/arm/builtins-arm.cc

Index: src/arm/builtins-arm.cc
diff --git a/src/arm/builtins-arm.cc b/src/arm/builtins-arm.cc
index c29c65662bfa2999b202f40e84cf34ca5b21f772..b01424e996eeb90a9ade1a9770da01e491431c3f 100644
--- a/src/arm/builtins-arm.cc
+++ b/src/arm/builtins-arm.cc
@@ -144,121 +144,74 @@ void Builtins::Generate_StringConstructCode(MacroAssembler* masm) {
   //  -- sp[(argc - n - 1) * 4] : arg[n] (zero based)
   //  -- sp[argc * 4]           : receiver
   // -----------------------------------
-  Counters* counters = masm->isolate()->counters();
-  __ IncrementCounter(counters->string_ctor_calls(), 1, r2, r3);
 
-  Register function = r1;
-  if (FLAG_debug_code) {
-    __ LoadGlobalFunction(Context::STRING_FUNCTION_INDEX, r2);
-    __ cmp(function, Operand(r2));
-    __ Assert(eq, kUnexpectedStringFunction);
+  // 1. Load the first argument into r2 and get rid of the rest (including the
+  // receiver).
+  {
+    Label no_arguments, done;
+    __ cmp(r0, Operand(0));
+    __ b(eq, &no_arguments);
+    __ sub(r0, r0, Operand(1));
+    __ ldr(r2, MemOperand(sp, r0, LSL, kPointerSizeLog2, PreIndex));
+    __ Drop(2);
+    __ b(&done);
+    __ bind(&no_arguments);
+    __ LoadRoot(r2, Heap::kempty_stringRootIndex);
+    __ Drop(1);
+    __ bind(&done);
   }
 
-  // Load the first arguments in r0 and get rid of the rest.
-  Label no_arguments;
-  __ cmp(r0, Operand::Zero());
-  __ b(eq, &no_arguments);
-  // First args = sp[(argc - 1) * 4].
-  __ sub(r0, r0, Operand(1));
-  __ ldr(r0, MemOperand(sp, r0, LSL, kPointerSizeLog2, PreIndex));
-  // sp now point to args[0], drop args[0] + receiver.
-  __ Drop(2);
-
-  Register argument = r2;
-  Label not_cached, argument_is_string;
-  __ LookupNumberStringCache(r0,        // Input.
-                             argument,  // Result.
-                             r3,        // Scratch.
-                             r4,        // Scratch.
-                             r5,        // Scratch.
-                             &not_cached);
-  __ IncrementCounter(counters->string_ctor_cached_number(), 1, r3, r4);
-  __ bind(&argument_is_string);
-
-  // ----------- S t a t e -------------
-  //  -- r2     : argument converted to string
-  //  -- r1     : constructor function
-  //  -- lr     : return address
-  // -----------------------------------
-
-  Label gc_required;
-  __ Allocate(JSValue::kSize,
-              r0,  // Result.
-              r3,  // Scratch.
-              r4,  // Scratch.
-              &gc_required,
-              TAG_OBJECT);
-
-  // Initialising the String Object.
-  Register map = r3;
-  __ LoadGlobalFunctionInitialMap(function, map, r4);
-  if (FLAG_debug_code) {
-    __ ldrb(r4, FieldMemOperand(map, Map::kInstanceSizeOffset));
-    __ cmp(r4, Operand(JSValue::kSize >> kPointerSizeLog2));
-    __ Assert(eq, kUnexpectedStringWrapperInstanceSize);
-    __ ldrb(r4, FieldMemOperand(map, Map::kUnusedPropertyFieldsOffset));
-    __ cmp(r4, Operand::Zero());
-    __ Assert(eq, kUnexpectedUnusedPropertiesOfStringWrapper);
+  // 2. Make sure r2 is a string.
+  {
+    Label convert, done_convert;
+    __ JumpIfSmi(r2, &convert);
+    __ CompareObjectType(r2, r3, r3, FIRST_NONSTRING_TYPE);
+    __ b(lo, &done_convert);
+    __ bind(&convert);
+    {
+      FrameAndConstantPoolScope scope(masm, StackFrame::INTERNAL);
+      ToStringStub stub(masm->isolate());
+      __ Move(r0, r2);
+      __ CallStub(&stub);
+      __ Move(r2, r0);
+    }
+    __ LoadGlobalFunction(Context::STRING_FUNCTION_INDEX, r1);

[Jarin, 2015/09/14 07:11:40]

Maybe some comment about the incoming r1 being the same as the context's string
constructor?

[Benedikt Meurer, 2015/09/14 07:26:39]

Done.

+    __ bind(&done_convert);
   }
-  __ str(map, FieldMemOperand(r0, HeapObject::kMapOffset));
 
-  __ LoadRoot(r3, Heap::kEmptyFixedArrayRootIndex);
-  __ str(r3, FieldMemOperand(r0, JSObject::kPropertiesOffset));
-  __ str(r3, FieldMemOperand(r0, JSObject::kElementsOffset));
-
-  __ str(argument, FieldMemOperand(r0, JSValue::kValueOffset));
-
-  // Ensure the object is fully initialized.
-  STATIC_ASSERT(JSValue::kSize == 4 * kPointerSize);
+  // 3. Allocate a JSValue wrapper for the string.
+  {
+    // ----------- S t a t e -------------
+    //  -- r1 : constructor function
+    //  -- r2 : the first argument
+    //  -- lr : return address
+    // -----------------------------------
 
-  __ Ret();
+    Label allocate, done_allocate;
+    __ Allocate(JSValue::kSize, r0, r3, r4, &allocate, TAG_OBJECT);
+    __ bind(&done_allocate);
+
+    // Initialize the JSValue in eax.
+    __ LoadGlobalFunctionInitialMap(r1, r3, r4);
+    __ str(r3, FieldMemOperand(r0, HeapObject::kMapOffset));
+    __ LoadRoot(r3, Heap::kEmptyFixedArrayRootIndex);
+    __ str(r3, FieldMemOperand(r0, JSObject::kPropertiesOffset));
+    __ str(r3, FieldMemOperand(r0, JSObject::kElementsOffset));
+    __ str(r2, FieldMemOperand(r0, JSValue::kValueOffset));
+    STATIC_ASSERT(JSValue::kSize == 4 * kPointerSize);
+    __ Ret();
 
-  // The argument was not found in the number to string cache. Check
-  // if it's a string already before calling the conversion builtin.
-  Label convert_argument;
-  __ bind(&not_cached);
-  __ JumpIfSmi(r0, &convert_argument);
-
-  // Is it a String?
-  __ ldr(r2, FieldMemOperand(r0, HeapObject::kMapOffset));
-  __ ldrb(r3, FieldMemOperand(r2, Map::kInstanceTypeOffset));
-  STATIC_ASSERT(kNotStringTag != 0);
-  __ tst(r3, Operand(kIsNotStringMask));
-  __ b(ne, &convert_argument);
-  __ mov(argument, r0);
-  __ IncrementCounter(counters->string_ctor_conversions(), 1, r3, r4);
-  __ b(&argument_is_string);
-
-  // Invoke the conversion builtin and put the result into r2.
-  __ bind(&convert_argument);
-  __ push(function);  // Preserve the function.
-  __ IncrementCounter(counters->string_ctor_conversions(), 1, r3, r4);
-  {
-    FrameAndConstantPoolScope scope(masm, StackFrame::INTERNAL);
-    ToStringStub stub(masm->isolate());
-    __ CallStub(&stub);
-  }
-  __ pop(function);
-  __ mov(argument, r0);
-  __ b(&argument_is_string);
-
-  // Load the empty string into r2, remove the receiver from the
-  // stack, and jump back to the case where the argument is a string.
-  __ bind(&no_arguments);
-  __ LoadRoot(argument, Heap::kempty_stringRootIndex);
-  __ Drop(1);
-  __ b(&argument_is_string);
-
-  // At this point the argument is already a string. Call runtime to
-  // create a string wrapper.
-  __ bind(&gc_required);
-  __ IncrementCounter(counters->string_ctor_gc_required(), 1, r3, r4);
-  {
-    FrameAndConstantPoolScope scope(masm, StackFrame::INTERNAL);
-    __ push(argument);
-    __ CallRuntime(Runtime::kNewStringWrapper, 1);
+    // Fallback to the runtime to allocate in new space.
+    __ bind(&allocate);
+    {
+      FrameAndConstantPoolScope scope(masm, StackFrame::INTERNAL);
+      __ Move(r3, Smi::FromInt(JSValue::kSize));
+      __ Push(r1, r2, r3);
+      __ CallRuntime(Runtime::kAllocateInNewSpace, 1);
+      __ Pop(r1, r2);
+    }
+    __ b(&done_allocate);
   }
-  __ Ret();
 }