Add a fast case to Array.join when all the elements and the separator are fla...

src/ia32/full-codegen-ia32.cc

Index: src/ia32/full-codegen-ia32.cc
===================================================================
--- src/ia32/full-codegen-ia32.cc	(revision 5857)
+++ src/ia32/full-codegen-ia32.cc	(working copy)
@@ -3084,6 +3084,190 @@
 }
 
 
+void FullCodeGenerator::EmitFastAsciiArrayJoin(ZoneList<Expression*>* args) {
+  Label bailout;
+  Label done;
+
+  ASSERT(args->length() == 2);
+  // We will leave the separator on the stack until the end of the function.
+  VisitForStackValue(args->at(1));
+  // Load this to eax (= array)
+  VisitForAccumulatorValue(args->at(0));
+
+  // All aliases of the same register have disjoint lifetimes.
+  Register array = eax;
+  Register result_pos = no_reg;
+
+  Register index = edi;
+
+  Register current_string_length = ecx;  // Will be ecx when live.
+
+  Register current_string = edx;
+
+  Register scratch = ebx;
+
+  Register scratch_2 = esi;
+  Register new_padding_chars = scratch_2;
+
+  Operand separator = Operand(esp, 4 * kPointerSize);  // Already pushed.
+  Operand elements = Operand(esp, 3 * kPointerSize);
+  Operand result = Operand(esp, 2 * kPointerSize);
+  Operand padding_chars = Operand(esp, 1 * kPointerSize);
+  Operand array_length = Operand(esp, 0);
+  __ sub(Operand(esp), Immediate(4 * kPointerSize));
+
+
+  // Check that eax is a JSArray
+  __ test(array, Immediate(kSmiTagMask));
+  __ j(zero, &bailout);
+  __ CmpObjectType(array, JS_ARRAY_TYPE, scratch);
+  __ j(not_equal, &bailout);
+
+  // Check that the array has fast elements.
+  __ test_b(FieldOperand(scratch, Map::kBitField2Offset),
+            1 << Map::kHasFastElements);
+  __ j(zero, &bailout);
+
+  // If the array is empty, return the empty string.
+  __ mov(scratch, FieldOperand(array, JSArray::kLengthOffset));
+  __ sar(scratch, 1);
+  Label non_trivial;
+  __ j(not_zero, &non_trivial);
+  __ mov(result, Factory::empty_string());
+  __ jmp(&done);
+
+  __ bind(&non_trivial);
+  __ mov(array_length, scratch);
+
+  __ mov(scratch, FieldOperand(array, JSArray::kElementsOffset));
+  __ mov(elements, scratch);
+
+  // End of array's live range.
+  result_pos = array;
+  array = no_reg;
+
+
+  // Check that the separator is a flat ascii string.
+  __ mov(current_string, separator);
+  __ test(current_string, Immediate(kSmiTagMask));
+  __ j(zero, &bailout);
+  __ mov(scratch, FieldOperand(current_string, HeapObject::kMapOffset));
+  __ mov_b(scratch, FieldOperand(scratch, Map::kInstanceTypeOffset));
+  __ and_(scratch, Immediate(
+      kIsNotStringMask | kStringEncodingMask | kStringRepresentationMask));
+  __ cmp(scratch, kStringTag | kAsciiStringTag | kSeqStringTag);
+  __ j(not_equal, &bailout);
+  // If the separator is the empty string, replace it with NULL.
+  // The test for NULL is quicker than the empty string test, in a loop.
+  __ cmp(FieldOperand(current_string, SeqAsciiString::kLengthOffset),
+         Immediate(0));
+  Label separator_checked;
+  __ j(not_zero, &separator_checked);
+  __ mov(separator, Immediate(0));
+  __ bind(&separator_checked);
+
+  // Check that elements[0] is a flat ascii string, and copy it in new space.
+  __ mov(scratch, elements);
+  __ mov(current_string, FieldOperand(scratch, FixedArray::kHeaderSize));
+  __ test(current_string, Immediate(kSmiTagMask));
+  __ j(zero, &bailout);
+  __ mov(scratch, FieldOperand(current_string, HeapObject::kMapOffset));
+  __ mov_b(scratch, FieldOperand(scratch, Map::kInstanceTypeOffset));
+  __ and_(scratch, Immediate(
+      kIsNotStringMask | kStringEncodingMask | kStringRepresentationMask));
+  __ cmp(scratch, kStringTag | kAsciiStringTag | kSeqStringTag);
+  __ j(not_equal, &bailout);
+
+  // Allocate space to copy it.  Round up the size to the alignment granularity.
+  __ mov(current_string_length,
+         FieldOperand(current_string, String::kLengthOffset));
+  __ shr(current_string_length, 1);
+
+  // Live registers and stack values:
+  //   current_string_length: length of elements[0].
+
+  // New string result in new space = elements[0]
+  __ AllocateAsciiString(result_pos, current_string_length, scratch_2,
+                         index, no_reg, &bailout);
+  __ mov(result, result_pos);
+
+  // Adjust current_string_length to include padding bytes at end of string.
+  // Keep track of the number of padding bytes.
+  __ mov(new_padding_chars, current_string_length);
+  __ add(Operand(current_string_length), Immediate(kObjectAlignmentMask));
+  __ and_(Operand(current_string_length), Immediate(~kObjectAlignmentMask));
+  __ sub(new_padding_chars, Operand(current_string_length));
+  __ neg(new_padding_chars);
+  __ mov(padding_chars, new_padding_chars);
+
+  Label copy_loop_1_done;
+  Label copy_loop_1;
+  __ test(current_string_length, Operand(current_string_length));
+  __ j(zero, &copy_loop_1_done);
+  __ bind(&copy_loop_1);
+  __ sub(Operand(current_string_length), Immediate(kPointerSize));
+  __ mov(scratch, FieldOperand(current_string, current_string_length,
+                               times_1, SeqAsciiString::kHeaderSize));
+  __ mov(FieldOperand(result_pos, current_string_length,
+                      times_1, SeqAsciiString::kHeaderSize),
+         scratch);
+  __ j(not_zero, &copy_loop_1);
+  __ bind(&copy_loop_1_done);
+
+  __ mov(index, Immediate(1));
+  // Loop condition: while (index < length).
+  Label loop;
+  __ bind(&loop);
+  __ cmp(index, array_length);
+  __ j(greater_equal, &done);
+
+  // If the separator is the empty string, signalled by NULL, skip it.
+  Label separator_done;
+  __ mov(current_string, separator);
+  __ test(current_string, Operand(current_string));
+  __ j(zero, &separator_done);
+
+  // Append separator to result.  It is known to be a flat ascii string.
+  __ AppendStringToTopOfNewSpace(current_string, current_string_length,
+                                 result_pos, scratch, scratch_2, result,
+                                 padding_chars, &bailout);
+  __ bind(&separator_done);
+
+  // Add next element of array to the end of the result.
+  // Get current_string = array[index].
+  __ mov(scratch, elements);
+  __ mov(current_string, FieldOperand(scratch, index,
+                                      times_pointer_size,
+                                      FixedArray::kHeaderSize));
+  // If current != flat ascii string drop result, return undefined.
+  __ test(current_string, Immediate(kSmiTagMask));
+  __ j(zero, &bailout);
+  __ mov(scratch, FieldOperand(current_string, HeapObject::kMapOffset));
+  __ mov_b(scratch, FieldOperand(scratch, Map::kInstanceTypeOffset));
+  __ and_(scratch, Immediate(
+      kIsNotStringMask | kStringEncodingMask | kStringRepresentationMask));
+  __ cmp(scratch, kStringTag | kAsciiStringTag | kSeqStringTag);
+  __ j(not_equal, &bailout);
+
+  // Append current to the result.
+  __ AppendStringToTopOfNewSpace(current_string, current_string_length,
+                                 result_pos, scratch, scratch_2, result,
+                                 padding_chars, &bailout);
+  __ add(Operand(index), Immediate(1));
+  __ jmp(&loop);  // End while (index < length).
+
+  __ bind(&bailout);
+  __ mov(result, Factory::undefined_value());
+  __ bind(&done);
+  __ mov(eax, result);
+  // Drop temp values from the stack, and restore context register.
+  __ add(Operand(esp), Immediate(5 * kPointerSize));
+
+  __ mov(esi, Operand(ebp, StandardFrameConstants::kContextOffset));
+  context()->Plug(eax);
+}
+
+
 void FullCodeGenerator::VisitCallRuntime(CallRuntime* expr) {
   Handle<String> name = expr->name();
   if (name->length() > 0 && name->Get(0) == '_') {