Revert of [fullcodegen] Remove the hacky %_FastOneByteArrayJoin intrinsic.

src/full-codegen/arm64/full-codegen-arm64.cc

Index: src/full-codegen/arm64/full-codegen-arm64.cc
diff --git a/src/full-codegen/arm64/full-codegen-arm64.cc b/src/full-codegen/arm64/full-codegen-arm64.cc
index 87624af18c90ed68963aba50cbe7c1bff1446eb6..7f3a970c12010b90c761c806287c6e3930e72fa0 100644
--- a/src/full-codegen/arm64/full-codegen-arm64.cc
+++ b/src/full-codegen/arm64/full-codegen-arm64.cc
@@ -3240,6 +3240,226 @@
   __ Ldr(x0, FieldMemOperand(x0, HeapObject::kMapOffset));
   __ Ldr(x0, FieldMemOperand(x0, Map::kPrototypeOffset));
   context()->Plug(x0);
+}
+
+
+void FullCodeGenerator::EmitFastOneByteArrayJoin(CallRuntime* expr) {
+  ASM_LOCATION("FullCodeGenerator::EmitFastOneByteArrayJoin");
+
+  ZoneList<Expression*>* args = expr->arguments();
+  DCHECK(args->length() == 2);
+  VisitForStackValue(args->at(1));
+  VisitForAccumulatorValue(args->at(0));
+
+  Register array = x0;
+  Register result = x0;
+  Register elements = x1;
+  Register element = x2;
+  Register separator = x3;
+  Register array_length = x4;
+  Register result_pos = x5;
+  Register map = x6;
+  Register string_length = x10;
+  Register elements_end = x11;
+  Register string = x12;
+  Register scratch1 = x13;
+  Register scratch2 = x14;
+  Register scratch3 = x7;
+  Register separator_length = x15;
+
+  Label bailout, done, one_char_separator, long_separator,
+      non_trivial_array, not_size_one_array, loop,
+      empty_separator_loop, one_char_separator_loop,
+      one_char_separator_loop_entry, long_separator_loop;
+
+  // The separator operand is on the stack.
+  __ Pop(separator);
+
+  // Check that the array is a JSArray.
+  __ JumpIfSmi(array, &bailout);
+  __ JumpIfNotObjectType(array, map, scratch1, JS_ARRAY_TYPE, &bailout);
+
+  // Check that the array has fast elements.
+  __ CheckFastElements(map, scratch1, &bailout);
+
+  // If the array has length zero, return the empty string.
+  // Load and untag the length of the array.
+  // It is an unsigned value, so we can skip sign extension.
+  // We assume little endianness.
+  __ Ldrsw(array_length,
+           UntagSmiFieldMemOperand(array, JSArray::kLengthOffset));
+  __ Cbnz(array_length, &non_trivial_array);
+  __ LoadRoot(result, Heap::kempty_stringRootIndex);
+  __ B(&done);
+
+  __ Bind(&non_trivial_array);
+  // Get the FixedArray containing array's elements.
+  __ Ldr(elements, FieldMemOperand(array, JSArray::kElementsOffset));
+
+  // Check that all array elements are sequential one-byte strings, and
+  // accumulate the sum of their lengths.
+  __ Mov(string_length, 0);
+  __ Add(element, elements, FixedArray::kHeaderSize - kHeapObjectTag);
+  __ Add(elements_end, element, Operand(array_length, LSL, kPointerSizeLog2));
+  // Loop condition: while (element < elements_end).
+  // Live values in registers:
+  //   elements: Fixed array of strings.
+  //   array_length: Length of the fixed array of strings (not smi)
+  //   separator: Separator string
+  //   string_length: Accumulated sum of string lengths (not smi).
+  //   element: Current array element.
+  //   elements_end: Array end.
+  if (FLAG_debug_code) {
+    __ Cmp(array_length, 0);
+    __ Assert(gt, kNoEmptyArraysHereInEmitFastOneByteArrayJoin);
+  }
+  __ Bind(&loop);
+  __ Ldr(string, MemOperand(element, kPointerSize, PostIndex));
+  __ JumpIfSmi(string, &bailout);
+  __ Ldr(scratch1, FieldMemOperand(string, HeapObject::kMapOffset));
+  __ Ldrb(scratch1, FieldMemOperand(scratch1, Map::kInstanceTypeOffset));
+  __ JumpIfInstanceTypeIsNotSequentialOneByte(scratch1, scratch2, &bailout);
+  __ Ldrsw(scratch1,
+           UntagSmiFieldMemOperand(string, SeqOneByteString::kLengthOffset));
+  __ Adds(string_length, string_length, scratch1);
+  __ B(vs, &bailout);
+  __ Cmp(element, elements_end);
+  __ B(lt, &loop);
+
+  // If array_length is 1, return elements[0], a string.
+  __ Cmp(array_length, 1);
+  __ B(ne, &not_size_one_array);
+  __ Ldr(result, FieldMemOperand(elements, FixedArray::kHeaderSize));
+  __ B(&done);
+
+  __ Bind(&not_size_one_array);
+
+  // Live values in registers:
+  //   separator: Separator string
+  //   array_length: Length of the array (not smi).
+  //   string_length: Sum of string lengths (not smi).
+  //   elements: FixedArray of strings.
+
+  // Check that the separator is a flat one-byte string.
+  __ JumpIfSmi(separator, &bailout);
+  __ Ldr(scratch1, FieldMemOperand(separator, HeapObject::kMapOffset));
+  __ Ldrb(scratch1, FieldMemOperand(scratch1, Map::kInstanceTypeOffset));
+  __ JumpIfInstanceTypeIsNotSequentialOneByte(scratch1, scratch2, &bailout);
+
+  // Add (separator length times array_length) - separator length to the
+  // string_length to get the length of the result string.
+  // Load the separator length as untagged.
+  // We assume little endianness, and that the length is positive.
+  __ Ldrsw(separator_length,
+           UntagSmiFieldMemOperand(separator,
+                                   SeqOneByteString::kLengthOffset));
+  __ Sub(string_length, string_length, separator_length);
+  __ Umaddl(string_length, array_length.W(), separator_length.W(),
+            string_length);
+
+  // Bailout for large object allocations.
+  __ Cmp(string_length, Page::kMaxRegularHeapObjectSize);
+  __ B(gt, &bailout);
+
+  // Get first element in the array.
+  __ Add(element, elements, FixedArray::kHeaderSize - kHeapObjectTag);
+  // Live values in registers:
+  //   element: First array element
+  //   separator: Separator string
+  //   string_length: Length of result string (not smi)
+  //   array_length: Length of the array (not smi).
+  __ AllocateOneByteString(result, string_length, scratch1, scratch2, scratch3,
+                           &bailout);
+
+  // Prepare for looping. Set up elements_end to end of the array. Set
+  // result_pos to the position of the result where to write the first
+  // character.
+  // TODO(all): useless unless AllocateOneByteString trashes the register.
+  __ Add(elements_end, element, Operand(array_length, LSL, kPointerSizeLog2));
+  __ Add(result_pos, result, SeqOneByteString::kHeaderSize - kHeapObjectTag);
+
+  // Check the length of the separator.
+  __ Cmp(separator_length, 1);
+  __ B(eq, &one_char_separator);
+  __ B(gt, &long_separator);
+
+  // Empty separator case
+  __ Bind(&empty_separator_loop);
+  // Live values in registers:
+  //   result_pos: the position to which we are currently copying characters.
+  //   element: Current array element.
+  //   elements_end: Array end.
+
+  // Copy next array element to the result.
+  __ Ldr(string, MemOperand(element, kPointerSize, PostIndex));
+  __ Ldrsw(string_length,
+           UntagSmiFieldMemOperand(string, String::kLengthOffset));
+  __ Add(string, string, SeqOneByteString::kHeaderSize - kHeapObjectTag);
+  __ CopyBytes(result_pos, string, string_length, scratch1);
+  __ Cmp(element, elements_end);
+  __ B(lt, &empty_separator_loop);  // End while (element < elements_end).
+  __ B(&done);
+
+  // One-character separator case
+  __ Bind(&one_char_separator);
+  // Replace separator with its one-byte character value.
+  __ Ldrb(separator, FieldMemOperand(separator, SeqOneByteString::kHeaderSize));
+  // Jump into the loop after the code that copies the separator, so the first
+  // element is not preceded by a separator
+  __ B(&one_char_separator_loop_entry);
+
+  __ Bind(&one_char_separator_loop);
+  // Live values in registers:
+  //   result_pos: the position to which we are currently copying characters.
+  //   element: Current array element.
+  //   elements_end: Array end.
+  //   separator: Single separator one-byte char (in lower byte).
+
+  // Copy the separator character to the result.
+  __ Strb(separator, MemOperand(result_pos, 1, PostIndex));
+
+  // Copy next array element to the result.
+  __ Bind(&one_char_separator_loop_entry);
+  __ Ldr(string, MemOperand(element, kPointerSize, PostIndex));
+  __ Ldrsw(string_length,
+           UntagSmiFieldMemOperand(string, String::kLengthOffset));
+  __ Add(string, string, SeqOneByteString::kHeaderSize - kHeapObjectTag);
+  __ CopyBytes(result_pos, string, string_length, scratch1);
+  __ Cmp(element, elements_end);
+  __ B(lt, &one_char_separator_loop);  // End while (element < elements_end).
+  __ B(&done);
+
+  // Long separator case (separator is more than one character). Entry is at the
+  // label long_separator below.
+  __ Bind(&long_separator_loop);
+  // Live values in registers:
+  //   result_pos: the position to which we are currently copying characters.
+  //   element: Current array element.
+  //   elements_end: Array end.
+  //   separator: Separator string.
+
+  // Copy the separator to the result.
+  // TODO(all): hoist next two instructions.
+  __ Ldrsw(string_length,
+           UntagSmiFieldMemOperand(separator, String::kLengthOffset));
+  __ Add(string, separator, SeqOneByteString::kHeaderSize - kHeapObjectTag);
+  __ CopyBytes(result_pos, string, string_length, scratch1);
+
+  __ Bind(&long_separator);
+  __ Ldr(string, MemOperand(element, kPointerSize, PostIndex));
+  __ Ldrsw(string_length,
+           UntagSmiFieldMemOperand(string, String::kLengthOffset));
+  __ Add(string, string, SeqOneByteString::kHeaderSize - kHeapObjectTag);
+  __ CopyBytes(result_pos, string, string_length, scratch1);
+  __ Cmp(element, elements_end);
+  __ B(lt, &long_separator_loop);  // End while (element < elements_end).
+  __ B(&done);
+
+  __ Bind(&bailout);
+  // Returning undefined will force slower code to handle it.
+  __ LoadRoot(result, Heap::kUndefinedValueRootIndex);
+  __ Bind(&done);
+  context()->Plug(result);
 }