[stubs] Port SubStringStub to TurboFan

src/code-stub-assembler.cc

Index: src/code-stub-assembler.cc
diff --git a/src/code-stub-assembler.cc b/src/code-stub-assembler.cc
index c01fb67e0947b855418701b3eace870ca7bb20a4..f87f55a479bdc9e3991f5dc48e26fc982b068168 100644
--- a/src/code-stub-assembler.cc
+++ b/src/code-stub-assembler.cc
@@ -337,10 +337,18 @@ Node* CodeStubAssembler::SmiSubWithOverflow(Node* a, Node* b) {
 
 Node* CodeStubAssembler::SmiEqual(Node* a, Node* b) { return WordEqual(a, b); }
 
+Node* CodeStubAssembler::SmiAbove(Node* a, Node* b) {
+  return UintPtrGreaterThan(a, b);
+}
+
 Node* CodeStubAssembler::SmiAboveOrEqual(Node* a, Node* b) {
   return UintPtrGreaterThanOrEqual(a, b);
 }
 
+Node* CodeStubAssembler::SmiBelow(Node* a, Node* b) {
+  return UintPtrLessThan(a, b);
+}
+
 Node* CodeStubAssembler::SmiLessThan(Node* a, Node* b) {
   return IntPtrLessThan(a, b);
 }
@@ -1301,11 +1309,44 @@ Node* CodeStubAssembler::AllocateSeqTwoByteString(Node* context, Node* length) {
   return var_result.value();
 }
 
+Node* CodeStubAssembler::AllocateSlicedOneByteString(Node* length, Node* parent,
+                                                     Node* offset) {
+  Node* result = Allocate(SlicedString::kSize);
+  Node* map = LoadRoot(Heap::kSlicedOneByteStringMapRootIndex);
+  StoreMapNoWriteBarrier(result, map);
+  StoreObjectFieldNoWriteBarrier(result, SlicedString::kLengthOffset, length,
+                                 MachineRepresentation::kTagged);
+  StoreObjectFieldNoWriteBarrier(result, SlicedString::kHashFieldOffset,
+                                 Int32Constant(String::kEmptyHashField),
+                                 MachineRepresentation::kWord32);
+  StoreObjectFieldNoWriteBarrier(result, SlicedString::kParentOffset, parent,
+                                 MachineRepresentation::kTagged);
+  StoreObjectFieldNoWriteBarrier(result, SlicedString::kOffsetOffset, offset,
+                                 MachineRepresentation::kTagged);
+  return result;
+}
+
+Node* CodeStubAssembler::AllocateSlicedTwoByteString(Node* length, Node* parent,
+                                                     Node* offset) {
+  Node* result = Allocate(SlicedString::kSize);
+  Node* map = LoadRoot(Heap::kSlicedStringMapRootIndex);
+  StoreMapNoWriteBarrier(result, map);
+  StoreObjectFieldNoWriteBarrier(result, SlicedString::kLengthOffset, length,
+                                 MachineRepresentation::kTagged);
+  StoreObjectFieldNoWriteBarrier(result, SlicedString::kHashFieldOffset,
+                                 Int32Constant(String::kEmptyHashField),
+                                 MachineRepresentation::kWord32);
+  StoreObjectFieldNoWriteBarrier(result, SlicedString::kParentOffset, parent,
+                                 MachineRepresentation::kTagged);
+  StoreObjectFieldNoWriteBarrier(result, SlicedString::kOffsetOffset, offset,
+                                 MachineRepresentation::kTagged);
+  return result;
+}
+
 Node* CodeStubAssembler::AllocateUninitializedJSArrayWithoutElements(
     ElementsKind kind, Node* array_map, Node* length, Node* allocation_site) {
   Comment("begin allocation of JSArray without elements");
   int base_size = JSArray::kSize;
-
   if (allocation_site != nullptr) {
     base_size += AllocationMemento::kSize;
   }
@@ -1638,6 +1679,75 @@ void CodeStubAssembler::CopyFixedArrayElements(
   Comment("] CopyFixedArrayElements");
 }
 
+void CodeStubAssembler::CopyStringCharacters(compiler::Node* from_string,
+                                             compiler::Node* to_string,
+                                             compiler::Node* from_index,
+                                             compiler::Node* character_count,
+                                             String::Encoding encoding) {
+  Label out(this);
+
+  // Nothing to do for zero characters.
+
+  GotoIf(SmiLessThanOrEqual(character_count, SmiConstant(Smi::FromInt(0))),
+         &out);
+
+  // Calculate offsets into the strings.
+
+  Node* from_offset;
+  Node* limit_offset;
+  Node* to_offset;
+
+  {
+    Node* byte_count = SmiUntag(character_count);
+    Node* from_byte_index = SmiUntag(from_index);
+    if (encoding == String::ONE_BYTE_ENCODING) {
+      const int offset = SeqOneByteString::kHeaderSize - kHeapObjectTag;
+      from_offset = IntPtrAdd(IntPtrConstant(offset), from_byte_index);
+      limit_offset = IntPtrAdd(from_offset, byte_count);
+      to_offset = IntPtrConstant(offset);
+    } else {
+      STATIC_ASSERT(2 == sizeof(uc16));
+      byte_count = WordShl(byte_count, 1);
+      from_byte_index = WordShl(from_byte_index, 1);
+
+      const int offset = SeqTwoByteString::kHeaderSize - kHeapObjectTag;
+      from_offset = IntPtrAdd(IntPtrConstant(offset), from_byte_index);
+      limit_offset = IntPtrAdd(from_offset, byte_count);
+      to_offset = IntPtrConstant(offset);
+    }
+  }
+
+  Variable var_from_offset(this, MachineType::PointerRepresentation());
+  Variable var_to_offset(this, MachineType::PointerRepresentation());
+
+  var_from_offset.Bind(from_offset);
+  var_to_offset.Bind(to_offset);
+
+  Variable* vars[] = {&var_from_offset, &var_to_offset};
+  Label decrement(this, 2, vars);
+
+  Label loop(this, 2, vars);
+  Goto(&loop);
+  Bind(&loop);
+  {
+    from_offset = var_from_offset.value();
+    to_offset = var_to_offset.value();
+
+    // TODO(jgruber): We could make this faster through larger copy unit sizes.
+    Node* value = Load(MachineType::Uint8(), from_string, from_offset);
+    StoreNoWriteBarrier(MachineRepresentation::kWord8, to_string, to_offset,
+                        value);
+
+    Node* new_from_offset = IntPtrAdd(from_offset, IntPtrConstant(1));
+    var_from_offset.Bind(new_from_offset);
+    var_to_offset.Bind(IntPtrAdd(to_offset, IntPtrConstant(1)));
+
+    Branch(WordNotEqual(new_from_offset, limit_offset), &loop, &out);
+  }
+
+  Bind(&out);
+}
+
 Node* CodeStubAssembler::LoadElementAndPrepareForStore(Node* array,
                                                        Node* offset,
                                                        ElementsKind from_kind,
@@ -2348,6 +2458,282 @@ Node* CodeStubAssembler::StringFromCharCode(Node* code) {
   return var_result.value();
 }
 
+namespace {
+
+// A wrapper around CopyStringCharacters which determines the correct string
+// encoding, allocates a corresponding sequential string, and then copies the
+// given character range using CopyStringCharacters.
+// |from_string| must be a sequential string. |from_index| and
+// |character_count| must be Smis s.t.
+// 0 <= |from_index| <= |from_index| + |character_count| < from_string.length.
+Node* AllocAndCopyStringCharacters(CodeStubAssembler* a, Node* context,
+                                   Node* from, Node* from_instance_type,
+                                   Node* from_index, Node* character_count) {
+  typedef CodeStubAssembler::Label Label;
+  typedef CodeStubAssembler::Variable Variable;
+
+  Label end(a), two_byte_sequential(a);
+  Variable var_result(a, MachineRepresentation::kTagged);
+
+  STATIC_ASSERT((kOneByteStringTag & kStringEncodingMask) != 0);
+  a->GotoIf(a->Word32Equal(a->Word32And(from_instance_type,
+                                        a->Int32Constant(kStringEncodingMask)),
+                           a->Int32Constant(0)),
+            &two_byte_sequential);
+
+  // The subject string is a sequential one-byte string.
+  {
+    Node* result =
+        a->AllocateSeqOneByteString(context, a->SmiToWord(character_count));
+    a->CopyStringCharacters(from, result, from_index, character_count,
+                            String::ONE_BYTE_ENCODING);
+    var_result.Bind(result);
+
+    a->Goto(&end);
+  }
+
+  // The subject string is a sequential two-byte string.
+  a->Bind(&two_byte_sequential);
+  {
+    Node* result =
+        a->AllocateSeqTwoByteString(context, a->SmiToWord(character_count));
+    a->CopyStringCharacters(from, result, from_index, character_count,
+                            String::TWO_BYTE_ENCODING);
+    var_result.Bind(result);
+
+    a->Goto(&end);
+  }
+
+  a->Bind(&end);
+  return var_result.value();
+}
+
+}  // namespace
+
+Node* CodeStubAssembler::SubString(Node* context, Node* string, Node* from,
+                                   Node* to) {
+  Label end(this);
+  Label runtime(this);
+
+  Variable var_instance_type(this, MachineRepresentation::kWord8);  // Int32.
+  Variable var_result(this, MachineRepresentation::kTagged);        // String.
+  Variable var_from(this, MachineRepresentation::kTagged);          // Smi.
+  Variable var_string(this, MachineRepresentation::kTagged);        // String.
+
+  var_instance_type.Bind(Int32Constant(0));
+  var_string.Bind(string);
+  var_from.Bind(from);
+
+  // Make sure first argument is a string.
+
+  // Bailout if receiver is a Smi.
+  GotoIf(WordIsSmi(string), &runtime);
+
+  // Load the instance type of the {string}.
+  Node* const instance_type = LoadInstanceType(string);
+  var_instance_type.Bind(instance_type);
+
+  // Check if {string} is a String.
+  GotoIf(Int32GreaterThanOrEqual(instance_type,
+                                 Int32Constant(FIRST_NONSTRING_TYPE)),
+         &runtime);
+
+  // Make sure that both from and to are non-negative smis.
+
+  GotoUnless(WordIsPositiveSmi(from), &runtime);
+  GotoUnless(WordIsPositiveSmi(to), &runtime);
+
+  Node* const substr_length = SmiSub(to, from);
+  Node* const string_length = LoadStringLength(string);
+
+  // Begin dispatching based on substring length.
+
+  Label original_string_or_invalid_length(this);
+  GotoIf(SmiAboveOrEqual(substr_length, string_length),
+         &original_string_or_invalid_length);
+
+  // A real substring (substr_length < string_length).
+
+  Label single_char(this);
+  GotoIf(SmiEqual(substr_length, SmiConstant(Smi::FromInt(1))), &single_char);
+
+  // TODO(jgruber): Add an additional case for substring of length == 0?
+
+  // Deal with different string types: update the index if necessary
+  // and put the underlying string into var_string.
+
+  // If the string is not indirect, it can only be sequential or external.
+  STATIC_ASSERT(kIsIndirectStringMask == (kSlicedStringTag & kConsStringTag));
+  STATIC_ASSERT(kIsIndirectStringMask != 0);
+  Label underlying_unpacked(this);
+  GotoIf(Word32Equal(
+             Word32And(instance_type, Int32Constant(kIsIndirectStringMask)),
+             Int32Constant(0)),
+         &underlying_unpacked);
+
+  // The subject string is either a sliced or cons string.
+
+  Label sliced_string(this);
+  GotoIf(Word32NotEqual(
+             Word32And(instance_type, Int32Constant(kSlicedNotConsMask)),
+             Int32Constant(0)),
+         &sliced_string);
+
+  // Cons string.  Check whether it is flat, then fetch first part.
+  // Flat cons strings have an empty second part.
+  {
+    GotoIf(WordNotEqual(LoadObjectField(string, ConsString::kSecondOffset),
+                        EmptyStringConstant()),
+           &runtime);
+
+    Node* first_string_part = LoadObjectField(string, ConsString::kFirstOffset);
+    var_string.Bind(first_string_part);
+    var_instance_type.Bind(LoadInstanceType(first_string_part));
+
+    Goto(&underlying_unpacked);
+  }
+
+  Bind(&sliced_string);
+  {
+    // Fetch parent and correct start index by offset.
+    Node* sliced_offset = LoadObjectField(string, SlicedString::kOffsetOffset);
+    var_from.Bind(SmiAdd(from, sliced_offset));
+
+    Node* slice_parent = LoadObjectField(string, SlicedString::kParentOffset);
+    var_string.Bind(slice_parent);
+
+    Node* slice_parent_instance_type = LoadInstanceType(slice_parent);
+    var_instance_type.Bind(slice_parent_instance_type);
+
+    Goto(&underlying_unpacked);
+  }
+
+  // The subject string can only be external or sequential string of either
+  // encoding at this point.
+  Label external_string(this);
+  Bind(&underlying_unpacked);
+  {
+    if (FLAG_string_slices) {
+      Label copy_routine(this);
+
+      // Short slice.  Copy instead of slicing.
+      GotoIf(SmiLessThan(substr_length,
+                         SmiConstant(Smi::FromInt(SlicedString::kMinLength))),
+             &copy_routine);
+
+      // Allocate new sliced string.
+
+      Label two_byte_slice(this);
+      STATIC_ASSERT((kStringEncodingMask & kOneByteStringTag) != 0);
+      STATIC_ASSERT((kStringEncodingMask & kTwoByteStringTag) == 0);
+
+      Counters* counters = isolate()->counters();
+      IncrementCounter(counters->sub_string_native(), 1);
+
+      GotoIf(Word32Equal(Word32And(var_instance_type.value(),
+                                   Int32Constant(kStringEncodingMask)),
+                         Int32Constant(0)),
+             &two_byte_slice);
+
+      var_result.Bind(AllocateSlicedOneByteString(
+          substr_length, var_string.value(), var_from.value()));
+      Goto(&end);
+
+      Bind(&two_byte_slice);
+
+      var_result.Bind(AllocateSlicedTwoByteString(
+          substr_length, var_string.value(), var_from.value()));
+      Goto(&end);
+
+      Bind(&copy_routine);
+    }
+
+    // The subject string can only be external or sequential string of either
+    // encoding at this point.
+    STATIC_ASSERT(kExternalStringTag != 0);
+    STATIC_ASSERT(kSeqStringTag == 0);
+    GotoUnless(Word32Equal(Word32And(var_instance_type.value(),
+                                     Int32Constant(kExternalStringTag)),
+                           Int32Constant(0)),
+               &external_string);
+
+    var_result.Bind(AllocAndCopyStringCharacters(
+        this, context, var_string.value(), var_instance_type.value(),
+        var_from.value(), substr_length));
+
+    Counters* counters = isolate()->counters();
+    IncrementCounter(counters->sub_string_native(), 1);
+
+    Goto(&end);
+  }
+
+  // Handle external string.
+  Bind(&external_string);
+  {
+    // Rule out short external strings.
+    STATIC_ASSERT(kShortExternalStringTag != 0);
+    GotoIf(Word32NotEqual(Word32And(var_instance_type.value(),
+                                    Int32Constant(kShortExternalStringMask)),
+                          Int32Constant(0)),
+           &runtime);
+
+    // Move the pointer so that offset-wise, it looks like a sequential string.
+    STATIC_ASSERT(SeqTwoByteString::kHeaderSize ==
+                  SeqOneByteString::kHeaderSize);
+
+    Node* resource_data = LoadObjectField(var_string.value(),
+                                          ExternalString::kResourceDataOffset);
+    Node* const fake_sequential_string = IntPtrSub(
+        resource_data,
+        IntPtrConstant(SeqTwoByteString::kHeaderSize - kHeapObjectTag));
+
+    var_result.Bind(AllocAndCopyStringCharacters(
+        this, context, fake_sequential_string, var_instance_type.value(),
+        var_from.value(), substr_length));
+
+    Counters* counters = isolate()->counters();
+    IncrementCounter(counters->sub_string_native(), 1);
+
+    Goto(&end);
+  }
+
+  // Substrings of length 1 are generated through CharCodeAt and FromCharCode.
+  Bind(&single_char);
+  {
+    Node* char_code = StringCharCodeAt(var_string.value(), var_from.value());
+    var_result.Bind(StringFromCharCode(char_code));
+    Goto(&end);
+  }
+
+  Bind(&original_string_or_invalid_length);
+  {
+    // Longer than original string's length or negative: unsafe arguments.
+    GotoIf(SmiAbove(substr_length, string_length), &runtime);
+
+    // Equal length - check if {from, to} == {0, str.length}.
+    GotoIf(SmiAbove(from, SmiConstant(Smi::FromInt(0))), &runtime);
+
+    // Return the original string (substr_length == string_length).
+
+    Counters* counters = isolate()->counters();
+    IncrementCounter(counters->sub_string_native(), 1);
+
+    var_result.Bind(string);
+    Goto(&end);
+  }
+
+  // Fall back to a runtime call.
+  Bind(&runtime);
+  {
+    var_result.Bind(
+        CallRuntime(Runtime::kSubString, context, string, from, to));
+    Goto(&end);
+  }
+
+  Bind(&end);
+  return var_result.value();
+}
+
 Node* CodeStubAssembler::StringFromCodePoint(compiler::Node* codepoint,
                                              UnicodeEncoding encoding) {
   Variable var_result(this, MachineRepresentation::kTagged);