Revert of Internalize strings in-place

src/arm64/code-stubs-arm64.cc

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #if V8_TARGET_ARCH_ARM64
 
 #include "src/code-stubs.h"
 #include "src/api-arguments.h"
 #include "src/bootstrapper.h"
 #include "src/codegen.h"
@@ skipping 1427 matching lines @@
   //     and go to (1). Otherwise bail out to runtime.
   // (4) Sequential string.  Load regexp code according to encoding.
   // (E) Carry on.
   /// [...]
 
   // Deferred code at the end of the stub:
   // (5) Long external string?  If not, go to (7).
   // (6) External string.  Make it, offset-wise, look like a sequential string.
   //     Go to (4).
   // (7) Short external string or not a string?  If yes, bail out to runtime.
-  // (8) Sliced or thin string.  Replace subject with parent.  Go to (1).
+  // (8) Sliced string.  Replace subject with parent.  Go to (1).
 
   Label check_underlying;   // (1)
   Label seq_string;         // (4)
   Label not_seq_nor_cons;   // (5)
   Label external_string;    // (6)
   Label not_long_external;  // (7)
 
   __ Bind(&check_underlying);
   __ Ldr(x10, FieldMemOperand(subject, HeapObject::kMapOffset));
   __ Ldrb(string_type, FieldMemOperand(x10, Map::kInstanceTypeOffset));
@@ skipping 13 matching lines @@
   //                |  |   is a SeqString
   //                |  is not a short external String
   //                is a String
   STATIC_ASSERT((kStringTag | kSeqStringTag) == 0);
   STATIC_ASSERT(kShortExternalStringTag != 0);
   __ Cbz(string_representation, &seq_string);  // Go to (4).
 
   // (2) Sequential or cons?  If not, go to (5).
   STATIC_ASSERT(kConsStringTag < kExternalStringTag);
   STATIC_ASSERT(kSlicedStringTag > kExternalStringTag);
-  STATIC_ASSERT(kThinStringTag > kExternalStringTag);
   STATIC_ASSERT(kIsNotStringMask > kExternalStringTag);
   STATIC_ASSERT(kShortExternalStringTag > kExternalStringTag);
   __ Cmp(string_representation, kExternalStringTag);
   __ B(ge, &not_seq_nor_cons);  // Go to (5).
 
   // (3) Cons string.  Check that it's flat.
   __ Ldr(x10, FieldMemOperand(subject, ConsString::kSecondOffset));
   __ JumpIfNotRoot(x10, Heap::kempty_stringRootIndex, &runtime);
   // Replace subject with first string.
   __ Ldr(subject, FieldMemOperand(subject, ConsString::kFirstOffset));
   __ B(&check_underlying);
 
   // (4) Sequential string.  Load regexp code according to encoding.
   __ Bind(&seq_string);
 
   // Check that the third argument is a positive smi less than the subject
   // string length. A negative value will be greater (unsigned comparison).
   DCHECK(jssp.Is(__ StackPointer()));
   __ Peek(x10, kPreviousIndexOffset);
   __ JumpIfNotSmi(x10, &runtime);
   __ Cmp(jsstring_length, x10);
   __ B(ls, &runtime);
 
   // Argument 2 (x1): We need to load argument 2 (the previous index) into x1
   // before entering the exit frame.
   __ SmiUntag(x1, x10);
 
-  // The fourth bit determines the string encoding in string_type.
-  STATIC_ASSERT(kOneByteStringTag == 0x08);
+  // The third bit determines the string encoding in string_type.
+  STATIC_ASSERT(kOneByteStringTag == 0x04);
   STATIC_ASSERT(kTwoByteStringTag == 0x00);
-  STATIC_ASSERT(kStringEncodingMask == 0x08);
+  STATIC_ASSERT(kStringEncodingMask == 0x04);
 
   // Find the code object based on the assumptions above.
   // kDataOneByteCodeOffset and kDataUC16CodeOffset are adjacent, adds an offset
   // of kPointerSize to reach the latter.
   STATIC_ASSERT(JSRegExp::kDataOneByteCodeOffset + kPointerSize ==
                 JSRegExp::kDataUC16CodeOffset);
   __ Mov(x10, kPointerSize);
-  // We will need the encoding later: Latin1 = 0x08
+  // We will need the encoding later: Latin1 = 0x04
   //                                  UC16   = 0x00
   __ Ands(string_encoding, string_type, kStringEncodingMask);
   __ CzeroX(x10, ne);
   __ Add(x10, regexp_data, x10);
   __ Ldr(code_object, FieldMemOperand(x10, JSRegExp::kDataOneByteCodeOffset));
 
   // (E) Carry on.  String handling is done.
 
   // Check that the irregexp code has been generated for the actual string
   // encoding. If it has, the field contains a code object otherwise it contains
@@ skipping 27 matching lines @@
   // Load start of the subject string.
   __ Add(start, subject, SeqString::kHeaderSize - kHeapObjectTag);
   // Load the length from the original subject string from the previous stack
   // frame. Therefore we have to use fp, which points exactly to two pointer
   // sizes below the previous sp. (Because creating a new stack frame pushes
   // the previous fp onto the stack and decrements sp by 2 * kPointerSize.)
   __ Ldr(subject, MemOperand(fp, kSubjectOffset + 2 * kPointerSize));
   __ Ldr(length, UntagSmiFieldMemOperand(subject, String::kLengthOffset));
 
   // Handle UC16 encoding, two bytes make one character.
-  //   string_encoding: if Latin1: 0x08
+  //   string_encoding: if Latin1: 0x04
   //                    if UC16:   0x00
-  STATIC_ASSERT(kStringEncodingMask == 0x08);
-  __ Ubfx(string_encoding, string_encoding, 3, 1);
+  STATIC_ASSERT(kStringEncodingMask == 0x04);
+  __ Ubfx(string_encoding, string_encoding, 2, 1);
   __ Eor(string_encoding, string_encoding, 1);
   //   string_encoding: if Latin1: 0
   //                    if UC16:   1
 
   // Convert string positions from characters to bytes.
   // Previous index is in x1.
   __ Lsl(previous_index_in_bytes, w1, string_encoding);
   __ Lsl(length, length, string_encoding);
   __ Lsl(sliced_string_offset, sliced_string_offset, string_encoding);
 
@@ skipping 192 matching lines @@
   __ B(&seq_string);  // Go to (4).
 
   // (7) If this is a short external string or not a string, bail out to
   // runtime.
   __ Bind(&not_long_external);
   STATIC_ASSERT(kShortExternalStringTag != 0);
   __ TestAndBranchIfAnySet(string_representation,
                            kShortExternalStringMask | kIsNotStringMask,
                            &runtime);
 
-  // (8) Sliced or thin string. Replace subject with parent.
-  Label thin_string;
-  __ Cmp(string_representation, kThinStringTag);
-  __ B(eq, &thin_string);
+  // (8) Sliced string. Replace subject with parent.
   __ Ldr(sliced_string_offset,
          UntagSmiFieldMemOperand(subject, SlicedString::kOffsetOffset));
   __ Ldr(subject, FieldMemOperand(subject, SlicedString::kParentOffset));
   __ B(&check_underlying);  // Go to (1).
-
-  __ bind(&thin_string);
-  __ Ldr(subject, FieldMemOperand(subject, ThinString::kActualOffset));
-  __ B(&check_underlying);  // Go to (1).
 #endif
 }
 
 
 static void CallStubInRecordCallTarget(MacroAssembler* masm, CodeStub* stub,
                                        Register argc, Register function,
                                        Register feedback_vector, Register index,
                                        Register new_target) {
   FrameScope scope(masm, StackFrame::INTERNAL);
 
@@ skipping 2756 matching lines @@
                            kStackUnwindSpace, NULL, spill_offset,
                            return_value_operand, NULL);
 }
 
 #undef __
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_TARGET_ARCH_ARM64