Tentative implementation of string slices (hidden under the flag --string-slices).

src/x64/code-stubs-x64.cc

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 2285 matching lines @@
   // Ensure that a RegExp stack is allocated.
   Isolate* isolate = masm->isolate();
   ExternalReference address_of_regexp_stack_memory_address =
       ExternalReference::address_of_regexp_stack_memory_address(isolate);
   ExternalReference address_of_regexp_stack_memory_size =
       ExternalReference::address_of_regexp_stack_memory_size(isolate);
   __ Load(kScratchRegister, address_of_regexp_stack_memory_size);
   __ testq(kScratchRegister, kScratchRegister);
   __ j(zero, &runtime);
 
-
   // Check that the first argument is a JSRegExp object.
   __ movq(rax, Operand(rsp, kJSRegExpOffset));
   __ JumpIfSmi(rax, &runtime);
   __ CmpObjectType(rax, JS_REGEXP_TYPE, kScratchRegister);
   __ j(not_equal, &runtime);
   // Check that the RegExp has been compiled (data contains a fixed array).
   __ movq(rax, FieldOperand(rax, JSRegExp::kDataOffset));
   if (FLAG_debug_code) {
     Condition is_smi = masm->CheckSmi(rax);
     __ Check(NegateCondition(is_smi),
@@ skipping 50 matching lines @@
                  Heap::kFixedArrayMapRootIndex);
   __ j(not_equal, &runtime);
   // Check that the last match info has space for the capture registers and the
   // additional information. Ensure no overflow in add.
   STATIC_ASSERT(FixedArray::kMaxLength < kMaxInt - FixedArray::kLengthOffset);
   __ SmiToInteger32(rdi, FieldOperand(rbx, FixedArray::kLengthOffset));
   __ addl(rdx, Immediate(RegExpImpl::kLastMatchOverhead));
   __ cmpl(rdx, rdi);
   __ j(greater, &runtime);
 
+  // Reset offset for possibly sliced string.
+  __ Set(r14, 0);
   // rax: RegExp data (FixedArray)
   // Check the representation and encoding of the subject string.
   Label seq_ascii_string, seq_two_byte_string, check_code;
   __ movq(rdi, Operand(rsp, kSubjectOffset));
+  // Make a copy of the original subject string.
+  __ movq(r15, rdi);
   __ movq(rbx, FieldOperand(rdi, HeapObject::kMapOffset));
   __ movzxbl(rbx, FieldOperand(rbx, Map::kInstanceTypeOffset));
   // First check for flat two byte string.
   __ andb(rbx, Immediate(
       kIsNotStringMask | kStringRepresentationMask | kStringEncodingMask));
   STATIC_ASSERT((kStringTag | kSeqStringTag | kTwoByteStringTag) == 0);
   __ j(zero, &seq_two_byte_string, Label::kNear);
   // Any other flat string must be a flat ascii string.
-  __ testb(rbx, Immediate(kIsNotStringMask | kStringRepresentationMask));
+  __ andb(rbx, Immediate(kIsNotStringMask | kStringRepresentationMask));
   __ j(zero, &seq_ascii_string, Label::kNear);
 
-  // Check for flat cons string.
+  // Check for flat cons string or sliced string.
   // A flat cons string is a cons string where the second part is the empty
   // string. In that case the subject string is just the first part of the cons
   // string. Also in this case the first part of the cons string is known to be
   // a sequential string or an external string.
-  STATIC_ASSERT(kExternalStringTag !=0);
-  STATIC_ASSERT((kConsStringTag & kExternalStringTag) == 0);
-  __ testb(rbx, Immediate(kIsNotStringMask | kExternalStringTag));
-  __ j(not_zero, &runtime);
-  // String is a cons string.
+  // In the case of a sliced string its offset has to be taken into account.
+  Label cons_string, check_encoding;
+  STATIC_ASSERT((kConsStringTag < kExternalStringTag));
+  STATIC_ASSERT((kSlicedStringTag > kExternalStringTag));
+  __ cmpq(rbx, Immediate(kExternalStringTag));
+  __ j(less, &cons_string, Label::kNear);
+  __ j(equal, &runtime);
+
+  // String is sliced.
+  __ SmiToInteger32(r14, FieldOperand(rdi, SlicedString::kOffsetOffset));
+  __ movq(rdi, FieldOperand(rdi, SlicedString::kParentOffset));
+  // r14: slice offset
+  // r15: original subject string
+  // rdi: parent string
+  __ jmp(&check_encoding, Label::kNear);
+  // String is a cons string, check whether it is flat.
+  __ bind(&cons_string);
   __ CompareRoot(FieldOperand(rdi, ConsString::kSecondOffset),
                  Heap::kEmptyStringRootIndex);
   __ j(not_equal, &runtime);
   __ movq(rdi, FieldOperand(rdi, ConsString::kFirstOffset));
+  // rdi: first part of cons string or parent of sliced string.
+  // rbx: map of first part of cons string or map of parent of sliced string.
+  // Is first part of cons or parent of slice a flat two byte string?
+  __ bind(&check_encoding);
   __ movq(rbx, FieldOperand(rdi, HeapObject::kMapOffset));
-  // String is a cons string with empty second part.
-  // rdi: first part of cons string.
-  // rbx: map of first part of cons string.
-  // Is first part a flat two byte string?
   __ testb(FieldOperand(rbx, Map::kInstanceTypeOffset),
            Immediate(kStringRepresentationMask | kStringEncodingMask));
   STATIC_ASSERT((kSeqStringTag | kTwoByteStringTag) == 0);
   __ j(zero, &seq_two_byte_string, Label::kNear);
   // Any other flat string must be ascii.
   __ testb(FieldOperand(rbx, Map::kInstanceTypeOffset),
            Immediate(kStringRepresentationMask));
   __ j(not_zero, &runtime);
 
   __ bind(&seq_ascii_string);
@@ skipping 76 matching lines @@
   Register arg3 = rdx;
   Register arg2 = rsi;
   Register arg1 = rdi;
 #endif
 
   // Keep track on aliasing between argX defined above and the registers used.
   // rdi: subject string
   // rbx: previous index
   // rcx: encoding of subject string (1 if ascii 0 if two_byte);
   // r11: code
+  // r14: slice offset
+  // r15: original subject string
+
+  // Argument 2: Previous index.
+  __ movq(arg2, rbx);
 
   // Argument 4: End of string data
   // Argument 3: Start of string data
-  Label setup_two_byte, setup_rest;
+  Label setup_two_byte, setup_rest, got_length, length_not_from_slice;
+  // Prepare start and end index of the input.
+  // Load the length from the original sliced string if that is the case.
+  __ addq(rbx, r14);
+  __ SmiToInteger32(arg3, FieldOperand(r15, String::kLengthOffset));
+  __ addq(r14, arg3);  // Using arg3 as scratch.
+
+  // rbx: start index of the input
+  // r14: end index of the input
+  // r15: original subject string
   __ testb(rcx, rcx);  // Last use of rcx as encoding of subject string.
   __ j(zero, &setup_two_byte, Label::kNear);
-  __ SmiToInteger32(rcx, FieldOperand(rdi, String::kLengthOffset));
-  __ lea(arg4, FieldOperand(rdi, rcx, times_1, SeqAsciiString::kHeaderSize));
+  __ lea(arg4, FieldOperand(rdi, r14, times_1, SeqAsciiString::kHeaderSize));
   __ lea(arg3, FieldOperand(rdi, rbx, times_1, SeqAsciiString::kHeaderSize));
   __ jmp(&setup_rest, Label::kNear);
   __ bind(&setup_two_byte);
-  __ SmiToInteger32(rcx, FieldOperand(rdi, String::kLengthOffset));
-  __ lea(arg4, FieldOperand(rdi, rcx, times_2, SeqTwoByteString::kHeaderSize));
+  __ lea(arg4, FieldOperand(rdi, r14, times_2, SeqTwoByteString::kHeaderSize));
   __ lea(arg3, FieldOperand(rdi, rbx, times_2, SeqTwoByteString::kHeaderSize));
+  __ bind(&setup_rest);
 
-  __ bind(&setup_rest);
-  // Argument 2: Previous index.
-  __ movq(arg2, rbx);
-
-  // Argument 1: Subject string.
-#ifdef _WIN64
-  __ movq(arg1, rdi);
-#else
-  // Already there in AMD64 calling convention.
-  ASSERT(arg1.is(rdi));
-  USE(arg1);
-#endif
+  // Argument 1: Original subject string.
+  // The original subject is in the previous stack frame. Therefore we have to
+  // use rbp, which points exactly to one pointer size below the previous rsp.
+  // (Because creating a new stack frame pushes the previous rbp onto the stack
+  // and thereby moves up rsp by one kPointerSize.)
+  __ movq(arg1, r15);
 
   // Locate the code entry and call it.
   __ addq(r11, Immediate(Code::kHeaderSize - kHeapObjectTag));
   __ call(r11);
 
   __ LeaveApiExitFrame();
 
   // Check the result.
   Label success;
   Label exception;
@@ skipping 1229 matching lines @@
 }
 
 
 // -------------------------------------------------------------------------
 // StringCharCodeAtGenerator
 
 void StringCharCodeAtGenerator::GenerateFast(MacroAssembler* masm) {
   Label flat_string;
   Label ascii_string;
   Label got_char_code;
+  Label sliced_string;
 
   // If the receiver is a smi trigger the non-string case.
   __ JumpIfSmi(object_, receiver_not_string_);
 
   // Fetch the instance type of the receiver into result register.
   __ movq(result_, FieldOperand(object_, HeapObject::kMapOffset));
   __ movzxbl(result_, FieldOperand(result_, Map::kInstanceTypeOffset));
   // If the receiver is not a string trigger the non-string case.
   __ testb(result_, Immediate(kIsNotStringMask));
   __ j(not_zero, receiver_not_string_);
 
   // If the index is non-smi trigger the non-smi case.
   __ JumpIfNotSmi(index_, &index_not_smi_);
 
   // Put smi-tagged index into scratch register.
   __ movq(scratch_, index_);
   __ bind(&got_smi_index_);
 
   // Check for index out of range.
   __ SmiCompare(scratch_, FieldOperand(object_, String::kLengthOffset));
   __ j(above_equal, index_out_of_range_);
 
   // We need special handling for non-flat strings.
   STATIC_ASSERT(kSeqStringTag == 0);
   __ testb(result_, Immediate(kStringRepresentationMask));
   __ j(zero, &flat_string);
 
   // Handle non-flat strings.
-  __ testb(result_, Immediate(kIsConsStringMask));
-  __ j(zero, &call_runtime_);
+  __ and_(result_, Immediate(kStringRepresentationMask));
+  STATIC_ASSERT((kConsStringTag < kExternalStringTag));
+  STATIC_ASSERT((kSlicedStringTag > kExternalStringTag));
+  __ cmpb(result_, Immediate(kExternalStringTag));
+  __ j(greater, &sliced_string);
+  __ j(equal, &call_runtime_);
 
   // ConsString.
   // Check whether the right hand side is the empty string (i.e. if
   // this is really a flat string in a cons string). If that is not
   // the case we would rather go to the runtime system now to flatten
   // the string.
+  Label assure_seq_string;
   __ CompareRoot(FieldOperand(object_, ConsString::kSecondOffset),
                  Heap::kEmptyStringRootIndex);
   __ j(not_equal, &call_runtime_);
   // Get the first of the two strings and load its instance type.
   __ movq(object_, FieldOperand(object_, ConsString::kFirstOffset));
+  __ jmp(&assure_seq_string, Label::kNear);
+
+  // SlicedString, unpack and add offset.
+  __ bind(&sliced_string);
+  __ addq(scratch_, FieldOperand(object_, SlicedString::kOffsetOffset));
+  __ movq(object_, FieldOperand(object_, SlicedString::kParentOffset));
+
+  __ bind(&assure_seq_string);
   __ movq(result_, FieldOperand(object_, HeapObject::kMapOffset));
   __ movzxbl(result_, FieldOperand(result_, Map::kInstanceTypeOffset));
   // If the first cons component is also non-flat, then go to runtime.
   STATIC_ASSERT(kSeqStringTag == 0);
   __ testb(result_, Immediate(kStringRepresentationMask));
   __ j(not_zero, &call_runtime_);
+  __ jmp(&flat_string);
 
   // Check for 1-byte or 2-byte string.
   __ bind(&flat_string);
   STATIC_ASSERT(kAsciiStringTag != 0);
   __ testb(result_, Immediate(kStringEncodingMask));
   __ j(not_zero, &ascii_string);
 
   // 2-byte string.
   // Load the 2-byte character code into the result register.
   __ SmiToInteger32(scratch_, scratch_);
@@ skipping 290 matching lines @@
   __ bind(&string_add_flat_result);
   __ SmiToInteger32(rbx, rbx);
   __ movl(rcx, r8);
   __ and_(rcx, Immediate(kStringRepresentationMask));
   __ cmpl(rcx, Immediate(kExternalStringTag));
   __ j(equal, &string_add_runtime);
   __ movl(rcx, r9);
   __ and_(rcx, Immediate(kStringRepresentationMask));
   __ cmpl(rcx, Immediate(kExternalStringTag));
   __ j(equal, &string_add_runtime);
+  // We cannot encounter sliced strings here since:
+  STATIC_ASSERT(SlicedString::kMinLength >= String::kMinNonFlatLength);
   // Now check if both strings are ascii strings.
   // rax: first string
   // rbx: length of resulting flat string
   // rdx: second string
   // r8: instance type of first string
   // r9: instance type of second string
   Label non_ascii_string_add_flat_result;
   STATIC_ASSERT(kStringEncodingMask == kAsciiStringTag);
   __ testl(r8, Immediate(kAsciiStringTag));
   __ j(zero, &non_ascii_string_add_flat_result);
@@ skipping 372 matching lines @@
   // if (hash == 0) hash = 27;
   Label hash_not_zero;
   __ j(not_zero, &hash_not_zero);
   __ Set(hash, 27);
   __ bind(&hash_not_zero);
 }
 
 void SubStringStub::Generate(MacroAssembler* masm) {
   Label runtime;
 
+  if (FLAG_string_slices) {
+    __ jmp(&runtime);
+  }
   // Stack frame on entry.
   //  rsp[0]: return address
   //  rsp[8]: to
   //  rsp[16]: from
   //  rsp[24]: string
 
   const int kToOffset = 1 * kPointerSize;
   const int kFromOffset = kToOffset + kPointerSize;
   const int kStringOffset = kFromOffset + kPointerSize;
   const int kArgumentsSize = (kStringOffset + kPointerSize) - kToOffset;
@@ skipping 741 matching lines @@
   __ Drop(1);
   __ ret(2 * kPointerSize);
 }
 
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64