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

src/ia32/code-stubs-ia32.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 4809 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.
   STATIC_ASSERT(kSmiTag == 0);
   __ JumpIfSmi(object_, receiver_not_string_);
 
   // Fetch the instance type of the receiver into result register.
   __ mov(result_, FieldOperand(object_, HeapObject::kMapOffset));
   __ movzx_b(result_, FieldOperand(result_, Map::kInstanceTypeOffset));
   // If the receiver is not a string trigger the non-string case.
   __ test(result_, Immediate(kIsNotStringMask));
@@ skipping 10 matching lines @@
   // Check for index out of range.
   __ cmp(scratch_, FieldOperand(object_, String::kLengthOffset));
   __ j(above_equal, index_out_of_range_);
 
   // We need special handling for non-flat strings.
   STATIC_ASSERT(kSeqStringTag == 0);
   __ test(result_, Immediate(kStringRepresentationMask));
   __ j(zero, &flat_string);
 
   // Handle non-flat strings.
-  __ test(result_, Immediate(kIsConsStringMask));
-  __ j(zero, &call_runtime_);
+  __ and_(result_, kStringRepresentationMask);
+  __ cmp(result_, kSlicedStringTag);
+  __ j(equal, &sliced_string);
+  __ cmp(result_, kExternalStringTag);
+  __ 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.
   __ cmp(FieldOperand(object_, ConsString::kSecondOffset),
          Immediate(masm->isolate()->factory()->empty_string()));
   __ j(not_equal, &call_runtime_);
   // Get the first of the two strings and load its instance type.
   __ mov(object_, FieldOperand(object_, ConsString::kFirstOffset));
   __ mov(result_, FieldOperand(object_, HeapObject::kMapOffset));
   __ movzx_b(result_, FieldOperand(result_, Map::kInstanceTypeOffset));
   // If the first cons component is also non-flat, then go to runtime.
   STATIC_ASSERT(kSeqStringTag == 0);
   __ test(result_, Immediate(kStringRepresentationMask));
   __ j(not_zero, &call_runtime_);
+  __ jmp(&flat_string);
+
+  // SlicedString, unpack and add offset.
+  __ bind(&sliced_string);
+  __ add(scratch_, FieldOperand(object_, SlicedString::kOffsetOffset));
+  __ mov(object_, FieldOperand(object_, SlicedString::kParentOffset));
+  __ mov(result_, FieldOperand(object_, HeapObject::kMapOffset));
+  __ movzx_b(result_, FieldOperand(result_, Map::kInstanceTypeOffset));
 
   // Check for 1-byte or 2-byte string.
   __ bind(&flat_string);
   STATIC_ASSERT(kAsciiStringTag != 0);
   __ test(result_, Immediate(kStringEncodingMask));
   __ j(not_zero, &ascii_string);
 
   // 2-byte string.
   // Load the 2-byte character code into the result register.
   STATIC_ASSERT(kSmiTag == 0 && kSmiTagSize == 1);
@@ skipping 305 matching lines @@
   __ mov(ecx, FieldOperand(eax, HeapObject::kMapOffset));
   __ movzx_b(ecx, FieldOperand(ecx, Map::kInstanceTypeOffset));
   __ and_(ecx, kStringRepresentationMask);
   __ cmp(ecx, kExternalStringTag);
   __ j(equal, &string_add_runtime);
   __ mov(ecx, FieldOperand(edx, HeapObject::kMapOffset));
   __ movzx_b(ecx, FieldOperand(ecx, Map::kInstanceTypeOffset));
   __ and_(ecx, kStringRepresentationMask);
   __ cmp(ecx, 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.
   // eax: first string
   // ebx: length of resulting flat string as a smi
   // edx: second string
   Label non_ascii_string_add_flat_result;
   STATIC_ASSERT(kStringEncodingMask == kAsciiStringTag);
   __ mov(ecx, FieldOperand(eax, HeapObject::kMapOffset));
   __ test_b(FieldOperand(ecx, Map::kInstanceTypeOffset), kAsciiStringTag);
   __ j(zero, &non_ascii_string_add_flat_result);
   __ mov(ecx, FieldOperand(edx, HeapObject::kMapOffset));
@@ skipping 390 matching lines @@
   Label hash_not_zero;
   __ test(hash, Operand(hash));
   __ j(not_zero, &hash_not_zero, Label::kNear);
   __ mov(hash, Immediate(27));
   __ bind(&hash_not_zero);
 }
 
 
 void SubStringStub::Generate(MacroAssembler* masm) {
   Label runtime;
 

[Yang, 2011/07/27 11:51:58]

Do not create string slice unless experimental flag is set.

+  if (FLAG_string_slices) {
+    __ jmp(&runtime);
+  }
   // Stack frame on entry.
   //  esp[0]: return address
   //  esp[4]: to
   //  esp[8]: from
   //  esp[12]: string
 
   // Make sure first argument is a string.
   __ mov(eax, Operand(esp, 3 * kPointerSize));
   STATIC_ASSERT(kSmiTag == 0);
   __ JumpIfSmi(eax, &runtime);
@@ skipping 756 matching lines @@
   __ Drop(1);
   __ ret(2 * kPointerSize);
 }
 
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_IA32