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

src/ia32/lithium-codegen-ia32.cc

Index: src/ia32/lithium-codegen-ia32.cc
diff --git a/src/ia32/lithium-codegen-ia32.cc b/src/ia32/lithium-codegen-ia32.cc
index e2a18eb2fc96d8d0ec43548a0f3b6547cd4e4777..cb99f170c958f5128d77b8fc7cc7890d085ccb86 100644
--- a/src/ia32/lithium-codegen-ia32.cc
+++ b/src/ia32/lithium-codegen-ia32.cc
@@ -3139,6 +3139,7 @@ void LCodeGen::DoStringCharCodeAt(LStringCharCodeAt* instr) {
 
   Register string = ToRegister(instr->string());
   Register index = no_reg;
+  Register offset = ToRegister(instr->TempAt(0));
   int const_index = -1;
   if (instr->index()->IsConstantOperand()) {
     const_index = ToInteger32(LConstantOperand::cast(instr->index()));
@@ -3161,7 +3162,7 @@ void LCodeGen::DoStringCharCodeAt(LStringCharCodeAt* instr) {
   DeferredStringCharCodeAt* deferred =
       new DeferredStringCharCodeAt(this, instr);
 
-  Label flat_string, ascii_string, done;
+  Label flat_string, ascii_string, cons_string, sliced_ascii_string, done;
 
   // Fetch the instance type of the receiver into result register.
   __ mov(result, FieldOperand(string, HeapObject::kMapOffset));
@@ -3173,14 +3174,46 @@ void LCodeGen::DoStringCharCodeAt(LStringCharCodeAt* instr) {
   __ j(zero, &flat_string, Label::kNear);
 
   // Handle non-flat strings.
-  __ test(result, Immediate(kIsConsStringMask));
-  __ j(zero, deferred->entry());
+  __ and_(result, kStringRepresentationMask);
+  __ cmp(result, kConsStringTag);
+  __ j(equal, &cons_string, Label::kNear);
+  __ cmp(result, kExternalStringTag);
+  __ j(equal, deferred->entry());
+
+  // SlicedString.
+  // Unpack slice, add offset and retrieve the result char.
+  __ mov(offset, FieldOperand(string, SlicedString::kOffsetOffset));
+  __ SmiUntag(offset);
+  if (instr->index()->IsConstantOperand()) {
+    __ add(Operand(offset), Immediate(const_index));
+  } else {
+    __ add(offset, Operand(index));
+  }
+  __ mov(string, FieldOperand(string, SlicedString::kParentOffset));
+  __ mov(result, FieldOperand(string, HeapObject::kMapOffset));
+  __ movzx_b(result, FieldOperand(result, Map::kInstanceTypeOffset));
+  // Check for ASCII or two-byte string.
+  STATIC_ASSERT(kAsciiStringTag != 0);
+  __ test(result, Immediate(kStringEncodingMask));
+  __ j(not_zero, &sliced_ascii_string, Label::kNear);
+  __ movzx_w(result, FieldOperand(string,
+                                  offset,
+                                  times_2,
+                                  SeqTwoByteString::kHeaderSize));
+  __ jmp(&done, Label::kNear);
+  __ bind(&sliced_ascii_string);
+  __ movzx_b(result, FieldOperand(string,
+                                  offset,
+                                  times_1,
+                                  SeqAsciiString::kHeaderSize));
+  __ jmp(&done, Label::kNear);
 
   // 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.
+  __ bind(&cons_string);
   __ cmp(FieldOperand(string, ConsString::kSecondOffset),
          Immediate(factory()->empty_string()));
   __ j(not_equal, deferred->entry());