Revert of Internalize strings in-place

src/x64/code-stubs-x64.cc

Index: src/x64/code-stubs-x64.cc
diff --git a/src/x64/code-stubs-x64.cc b/src/x64/code-stubs-x64.cc
index 88810e93c6aa64570fb1b123d49d6eb5cfcadcce..27c747594530b734235bac6bf8521e8f440f85fb 100644
--- a/src/x64/code-stubs-x64.cc
+++ b/src/x64/code-stubs-x64.cc
@@ -484,7 +484,7 @@ void RegExpExecStub::Generate(MacroAssembler* masm) {
   // (8) Is the external string one byte?  If yes, go to (5).
   // (9) Two byte sequential.  Load regexp code for two byte. Go to (E).
   // (10) Short external string or not a string?  If yes, bail out to runtime.
-  // (11) Sliced or thin string.  Replace subject with parent. Go to (1).
+  // (11) Sliced string.  Replace subject with parent. Go to (1).
 
   Label seq_one_byte_string /* 5 */, seq_two_byte_string /* 9 */,
       external_string /* 7 */, check_underlying /* 1 */,
@@ -514,7 +514,6 @@ void RegExpExecStub::Generate(MacroAssembler* masm) {
   // have already been covered.
   STATIC_ASSERT(kConsStringTag < kExternalStringTag);
   STATIC_ASSERT(kSlicedStringTag > kExternalStringTag);
-  STATIC_ASSERT(kThinStringTag > kExternalStringTag);
   STATIC_ASSERT(kIsNotStringMask > kExternalStringTag);
   STATIC_ASSERT(kShortExternalStringTag > kExternalStringTag);
   __ cmpp(rbx, Immediate(kExternalStringTag));
@@ -803,18 +802,11 @@ void RegExpExecStub::Generate(MacroAssembler* masm) {
   __ testb(rbx, Immediate(kIsNotStringMask | kShortExternalStringMask));
   __ j(not_zero, &runtime);
 
-  // (11) Sliced or thin string.  Replace subject with parent. Go to (1).
-  Label thin_string;
-  __ cmpl(rbx, Immediate(kThinStringTag));
-  __ j(equal, &thin_string, Label::kNear);
+  // (11) Sliced string.  Replace subject with parent. Go to (1).
   // Load offset into r14 and replace subject string with parent.
   __ SmiToInteger32(r14, FieldOperand(rdi, SlicedString::kOffsetOffset));
   __ movp(rdi, FieldOperand(rdi, SlicedString::kParentOffset));
   __ jmp(&check_underlying);
-
-  __ bind(&thin_string);
-  __ movp(rdi, FieldOperand(rdi, ThinString::kActualOffset));
-  __ jmp(&check_underlying);
 #endif  // V8_INTERPRETED_REGEXP
 }