Revert of Internalize strings in-place

src/x64/macro-assembler-x64.cc

Index: src/x64/macro-assembler-x64.cc
diff --git a/src/x64/macro-assembler-x64.cc b/src/x64/macro-assembler-x64.cc
index 26a3dae1c646632481657f937a30e867672ecbc6..d695d0ed901e2570e5dc3773d483a4dffc17d454 100644
--- a/src/x64/macro-assembler-x64.cc
+++ b/src/x64/macro-assembler-x64.cc
@@ -2540,12 +2540,10 @@
   andl(scratch1, Immediate(kFlatOneByteStringMask));
   andl(scratch2, Immediate(kFlatOneByteStringMask));
   // Interleave the bits to check both scratch1 and scratch2 in one test.
-  const int kShift = 8;
-  DCHECK_EQ(0, kFlatOneByteStringMask & (kFlatOneByteStringMask << kShift));
-  shlp(scratch2, Immediate(kShift));
-  orp(scratch1, scratch2);
+  DCHECK_EQ(0, kFlatOneByteStringMask & (kFlatOneByteStringMask << 3));
+  leap(scratch1, Operand(scratch1, scratch2, times_8, 0));
   cmpl(scratch1,
-       Immediate(kFlatOneByteStringTag + (kFlatOneByteStringTag << kShift)));
+       Immediate(kFlatOneByteStringTag + (kFlatOneByteStringTag << 3)));
   j(not_equal, on_fail, near_jump);
 }