Revert of Experimental support for RegExp lookbehind.

src/regexp/interpreter-irregexp.cc

Index: src/regexp/interpreter-irregexp.cc
diff --git a/src/regexp/interpreter-irregexp.cc b/src/regexp/interpreter-irregexp.cc
index fb6045e5d790468dd96ab08b3083bbea4f3c5f9e..afc31a3d57bbc86d122fba489bba2bb18675b86a 100644
--- a/src/regexp/interpreter-irregexp.cc
+++ b/src/regexp/interpreter-irregexp.cc
@@ -270,7 +270,7 @@
         break;
       BYTECODE(LOAD_CURRENT_CHAR) {
         int pos = current + (insn >> BYTECODE_SHIFT);
-        if (pos >= subject.length() || pos < 0) {
+        if (pos >= subject.length()) {
           pc = code_base + Load32Aligned(pc + 4);
         } else {
           current_char = subject[pos];
@@ -286,7 +286,7 @@
       }
       BYTECODE(LOAD_2_CURRENT_CHARS) {
         int pos = current + (insn >> BYTECODE_SHIFT);
-        if (pos + 2 > subject.length() || pos < 0) {
+        if (pos + 2 > subject.length()) {
           pc = code_base + Load32Aligned(pc + 4);
         } else {
           Char next = subject[pos + 1];
@@ -306,7 +306,7 @@
       BYTECODE(LOAD_4_CURRENT_CHARS) {
         DCHECK(sizeof(Char) == 1);
         int pos = current + (insn >> BYTECODE_SHIFT);
-        if (pos + 4 > subject.length() || pos < 0) {
+        if (pos + 4 > subject.length()) {
           pc = code_base + Load32Aligned(pc + 4);
         } else {
           Char next1 = subject[pos + 1];
@@ -497,59 +497,46 @@
       BYTECODE(CHECK_NOT_BACK_REF) {
         int from = registers[insn >> BYTECODE_SHIFT];
         int len = registers[(insn >> BYTECODE_SHIFT) + 1] - from;
-        if (from >= 0 && len > 0) {
-          if (current + len > subject.length() ||
-              CompareChars(&subject[from], &subject[current], len) != 0) {
-            pc = code_base + Load32Aligned(pc + 4);
-            break;
+        if (from < 0 || len <= 0) {
+          pc += BC_CHECK_NOT_BACK_REF_LENGTH;
+          break;
+        }
+        if (current + len > subject.length()) {
+          pc = code_base + Load32Aligned(pc + 4);
+          break;
+        } else {
+          int i;
+          for (i = 0; i < len; i++) {
+            if (subject[from + i] != subject[current + i]) {
+              pc = code_base + Load32Aligned(pc + 4);
+              break;
+            }
           }
+          if (i < len) break;
           current += len;
         }
         pc += BC_CHECK_NOT_BACK_REF_LENGTH;
-        break;
-      }
-      BYTECODE(CHECK_NOT_BACK_REF_BACKWARD) {
-        int from = registers[insn >> BYTECODE_SHIFT];
-        int len = registers[(insn >> BYTECODE_SHIFT) + 1] - from;
-        if (from >= 0 && len > 0) {
-          if (current - len < 0 ||
-              CompareChars(&subject[from], &subject[current - len], len) != 0) {
-            pc = code_base + Load32Aligned(pc + 4);
-            break;
-          }
-          current -= len;
-        }
-        pc += BC_CHECK_NOT_BACK_REF_BACKWARD_LENGTH;
         break;
       }
       BYTECODE(CHECK_NOT_BACK_REF_NO_CASE) {
         int from = registers[insn >> BYTECODE_SHIFT];
         int len = registers[(insn >> BYTECODE_SHIFT) + 1] - from;
-        if (from >= 0 && len > 0) {
-          if (current + len > subject.length() ||
-              !BackRefMatchesNoCase(isolate->interp_canonicalize_mapping(),
-                                    from, current, len, subject)) {
+        if (from < 0 || len <= 0) {
+          pc += BC_CHECK_NOT_BACK_REF_NO_CASE_LENGTH;
+          break;
+        }
+        if (current + len > subject.length()) {
+          pc = code_base + Load32Aligned(pc + 4);
+          break;
+        } else {
+          if (BackRefMatchesNoCase(isolate->interp_canonicalize_mapping(),
+                                   from, current, len, subject)) {
+            current += len;
+            pc += BC_CHECK_NOT_BACK_REF_NO_CASE_LENGTH;
+          } else {
             pc = code_base + Load32Aligned(pc + 4);
-            break;
           }
-          current += len;
-        }
-        pc += BC_CHECK_NOT_BACK_REF_NO_CASE_LENGTH;
-        break;
-      }
-      BYTECODE(CHECK_NOT_BACK_REF_NO_CASE_BACKWARD) {
-        int from = registers[insn >> BYTECODE_SHIFT];
-        int len = registers[(insn >> BYTECODE_SHIFT) + 1] - from;
-        if (from >= 0 && len > 0) {
-          if (current - len < 0 ||
-              !BackRefMatchesNoCase(isolate->interp_canonicalize_mapping(),
-                                    from, current - len, len, subject)) {
-            pc = code_base + Load32Aligned(pc + 4);
-            break;
-          }
-          current -= len;
-        }
-        pc += BC_CHECK_NOT_BACK_REF_NO_CASE_BACKWARD_LENGTH;
+        }
         break;
       }
       BYTECODE(CHECK_AT_START)
@@ -560,7 +547,7 @@
         }
         break;
       BYTECODE(CHECK_NOT_AT_START)
-        if (current + (insn >> BYTECODE_SHIFT) == 0) {
+        if (current == 0) {
           pc += BC_CHECK_NOT_AT_START_LENGTH;
         } else {
           pc = code_base + Load32Aligned(pc + 4);