[regexp] Update lastIndex semantics in RegExpBuiltinExec

Updated according to the recent spec change at
https://github.com/tc39/ecma262/pull/798.

BUG=v8:5949

Review-Url: https://codereview.chromium.org/2681323002
Cr-Commit-Position: refs/heads/master@{#43062}

src/builtins/builtins-regexp.cc

@@ -241,6 +241,27 @@ Node* RegExpBuiltinsAssembler::RegExpPrototypeExecBodyWithoutResult(
   Node* const native_context = LoadNativeContext(context);
   Node* const string_length = LoadStringLength(string);
 
+  // Load lastIndex.
+  Variable var_lastindex(this, MachineRepresentation::kTagged);
+  {
+    Node* const regexp_lastindex = LoadLastIndex(context, regexp, is_fastpath);
+    var_lastindex.Bind(regexp_lastindex);
+
+    // Omit ToLength if lastindex is a non-negative smi.
+    Label call_tolength(this, Label::kDeferred), next(this);
+    Branch(TaggedIsPositiveSmi(regexp_lastindex), &next, &call_tolength);
+
+    Bind(&call_tolength);
+    {
+      Callable tolength_callable = CodeFactory::ToLength(isolate);
+      var_lastindex.Bind(
+          CallStub(tolength_callable, context, regexp_lastindex));
+      Goto(&next);
+    }
+
+    Bind(&next);
+  }
+
   // Check whether the regexp is global or sticky, which determines whether we
   // update last index later on.
   Node* const flags = LoadObjectField(regexp, JSRegExp::kFlagsOffset);
@@ -251,33 +272,12 @@ Node* RegExpBuiltinsAssembler::RegExpPrototypeExecBodyWithoutResult(
 
   // Grab and possibly update last index.
   Label run_exec(this);
-  Variable var_lastindex(this, MachineRepresentation::kTagged);
   {
     Label if_doupdate(this), if_dontupdate(this);
     Branch(should_update_last_index, &if_doupdate, &if_dontupdate);
 
     Bind(&if_doupdate);
     {
-      Node* const regexp_lastindex =
-          LoadLastIndex(context, regexp, is_fastpath);
-      var_lastindex.Bind(regexp_lastindex);
-
-      // Omit ToLength if lastindex is a non-negative smi.
-      {
-        Label call_tolength(this, Label::kDeferred), next(this);
-        Branch(TaggedIsPositiveSmi(regexp_lastindex), &next, &call_tolength);
-
-        Bind(&call_tolength);
-        {
-          Callable tolength_callable = CodeFactory::ToLength(isolate);
-          var_lastindex.Bind(
-              CallStub(tolength_callable, context, regexp_lastindex));
-          Goto(&next);
-        }
-
-        Bind(&next);
-      }
-
       Node* const lastindex = var_lastindex.value();
 
       Label if_isoob(this, Label::kDeferred);

test/mjsunit/regexp.js

@@ -564,21 +564,21 @@ log = [];
 re.lastIndex = fakeLastIndex;
 var result = re.exec(fakeString);
 assertEquals(["str"], result);
-assertEquals(["ts"], log);
+assertEquals(["ts", "li"], log);
 
 // Again, to check if caching interferes.
 log = [];
 re.lastIndex = fakeLastIndex;
 result = re.exec(fakeString);
 assertEquals(["str"], result);
-assertEquals(["ts"], log);
+assertEquals(["ts", "li"], log);
 
 // And one more time, just to be certain.
 log = [];
 re.lastIndex = fakeLastIndex;
 result = re.exec(fakeString);
 assertEquals(["str"], result);
-assertEquals(["ts"], log);
+assertEquals(["ts", "li"], log);
 
 // Now with a global regexp, where lastIndex is actually used.
 re = /str/g;

test/mjsunit/regress/regress-2438.js

@@ -27,20 +27,16 @@
 
 function testSideEffects(subject, re) {
   var counter = 0;
-  var expected_counter = 0;
-  const accesses_lastindex = (re.global || re.sticky);
   var side_effect_object = { valueOf: function() { return counter++; } };
   re.lastIndex = side_effect_object;
   re.exec(subject);
 
-  if (accesses_lastindex) expected_counter++;
+  assertEquals(1, counter);
-  assertEquals(expected_counter, counter);
 
   re.lastIndex = side_effect_object;
   re.test(subject);
 
-  if (accesses_lastindex) expected_counter++;
+  assertEquals(2, counter);
-  assertEquals(expected_counter, counter);
 }
 
 testSideEffects("zzzz", /a/);

test/test262/test262.status

@@ -91,6 +91,10 @@
   'built-ins/RegExp/prototype/Symbol.replace/y-init-lastindex': [FAIL],
   'built-ins/RegExp/prototype/Symbol.replace/y-set-lastindex': [FAIL],
 
+  # https://bugs.chromium.org/p/v8/issues/detail?id=5949
+  'built-ins/RegExp/prototype/exec/failure-lastindex-no-access': [FAIL],
+  'built-ins/RegExp/prototype/exec/success-lastindex-no-access': [FAIL],
+
   ###### END REGEXP SUBCLASSING SECTION ######
 
   # https://bugs.chromium.org/p/v8/issues/detail?id=4895