[parser] Eliminate ExpressionClassifier::MergeNonPatterns

A minor change in the logic of expression classifiers that
eliminates the use for MergeNonPatterns.

R=adamk@chromium.org, littledan@chromium.org
BUG=
LOG=N

Review-Url: https://codereview.chromium.org/2275313002
Cr-Commit-Position: refs/heads/master@{#38934}

src/parsing/expression-classifier.h

@@ -285,7 +285,14 @@ class ExpressionClassifier {
     DCHECK_EQ(inner->reported_errors_, reported_errors_);
     DCHECK_EQ(inner->reported_errors_begin_, reported_errors_end_);
     DCHECK_EQ(inner->reported_errors_end_, reported_errors_->length());
-    if (merge_non_patterns) MergeNonPatterns(inner);
+    DCHECK_EQ(inner->non_patterns_to_rewrite_, non_patterns_to_rewrite_);
+    DCHECK_LE(non_pattern_begin_, inner->non_pattern_begin_);
+    DCHECK_LE(inner->non_pattern_begin_, non_patterns_to_rewrite_->length());
+    // Merge non-patterns from the inner classifier, or discard them.
+    if (merge_non_patterns)
+      inner->non_pattern_begin_ = non_patterns_to_rewrite_->length();
+    else
+      non_patterns_to_rewrite_->Rewind(inner->non_pattern_begin_);
     // Propagate errors from inner, but don't overwrite already recorded
     // errors.
     unsigned non_arrow_inner_invalid_productions =
@@ -376,11 +383,6 @@ class ExpressionClassifier {
     non_patterns_to_rewrite_->Rewind(non_pattern_begin_);
   }
 
-  V8_INLINE void MergeNonPatterns(ExpressionClassifier* inner) {
-    DCHECK_LE(non_pattern_begin_, inner->non_pattern_begin_);
-    inner->non_pattern_begin_ = inner->non_patterns_to_rewrite_->length();
-  }
-
  private:
   V8_INLINE const Error& reported_error(ErrorKind kind) const {
     if (invalid_productions_ & (1 << kind)) {

src/parsing/parser-base.h

@@ -2381,7 +2381,6 @@ ParserBase<Impl>::ParseAssignmentExpression(bool accept_IN,
   // form part of one.  Propagate speculative formal parameter error locations
   // (including those for binding patterns, since formal parameters can
   // themselves contain binding patterns).
-  // Do not merge pending non-pattern expressions yet!
   unsigned productions = ExpressionClassifier::AllProductions &
                          ~ExpressionClassifier::ArrowFormalParametersProduction;
 
@@ -2402,18 +2401,16 @@ ParserBase<Impl>::ParseAssignmentExpression(bool accept_IN,
                      ExpressionClassifier::TailCallExpressionProduction);
   }
 
-  classifier->Accumulate(&arrow_formals_classifier, productions, false);
-
   if (!Token::IsAssignmentOp(peek())) {
     // Parsed conditional expression only (no assignment).
-    // Now pending non-pattern expressions must be merged.
-    classifier->MergeNonPatterns(&arrow_formals_classifier);
+    // Pending non-pattern expressions must be merged.
+    classifier->Accumulate(&arrow_formals_classifier, productions);
     return expression;
+  } else {
+    // Pending non-pattern expressions must be discarded.
+    classifier->Accumulate(&arrow_formals_classifier, productions, false);
   }
 
-  // Now pending non-pattern expressions must be discarded.
-  arrow_formals_classifier.Discard();
-
   CheckNoTailCallExpressions(classifier, CHECK_OK);
 
   if (is_destructuring_assignment) {