Optimize switch statements (second pass)

src/hydrogen.cc

Index: src/hydrogen.cc
diff --git a/src/hydrogen.cc b/src/hydrogen.cc
index 108d00c5a5c4e782b1f898bf9c930c0fbf3d2259..92b57c46aa8e578941ce86ca05b1081aa21d87a9 100644
--- a/src/hydrogen.cc
+++ b/src/hydrogen.cc
@@ -2742,8 +2742,25 @@ void HGraphBuilder::VisitSwitchStatement(SwitchStatement* stmt) {
   HUnaryControlInstruction* string_check = NULL;
   HBasicBlock* not_string_block = NULL;
 
+  int iterations = clause_count;
+
   // Test switch's tag value if all clauses are string literals
   if (switch_type == STRING_SWITCH) {
+    // Bailout if we seen string(non-symbol) comparisons here
+    for (int i = 0; i < clause_count; ++i) {
+      CaseClause* clause = clauses->at(i);
+      if (clause->is_default()) continue;
+
+      clause->RecordTypeFeedback(oracle());
+
+      if (clause->IsStringCompare()) {
+        return Bailout("SwitchStatement: no symbol comparisons expected");
+      }
+    }
+
+    // We'll generate two passes of checks
+    iterations = iterations * 2;
+
     string_check = new(zone()) HIsStringAndBranch(tag_value);
     first_test_block = graph()->CreateBasicBlock();
     not_string_block = graph()->CreateBasicBlock();
@@ -2756,8 +2773,8 @@ void HGraphBuilder::VisitSwitchStatement(SwitchStatement* stmt) {
   }
 
   // 2. Build all the tests, with dangling true branches
-  for (int i = 0; i < clause_count; ++i) {
-    CaseClause* clause = clauses->at(i);
+  for (int i = 0; i < iterations; ++i) {
+    CaseClause* clause = clauses->at(i % clause_count);
     if (clause->is_default()) continue;
 
     if (switch_type == SMI_SWITCH) {
@@ -2789,9 +2806,13 @@ void HGraphBuilder::VisitSwitchStatement(SwitchStatement* stmt) {
       compare_->SetInputRepresentation(Representation::Integer32());
       compare = compare_;
     } else {
-      compare = new(zone()) HStringCompareAndBranch(context, tag_value,
-                                                     label_value,
-                                                     Token::EQ_STRICT);
+      if (i < clause_count) {
+        compare = new(zone()) HCompareObjectEqAndBranch(tag_value, label_value);
+      } else {
+        compare = new(zone()) HStringCompareAndBranch(context, tag_value,
+                                                       label_value,
+                                                       Token::EQ_STRICT);
+      }
     }
 
     compare->SetSuccessorAt(0, body_block);
@@ -2813,11 +2834,18 @@ void HGraphBuilder::VisitSwitchStatement(SwitchStatement* stmt) {
   // translating the clause bodies.
   HBasicBlock* curr_test_block = first_test_block;
   HBasicBlock* fall_through_block = NULL;
+  HBasicBlock* fall_through_block_left = NULL;
 
   BreakAndContinueInfo break_info(stmt);
   { BreakAndContinueScope push(&break_info, this);
-    for (int i = 0; i < clause_count; ++i) {
-      CaseClause* clause = clauses->at(i);
+    for (int i = 0; i < iterations; ++i) {
+      // Create shadow last block for second pass
+      if (i == clause_count) {
+        fall_through_block_left = fall_through_block;
+        fall_through_block = NULL;
+      }
+
+      CaseClause* clause = clauses->at(i % clause_count);
 
       // Identify the block where normal (non-fall-through) control flow
       // goes to.
@@ -2861,6 +2889,10 @@ void HGraphBuilder::VisitSwitchStatement(SwitchStatement* stmt) {
     }
   }
 
+  // Join tails of parallel branches
+  fall_through_block = CreateJoin(fall_through_block, fall_through_block_left,
+                                  stmt->ExitId());
+
   // Create an up-to-3-way join.  Use the break block if it exists since
   // it's already a join block.
   HBasicBlock* break_block = break_info.break_block();