[hydrogen] optimize switch with string clauses

src/hydrogen.cc

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 2672 matching lines @@
   int clause_count = clauses->length();
   if (clause_count > kCaseClauseLimit) {
     return Bailout("SwitchStatement: too many clauses");
   }
 
   CHECK_ALIVE(VisitForValue(stmt->tag()));
   AddSimulate(stmt->EntryId());
   HValue* tag_value = Pop();
   HBasicBlock* first_test_block = current_block();
 
-  // 1. Build all the tests, with dangling true branches.  Unconditionally
-  // deoptimize if we encounter a non-smi comparison.
+  SwitchType switch_type = UNKNOWN_SWITCH;
+
+  // 1. Extract clause type
   for (int i = 0; i < clause_count; ++i) {
     CaseClause* clause = clauses->at(i);
     if (clause->is_default()) continue;
-    if (!clause->label()->IsSmiLiteral()) {
-      return Bailout("SwitchStatement: non-literal switch label");
+
+    if (switch_type == UNKNOWN_SWITCH) {
+      if (clause->label()->IsSmiLiteral()) {
+        switch_type = SMI_SWITCH;
+      } else if (clause->label()->IsStringLiteral()) {
+        switch_type = STRING_SWITCH;
+      } else {
+        return Bailout("SwitchStatement: non-literal switch label");
+      }
+    } else if ((switch_type == STRING_SWITCH &&
+                !clause->label()->IsStringLiteral()) ||
+               (switch_type == SMI_SWITCH &&
+                !clause->label()->IsSmiLiteral())) {
+      return Bailout("SwitchStatemnt: mixed label types are not supported");
+    }
+  }
+
+  // Test switch's tag value if all clauses are string literals
+  if (switch_type == STRING_SWITCH) {
+    AddInstruction(HCheckInstanceType::NewIsSymbol(tag_value));
+    AddInstruction(new(zone()) HCheckNonSmi(tag_value));

[Vyacheslav Egorov (Chromium), 2011/10/24 12:27:29]

Checking that tag_value is non-smi after is-symbol already segfaulted is not
very helpful. 

Usually you want to check for something before you segfault.

+  }
+
+  // 2. Build all the tests, with dangling true branches
+  for (int i = 0; i < clause_count; ++i) {
+    CaseClause* clause = clauses->at(i);
+    if (clause->is_default()) continue;
+
+    clause->RecordTypeFeedback(oracle());
+
+    // Generate a compare and branch.
+    CHECK_ALIVE(VisitForValue(clause->label()));
+    HValue* label_value = Pop();
+
+    HBasicBlock* next_test_block = graph()->CreateBasicBlock();
+    HBasicBlock* body_block = graph()->CreateBasicBlock();
+
+    HControlInstruction* compare;
+
+    if (switch_type == SMI_SWITCH) {
+      if (!clause->IsSmiCompare()) {
+        // Finish with deoptimize and add uses of enviroment values to
+        // account for invisible uses.
+        current_block()->FinishExitWithDeoptimization(HDeoptimize::kUseAll);
+        set_current_block(NULL);
+        break;
+      }
+
+      HCompareIDAndBranch* compare_ =
+          new(zone()) HCompareIDAndBranch(tag_value,
+                                          label_value,
+                                          Token::EQ_STRICT);
+      compare_->SetInputRepresentation(Representation::Integer32());
+      compare = compare_;
+    } else {
+      compare = new(zone()) HCompareObjectEqAndBranch(tag_value, label_value);
     }
 
-    // Unconditionally deoptimize on the first non-smi compare.
-    clause->RecordTypeFeedback(oracle());
-    if (!clause->IsSmiCompare()) {
-      // Finish with deoptimize and add uses of enviroment values to
-      // account for invisible uses.
-      current_block()->FinishExitWithDeoptimization(HDeoptimize::kUseAll);
-      set_current_block(NULL);
-      break;
-    }
-
-    // Otherwise generate a compare and branch.
-    CHECK_ALIVE(VisitForValue(clause->label()));
-    HValue* label_value = Pop();
-    HCompareIDAndBranch* compare =
-        new(zone()) HCompareIDAndBranch(tag_value,
-                                        label_value,
-                                        Token::EQ_STRICT);
-    compare->SetInputRepresentation(Representation::Integer32());
-    HBasicBlock* body_block = graph()->CreateBasicBlock();
-    HBasicBlock* next_test_block = graph()->CreateBasicBlock();
     compare->SetSuccessorAt(0, body_block);
     compare->SetSuccessorAt(1, next_test_block);
     current_block()->Finish(compare);
+
     set_current_block(next_test_block);
   }
 
   // Save the current block to use for the default or to join with the
   // exit.  This block is NULL if we deoptimized.
   HBasicBlock* last_block = current_block();
 
-  // 2. Loop over the clauses and the linked list of tests in lockstep,
+  // 3. Loop over the clauses and the linked list of tests in lockstep,
   // translating the clause bodies.
   HBasicBlock* curr_test_block = first_test_block;
   HBasicBlock* fall_through_block = NULL;
   BreakAndContinueInfo break_info(stmt);
   { BreakAndContinueScope push(&break_info, this);
     for (int i = 0; i < clause_count; ++i) {
       CaseClause* clause = clauses->at(i);
 
       // Identify the block where normal (non-fall-through) control flow
       // goes to.
@@ skipping 4270 matching lines @@
     }
   }
 
 #ifdef DEBUG
   if (graph_ != NULL) graph_->Verify(false);  // No full verify.
   if (allocator_ != NULL) allocator_->Verify();
 #endif
 }
 
 } }  // namespace v8::internal