Enable optimization of functions with generic switches.

src/hydrogen.cc

 // Copyright 2013 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 4123 matching lines @@
 void HOptimizedGraphBuilder::VisitSwitchStatement(SwitchStatement* stmt) {
   ASSERT(!HasStackOverflow());
   ASSERT(current_block() != NULL);
   ASSERT(current_block()->HasPredecessor());
 
   // We only optimize switch statements with smi-literal smi comparisons,
   // with a bounded number of clauses.
   const int kCaseClauseLimit = 128;
   ZoneList<CaseClause*>* clauses = stmt->cases();
   int clause_count = clauses->length();
+  ZoneList<HBasicBlock*> body_blocks(clause_count, zone());
   if (clause_count > kCaseClauseLimit) {
     return Bailout(kSwitchStatementTooManyClauses);
   }
 
   ASSERT(stmt->switch_type() != SwitchStatement::UNKNOWN_SWITCH);
-  if (stmt->switch_type() == SwitchStatement::GENERIC_SWITCH) {
-    return Bailout(kSwitchStatementMixedOrNonLiteralSwitchLabels);
-  }
 
   CHECK_ALIVE(VisitForValue(stmt->tag()));
   Add<HSimulate>(stmt->EntryId());
-  HValue* tag_value = Pop();
-  HBasicBlock* first_test_block = current_block();
+  HValue* tag_value = Top();
 
   HUnaryControlInstruction* string_check = NULL;
   HBasicBlock* not_string_block = NULL;
 
   // Test switch's tag value if all clauses are string literals
   if (stmt->switch_type() == SwitchStatement::STRING_SWITCH) {
-    first_test_block = graph()->CreateBasicBlock();
+    HBasicBlock* first_test_block = graph()->CreateBasicBlock();
     not_string_block = graph()->CreateBasicBlock();
     string_check = New<HIsStringAndBranch>(
         tag_value, first_test_block, not_string_block);
     FinishCurrentBlock(string_check);
 
+    set_current_block(not_string_block);
+    Drop(1);  // tag_value
+
     set_current_block(first_test_block);
   }
 
   // 1. Build all the tests, with dangling true branches
   BailoutId default_id = BailoutId::None();
   for (int i = 0; i < clause_count; ++i) {

[titzer, 2013/12/10 14:27:09]

It seems like this loop can be rewritten to go over the clauses once, generating
the compares and the body blocks in one pass. If so, then we can get rid of this
body_blocks array altogether.

     CaseClause* clause = clauses->at(i);
     if (clause->is_default()) {
-      default_id = clause->EntryId();
+      body_blocks.Add(NULL, zone());
+      if (default_id.IsNone()) default_id = clause->EntryId();
       continue;
     }
 
     // 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 (stmt->switch_type() == SwitchStatement::SMI_SWITCH) {
       if (!clause->compare_type()->Is(Type::Smi())) {
         Add<HDeoptimize>("Non-smi switch type", Deoptimizer::SOFT);
       }
 
       HCompareNumericAndBranch* compare_ =
           New<HCompareNumericAndBranch>(tag_value,
                                         label_value,
                                         Token::EQ_STRICT);
       compare_->set_observed_input_representation(
           Representation::Smi(), Representation::Smi());
       compare = compare_;
-    } else {
+    } else if (stmt->switch_type() == SwitchStatement::STRING_SWITCH) {
       compare = New<HStringCompareAndBranch>(tag_value,
                                              label_value,
                                              Token::EQ_STRICT);
+    } else {
+      HValue* test = Add<HCompareGeneric>(tag_value,
+                                          label_value,
+                                          Token::EQ_STRICT);
+      if (test->HasObservableSideEffects()) {
+        Push(test);
+        Add<HSimulate>(clause->id(), REMOVABLE_SIMULATE);
+        Drop(1);
+      }
+      compare = New<HBranch>(test);
     }
 
+    HBasicBlock* next_test_block = graph()->CreateBasicBlock();
+    HBasicBlock* body_block = graph()->CreateBasicBlock();
+    body_blocks.Add(body_block, zone());
     compare->SetSuccessorAt(0, body_block);
     compare->SetSuccessorAt(1, next_test_block);
     FinishCurrentBlock(compare);
 
+    set_current_block(body_block);
+    Drop(1);  // tag_value
+
     set_current_block(next_test_block);
   }
 
   // Save the current block to use for the default or to join with the
   // exit.
   HBasicBlock* last_block = current_block();
+  Drop(1);  // tag_value
 
   if (not_string_block != NULL) {
     BailoutId join_id = !default_id.IsNone() ? default_id : stmt->ExitId();
     last_block = CreateJoin(last_block, not_string_block, join_id);
   }
 
   // 2. 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.
       HBasicBlock* normal_block = NULL;
       if (clause->is_default()) {
-        if (last_block != NULL) {
-          normal_block = last_block;
-          last_block = NULL;  // Cleared to indicate we've handled it.
-        }
+        if (last_block == NULL) continue;
+        normal_block = last_block;
+        last_block = NULL;  // Cleared to indicate we've handled it.
       } else {
-        // If the current test block is deoptimizing due to an unhandled clause
-        // of the switch, the test instruction is in the next block since the
-        // deopt must end the current block.
-        if (curr_test_block->IsDeoptimizing()) {
-          ASSERT(curr_test_block->end()->SecondSuccessor() == NULL);
-          curr_test_block = curr_test_block->end()->FirstSuccessor();
-        }
-        normal_block = curr_test_block->end()->FirstSuccessor();
-        curr_test_block = curr_test_block->end()->SecondSuccessor();
+        normal_block = body_blocks[i];
       }
 
-      // Identify a block to emit the body into.
-      if (normal_block == NULL) {
-        if (fall_through_block == NULL) {
-          // (a) Unreachable.
-          if (clause->is_default()) {
-            continue;  // Might still be reachable clause bodies.
-          } else {
-            break;
-          }
-        } else {
-          // (b) Reachable only as fall through.
-          set_current_block(fall_through_block);
-        }
-      } else if (fall_through_block == NULL) {
-        // (c) Reachable only normally.
+      if (fall_through_block == NULL) {
         set_current_block(normal_block);
       } else {
-        // (d) Reachable both ways.
         HBasicBlock* join = CreateJoin(fall_through_block,
                                        normal_block,
                                        clause->EntryId());
         set_current_block(join);
       }
 
       CHECK_BAILOUT(VisitStatements(clause->statements()));
       fall_through_block = current_block();
     }
   }
@@ skipping 6529 matching lines @@
   if (ShouldProduceTraceOutput()) {
     isolate()->GetHTracer()->TraceHydrogen(name(), graph_);
   }
 
 #ifdef DEBUG
   graph_->Verify(false);  // No full verify.
 #endif
 }
 
 } }  // namespace v8::internal