[crankshaft] Make infinite loop preserve control flow.

src/crankshaft/hydrogen.cc

Index: src/crankshaft/hydrogen.cc
diff --git a/src/crankshaft/hydrogen.cc b/src/crankshaft/hydrogen.cc
index 38a9fd0ad88425776d69b9485ac0ea852c81d91d..0de6dac78eca1008f326cebed6197a06cc7f68b4 100644
--- a/src/crankshaft/hydrogen.cc
+++ b/src/crankshaft/hydrogen.cc
@@ -5111,7 +5111,7 @@ void HOptimizedGraphBuilder::VisitDoWhileStatement(DoWhileStatement* stmt) {
   HBasicBlock* body_exit =
       JoinContinue(stmt, current_block(), break_info.continue_block());
   HBasicBlock* loop_successor = NULL;
-  if (body_exit != NULL && !stmt->cond()->ToBooleanIsTrue()) {
+  if (body_exit != NULL) {
     set_current_block(body_exit);
     loop_successor = graph()->CreateBasicBlock();
     if (stmt->cond()->ToBooleanIsFalse()) {
@@ -5153,19 +5153,17 @@ void HOptimizedGraphBuilder::VisitWhileStatement(WhileStatement* stmt) {
 
   // If the condition is constant true, do not generate a branch.
   HBasicBlock* loop_successor = NULL;
-  if (!stmt->cond()->ToBooleanIsTrue()) {
-    HBasicBlock* body_entry = graph()->CreateBasicBlock();
-    loop_successor = graph()->CreateBasicBlock();
-    CHECK_BAILOUT(VisitForControl(stmt->cond(), body_entry, loop_successor));
-    if (body_entry->HasPredecessor()) {
-      body_entry->SetJoinId(stmt->BodyId());
-      set_current_block(body_entry);
-    }
-    if (loop_successor->HasPredecessor()) {
-      loop_successor->SetJoinId(stmt->ExitId());
-    } else {
-      loop_successor = NULL;
-    }
+  HBasicBlock* body_entry = graph()->CreateBasicBlock();
+  loop_successor = graph()->CreateBasicBlock();
+  CHECK_BAILOUT(VisitForControl(stmt->cond(), body_entry, loop_successor));
+  if (body_entry->HasPredecessor()) {
+    body_entry->SetJoinId(stmt->BodyId());
+    set_current_block(body_entry);
+  }
+  if (loop_successor->HasPredecessor()) {
+    loop_successor->SetJoinId(stmt->ExitId());
+  } else {
+    loop_successor = NULL;
   }
 
   BreakAndContinueInfo break_info(stmt, scope());
@@ -5194,10 +5192,9 @@ void HOptimizedGraphBuilder::VisitForStatement(ForStatement* stmt) {
   DCHECK(current_block() != NULL);
   HBasicBlock* loop_entry = BuildLoopEntry(stmt);
 
-  HBasicBlock* loop_successor = NULL;
+  HBasicBlock* loop_successor = graph()->CreateBasicBlock();
+  HBasicBlock* body_entry = graph()->CreateBasicBlock();
   if (stmt->cond() != NULL) {
-    HBasicBlock* body_entry = graph()->CreateBasicBlock();
-    loop_successor = graph()->CreateBasicBlock();
     CHECK_BAILOUT(VisitForControl(stmt->cond(), body_entry, loop_successor));
     if (body_entry->HasPredecessor()) {
       body_entry->SetJoinId(stmt->BodyId());
@@ -5208,6 +5205,14 @@ void HOptimizedGraphBuilder::VisitForStatement(ForStatement* stmt) {
     } else {
       loop_successor = NULL;
     }
+  } else {
+    // Create dummy control flow so that variable liveness analysis
+    // produces teh correct result.
+    HControlInstruction* branch = New<HBranch>(graph()->GetConstantTrue());
+    branch->SetSuccessorAt(0, body_entry);
+    branch->SetSuccessorAt(1, loop_successor);
+    FinishCurrentBlock(branch);
+    set_current_block(body_entry);
   }
 
   BreakAndContinueInfo break_info(stmt, scope());