[crankshaft] Make infinite loop preserve control flow.

src/crankshaft/hydrogen.cc

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/crankshaft/hydrogen.h"
 
 #include <sstream>
 
 #include "src/allocation-site-scopes.h"
 #include "src/ast/ast-numbering.h"
@@ skipping 5093 matching lines @@
   HBasicBlock* loop_entry = BuildLoopEntry(stmt);
 
   BreakAndContinueInfo break_info(stmt, scope());
   {
     BreakAndContinueScope push(&break_info, this);
     CHECK_BAILOUT(VisitLoopBody(stmt, loop_entry));
   }
   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()) {
       loop_entry->loop_information()->stack_check()->Eliminate();
       Goto(loop_successor);
       body_exit = NULL;
     } else {
       // The block for a true condition, the actual predecessor block of the
       // back edge.
       body_exit = graph()->CreateBasicBlock();
@@ skipping 21 matching lines @@
 
 void HOptimizedGraphBuilder::VisitWhileStatement(WhileStatement* stmt) {
   DCHECK(!HasStackOverflow());
   DCHECK(current_block() != NULL);
   DCHECK(current_block()->HasPredecessor());
   DCHECK(current_block() != NULL);
   HBasicBlock* loop_entry = BuildLoopEntry(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());
   if (current_block() != NULL) {
     BreakAndContinueScope push(&break_info, this);
     CHECK_BAILOUT(VisitLoopBody(stmt, loop_entry));
   }
   HBasicBlock* body_exit =
       JoinContinue(stmt, current_block(), break_info.continue_block());
   HBasicBlock* loop_exit = CreateLoop(stmt,
                                       loop_entry,
                                       body_exit,
                                       loop_successor,
                                       break_info.break_block());
   set_current_block(loop_exit);
 }
 
 
 void HOptimizedGraphBuilder::VisitForStatement(ForStatement* stmt) {
   DCHECK(!HasStackOverflow());
   DCHECK(current_block() != NULL);
   DCHECK(current_block()->HasPredecessor());
   if (stmt->init() != NULL) {
     CHECK_ALIVE(Visit(stmt->init()));
   }
   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());
       set_current_block(body_entry);
     }
     if (loop_successor->HasPredecessor()) {
       loop_successor->SetJoinId(stmt->ExitId());
     } 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());
   if (current_block() != NULL) {
     BreakAndContinueScope push(&break_info, this);
     CHECK_BAILOUT(VisitLoopBody(stmt, loop_entry));
   }
   HBasicBlock* body_exit =
       JoinContinue(stmt, current_block(), break_info.continue_block());
 
@@ skipping 8349 matching lines @@
     isolate()->GetHTracer()->TraceHydrogen(name(), graph_);
   }
 
 #ifdef DEBUG
   graph_->Verify(false);  // No full verify.
 #endif
 }
 
 }  // namespace internal
 }  // namespace v8