Revert "Remove workaround for successors on end block from scheduler."

TBR=titzer@chromium.org

Review URL: https://codereview.chromium.org/705043002

Cr-Commit-Position: refs/heads/master@{#25194}
git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@25194 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/compiler/scheduler.cc

@@ -527,6 +527,7 @@ class SpecialRPONumberer : public ZoneObject {
         schedule_(schedule),
         order_(NULL),
         loops_(zone),
+        beyond_end_(NULL),
         backedges_(1, zone),
         stack_(zone),
         previous_block_count_(0) {}
@@ -534,9 +535,9 @@ class SpecialRPONumberer : public ZoneObject {
   // Computes the special reverse-post-order for the main control flow graph,
   // that is for the graph spanned between the schedule's start and end blocks.
   void ComputeSpecialRPO() {
-    DCHECK(schedule_->end()->SuccessorCount() == 0);
     DCHECK_EQ(NULL, order_);  // Main order does not exist yet.
-    ComputeAndInsertSpecialRPO(schedule_->start(), schedule_->end());
+    // TODO(mstarzinger): Should use Schedule::end() after tests are fixed.
+    ComputeAndInsertSpecialRPO(schedule_->start(), NULL);
   }
 
   // Computes the special reverse-post-order for a partial control flow graph,
@@ -569,9 +570,7 @@ class SpecialRPONumberer : public ZoneObject {
       l->block->set_rpo_number(number++);
       schedule_->rpo_order()->push_back(l->block);
     }
-    if (schedule_->end()->rpo_number() < 0) {
-      schedule_->end()->set_rpo_number(number);
-    }
+    BeyondEndSentinel()->set_rpo_number(number);
   }
 
   // Print and verify the special reverse-post-order.
@@ -656,6 +655,17 @@ class SpecialRPONumberer : public ZoneObject {
     return block->ao_number() >= 0;
   }
 
+  // TODO(mstarzinger): We only need this special sentinel because some tests
+  // use the schedule's end block in actual control flow (e.g. with end having
+  // successors). Once this has been cleaned up we can use the end block here.
+  BasicBlock* BeyondEndSentinel() {
+    if (beyond_end_ == NULL) {
+      BasicBlock::Id id = BasicBlock::Id::FromInt(-1);
+      beyond_end_ = new (schedule_->zone()) BasicBlock(schedule_->zone(), id);
+    }
+    return beyond_end_;
+  }
+
   // Compute special RPO for the control flow graph between {entry} and {end},
   // mutating any existing order so that the result is still valid.
   void ComputeAndInsertSpecialRPO(BasicBlock* entry, BasicBlock* end) {
@@ -838,7 +848,7 @@ class SpecialRPONumberer : public ZoneObject {
         ++loop_depth;
         current_loop = &loops_[GetLoopNumber(current)];
         BlockList* end = current_loop->end;
-        current->set_loop_end(end == NULL ? schedule_->end() : end->block);
+        current->set_loop_end(end == NULL ? BeyondEndSentinel() : end->block);
         current_header = current_loop->header;
         Trace("B%d is a loop header, increment loop depth to %d\n",
               current->id().ToInt(), loop_depth);
@@ -1008,6 +1018,7 @@ class SpecialRPONumberer : public ZoneObject {
   Schedule* schedule_;
   BlockList* order_;
   ZoneVector<LoopInfo> loops_;
+  BasicBlock* beyond_end_;
   ZoneList<Backedge> backedges_;
   ZoneVector<SpecialRPOStackFrame> stack_;
   size_t previous_block_count_;

test/cctest/compiler/test-scheduler.cc

@@ -200,13 +200,12 @@ TEST(RPOSelfLoop) {
 TEST(RPOEntryLoop) {
   HandleAndZoneScope scope;
   Schedule schedule(scope.main_zone());
-  BasicBlock* body = schedule.NewBasicBlock();
-  schedule.AddSuccessorForTesting(schedule.start(), body);
-  schedule.AddSuccessorForTesting(body, schedule.start());
+  schedule.AddSuccessorForTesting(schedule.start(), schedule.end());
+  schedule.AddSuccessorForTesting(schedule.end(), schedule.start());
   ZonePool zone_pool(scope.main_isolate());
   BasicBlockVector* order = Scheduler::ComputeSpecialRPO(&zone_pool, &schedule);
   CheckRPONumbers(order, 2, true);
-  BasicBlock* loop[] = {schedule.start(), body};
+  BasicBlock* loop[] = {schedule.start(), schedule.end()};
   CheckLoop(order, loop, 2);
 }
 
@@ -654,7 +653,7 @@ TEST(RPOLoopMultibackedge) {
   BasicBlock* A = schedule.start();
   BasicBlock* B = schedule.NewBasicBlock();
   BasicBlock* C = schedule.NewBasicBlock();
-  BasicBlock* D = schedule.NewBasicBlock();
+  BasicBlock* D = schedule.end();
   BasicBlock* E = schedule.NewBasicBlock();
 
   schedule.AddSuccessorForTesting(A, B);