[csa] Improve propagation of deferred block mark

Before this patch, loops in deferred code would defeat the propagation of the
deferred flag, since back edges would usually not come from deferred blocks,
thus stoping the forward propagation of the deferred flag at loop headers. This
patch ensures that back edges are ignored in the deferred propations, properly
placing loops dominated by deferred labels and the code that follows them into
deferred code.

R=epertoso@chromium.org
LOG=N

Review-Url: https://codereview.chromium.org/2606923002
Cr-Commit-Position: refs/heads/master@{#41976}

src/compiler/raw-machine-assembler.cc

@@ -51,12 +51,12 @@ Schedule* RawMachineAssembler::Export() {
     os << *schedule_;
   }
   schedule_->EnsureCFGWellFormedness();
+  Scheduler::ComputeSpecialRPO(zone(), schedule_);
   schedule_->PropagateDeferredMark();
   if (FLAG_trace_turbo_scheduler) {
     PrintF("--- EDGE SPLIT AND PROPAGATED DEFERRED SCHEDULE ------------\n");
     os << *schedule_;
   }
-  Scheduler::ComputeSpecialRPO(zone(), schedule_);
   // Invalidate RawMachineAssembler.
   Schedule* schedule = schedule_;
   schedule_ = nullptr;

src/compiler/schedule.cc

@@ -407,7 +407,7 @@ void Schedule::PropagateDeferredMark() {
       if (!block->deferred()) {
         bool deferred = block->PredecessorCount() > 0;
         for (auto pred : block->predecessors()) {
-          if (!pred->deferred()) {
+          if (!pred->deferred() && (pred->rpo_number() < block->rpo_number())) {
             deferred = false;
           }
         }