[turbofan] Instruction scheduler: keep ready nodes list sorted by latency.

This significantly speed-up the instruction scheduler when the ready list
contains a large number of instruction.

R=jarin@chromium.org, bmeurer@chromium.org

Review-Url: https://codereview.chromium.org/2281523002
Cr-Commit-Position: refs/heads/master@{#38919}

src/compiler/instruction-scheduler.cc

@@ -11,11 +11,16 @@ namespace v8 {
 namespace internal {
 namespace compiler {
 
-// Compare the two nodes and return true if node1 is a better candidate than
-// node2 (i.e. node1 should be scheduled before node2).
-bool InstructionScheduler::CriticalPathFirstQueue::CompareNodes(
-    ScheduleGraphNode *node1, ScheduleGraphNode *node2) const {
-  return node1->total_latency() > node2->total_latency();
+void InstructionScheduler::SchedulingQueueBase::AddNode(
+    ScheduleGraphNode* node) {
+  // We keep the ready list sorted by total latency so that we can quickly find
+  // the next best candidate to schedule.
+  auto it = nodes_.begin();
+  while ((it != nodes_.end()) &&
+         ((*it)->total_latency() > node->total_latency())) {
+    ++it;
+  }
+  nodes_.insert(it, node);
 }
 
 
@@ -24,12 +29,10 @@ InstructionScheduler::CriticalPathFirstQueue::PopBestCandidate(int cycle) {
   DCHECK(!IsEmpty());
   auto candidate = nodes_.end();
   for (auto iterator = nodes_.begin(); iterator != nodes_.end(); ++iterator) {
-    // We only consider instructions that have all their operands ready and
-    // we try to schedule the critical path first.
+    // We only consider instructions that have all their operands ready.
     if (cycle >= (*iterator)->start_cycle()) {
-      if ((candidate == nodes_.end()) || CompareNodes(*iterator, *candidate)) {
-        candidate = iterator;
-      }
+      candidate = iterator;
+      break;
     }
   }
 

src/compiler/instruction-scheduler.h

@@ -101,9 +101,7 @@ class InstructionScheduler final : public ZoneObject {
         nodes_(scheduler->zone()) {
     }
 
-    void AddNode(ScheduleGraphNode* node) {
-      nodes_.push_back(node);
-    }
+    void AddNode(ScheduleGraphNode* node);
 
     bool IsEmpty() const {
       return nodes_.empty();
@@ -125,11 +123,6 @@ class InstructionScheduler final : public ZoneObject {
     // Look for the best candidate to schedule, remove it from the queue and
     // return it.
     ScheduleGraphNode* PopBestCandidate(int cycle);
-
-   private:
-    // Compare the two nodes and return true if node1 is a better candidate than
-    // node2 (i.e. node1 should be scheduled before node2).
-    bool CompareNodes(ScheduleGraphNode *node1, ScheduleGraphNode *node2) const;
   };
 
   // A queue which pop a random node from the queue to perform stress tests on