[llvm] r328554 - [Pipeliner] Several node-ordering fixes

[Krzysztof Parzyszek via llvm-commits]

Author: kparzysz
Date: Mon Mar 26 10:07:41 2018
New Revision: 328554

URL: http://llvm.org/viewvc/llvm-project?rev=328554&view=rev
Log:
[Pipeliner] Several node-ordering fixes

First, we change the heuristic that is used to ignore the recurrent
node-sets in the node ordering. In certain cases it's not important
to focus on the recurrent node-sets.  Instead, the algorithm begins
by considering all the instructions in the node ordering step.

Second, a minor change to the bottom up traversal, which needs to
consider loop carried dependences (modeled as anti dependences).
Previously, these instructions were skipped, which caused problems
because the instruction ends up having both predecessors and
sucessors in the schedule.

Third, consider anti-dependences as a tie breaker when choosing
between instructions in the node ordering. We want to make sure
that the source of the anti-dependence does not end up with both
predecesssors and sucessors in the final node ordering.

Patch by Brendon Cahoon.

Modified:
    llvm/trunk/lib/CodeGen/MachinePipeliner.cpp

Modified: llvm/trunk/lib/CodeGen/MachinePipeliner.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/MachinePipeliner.cpp?rev=328554&r1=328553&r2=328554&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/MachinePipeliner.cpp (original)
+++ llvm/trunk/lib/CodeGen/MachinePipeliner.cpp Mon Mar 26 10:07:41 2018
@@ -322,7 +322,7 @@ public:
   int getMOV(SUnit *Node) { return getALAP(Node) - getASAP(Node); }
 
   /// The depth, in the dependence graph, for a node.
-  int getDepth(SUnit *Node) { return Node->getDepth(); }
+  unsigned getDepth(SUnit *Node) { return Node->getDepth(); }
 
   /// The maximum unweighted length of a path from an arbitrary node to the
   /// given node in which each edge has latency 0
@@ -331,7 +331,7 @@ public:
   }
 
   /// The height, in the dependence graph, for a node.
-  int getHeight(SUnit *Node) { return Node->getHeight(); }
+  unsigned getHeight(SUnit *Node) { return Node->getHeight(); }
 
   /// The maximum unweighted length of a path from the given node to an
   /// arbitrary node in which each edge has latency 0
@@ -460,7 +460,7 @@ class NodeSet {
   bool HasRecurrence = false;
   unsigned RecMII = 0;
   int MaxMOV = 0;
-  int MaxDepth = 0;
+  unsigned MaxDepth = 0;
   unsigned Colocate = 0;
   SUnit *ExceedPressure = nullptr;
   unsigned Latency = 0;
@@ -517,6 +517,8 @@ public:
 
   unsigned getLatency() { return Latency; }
 
+  unsigned getMaxDepth() { return MaxDepth; }
+
   void clear() {
     Nodes.clear();
     RecMII = 0;
@@ -1917,25 +1919,23 @@ void SwingSchedulerDAG::colocateNodeSets
 
 /// Check if the existing node-sets are profitable. If not, then ignore the
 /// recurrent node-sets, and attempt to schedule all nodes together. This is
-/// a heuristic. If the MII is large and there is a non-recurrent node with
-/// a large depth compared to the MII, then it's best to try and schedule
-/// all instruction together instead of starting with the recurrent node-sets.
+/// a heuristic. If the MII is large and all the recurrent node-sets are small,
+/// then it's best to try to schedule all instructions together instead of
+/// starting with the recurrent node-sets.
 void SwingSchedulerDAG::checkNodeSets(NodeSetType &NodeSets) {
   // Look for loops with a large MII.
-  if (MII <= 20)
+  if (MII < 17)
     return;
   // Check if the node-set contains only a simple add recurrence.
-  for (auto &NS : NodeSets)
-    if (NS.size() > 2)
+  for (auto &NS : NodeSets) {
+    if (NS.getRecMII() > 2)
       return;
-  // If the depth of any instruction is significantly larger than the MII, then
-  // ignore the recurrent node-sets and treat all instructions equally.
-  for (auto &SU : SUnits)
-    if (SU.getDepth() > MII * 1.5) {
-      NodeSets.clear();
-      DEBUG(dbgs() << "Clear recurrence node-sets\n");
+    if (NS.getMaxDepth() > MII)
       return;
-    }
+  }
+  NodeSets.clear();
+  DEBUG(dbgs() << "Clear recurrence node-sets\n");
+  return;
 }
 
 /// Add the nodes that do not belong to a recurrence set into groups
@@ -2193,8 +2193,6 @@ void SwingSchedulerDAG::computeNodeOrder
               continue;
             if (NodeOrder.count(I.getSUnit()) != 0)
               continue;
-            if (I.getKind() == SDep::Anti)
-              continue;
             R.insert(I.getSUnit());
           }
           // Back-edges are predecessors with an anti-dependence.