MachineScheduler: Remove ineffective heuristic; NFC

Currently all nodes get added to the NextSU list when they are released,
so any candidate must be in that list, making the heuristic ineffective.
Remove it for now, we can add it back later in a working fashion if
necessary.

llvm-svn: 282200

Author: MatzeB

llvm/include/llvm/CodeGen/MachineScheduler.h

@@ -589,10 +589,6 @@ class SchedBoundary {
   /// instruction.
   bool CheckPending;
 
-  // For heuristics, keep a list of the nodes that immediately depend on the
-  // most recently scheduled node.
-  SmallPtrSet<const SUnit*, 8> NextSUs;
-
   /// Number of cycles it takes to issue the instructions scheduled in this
   /// zone. It is defined as: scheduled-micro-ops / issue-width + stalls.
   /// See getStalls().
@@ -669,10 +665,6 @@ class SchedBoundary {
   /// Micro-ops issued in the current cycle
   unsigned getCurrMOps() const { return CurrMOps; }
 
-  /// Return true if the given SU is used by the most recently scheduled
-  /// instruction.
-  bool isNextSU(const SUnit *SU) const { return NextSUs.count(SU); }
-
   // The latency of dependence chains leading into this zone.
   unsigned getDependentLatency() const { return DependentLatency; }
 

llvm/lib/CodeGen/MachineScheduler.cpp

@@ -1793,7 +1793,6 @@ void SchedBoundary::reset() {
   Available.clear();
   Pending.clear();
   CheckPending = false;
-  NextSUs.clear();
   CurrCycle = 0;
   CurrMOps = 0;
   MinReadyCycle = UINT_MAX;
@@ -1994,9 +1993,6 @@ void SchedBoundary::releaseNode(SUnit *SU, unsigned ReadyCycle) {
     Pending.push(SU);
   else
     Available.push(SU);
-
-  // Record this node as an immediate dependent of the scheduled node.
-  NextSUs.insert(SU);
 }
 
 void SchedBoundary::releaseTopNode(SUnit *SU) {
@@ -2921,13 +2917,6 @@ void GenericScheduler::tryCandidate(SchedCandidate &Cand,
         !Rem.IsAcyclicLatencyLimited && tryLatency(TryCand, Cand, *Zone))
       return;
 
-    // Prefer immediate defs/users of the last scheduled instruction. This is a
-    // local pressure avoidance strategy that also makes the machine code
-    // readable.
-    if (tryGreater(Zone->isNextSU(TryCand.SU), Zone->isNextSU(Cand.SU),
-                   TryCand, Cand, NextDefUse))
-      return;
-
     // Fall through to original instruction order.
     if ((Zone->isTop() && TryCand.SU->NodeNum < Cand.SU->NodeNum)
         || (!Zone->isTop() && TryCand.SU->NodeNum > Cand.SU->NodeNum)) {