From: Jakob Stoklund Olesen <stoklund@2pi.dk>
Date: Wed, 23 Feb 2011 00:29:52 +0000 (+0000)
Subject: Be more aggressive about evicting interference.
X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=98c8141b6d8fcbb9bd258ebcdd4171f55c5a8e9d;p=oota-llvm.git

Be more aggressive about evicting interference.

Use interval sizes instead of spill weights to determine if it is legal to evict
interference. A smaller interval can evict interference if all interfering live
ranges are larger.

Allow multiple interferences to be evicted as along as they are all larger than
the live range being allocated.

Spill weights are still used to select the preferred eviction candidate.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@126276 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/CodeGen/RegAllocGreedy.cpp b/lib/CodeGen/RegAllocGreedy.cpp
index e1b9f3702f4..0146a276216 100644
--- a/lib/CodeGen/RegAllocGreedy.cpp
+++ b/lib/CodeGen/RegAllocGreedy.cpp
@@ -119,9 +119,12 @@ private:
   SlotIndex getPrevMappedIndex(const MachineInstr*);
   void calcPrevSlots();
   unsigned nextSplitPoint(unsigned);
+  bool canEvictInterference(LiveInterval&, unsigned, unsigned, float&);
 
-  unsigned tryReassignOrEvict(LiveInterval&, AllocationOrder&,
+  unsigned tryReassign(LiveInterval&, AllocationOrder&,
                               SmallVectorImpl<LiveInterval*>&);
+  unsigned tryEvict(LiveInterval&, AllocationOrder&,
+                    SmallVectorImpl<LiveInterval*>&);
   unsigned tryRegionSplit(LiveInterval&, AllocationOrder&,
                           SmallVectorImpl<LiveInterval*>&);
   unsigned tryLocalSplit(LiveInterval&, AllocationOrder&,
@@ -283,21 +286,14 @@ bool RAGreedy::reassignVReg(LiveInterval &InterferingVReg,
   return false;
 }
 
-/// tryReassignOrEvict - Try to reassign a single interferences to a different
-/// physreg, or evict a single interference with a lower spill weight.
+/// tryReassign - Try to reassign a single interference to a different physreg.
 /// @param  VirtReg Currently unassigned virtual register.
 /// @param  Order   Physregs to try.
 /// @return         Physreg to assign VirtReg, or 0.
-unsigned RAGreedy::tryReassignOrEvict(LiveInterval &VirtReg,
-                                      AllocationOrder &Order,
-                                      SmallVectorImpl<LiveInterval*> &NewVRegs){
+unsigned RAGreedy::tryReassign(LiveInterval &VirtReg, AllocationOrder &Order,
+                               SmallVectorImpl<LiveInterval*> &NewVRegs){
   NamedRegionTimer T("Reassign", TimerGroupName, TimePassesIsEnabled);
 
-  // Keep track of the lightest single interference seen so far.
-  float BestWeight = VirtReg.weight;
-  LiveInterval *BestVirt = 0;
-  unsigned BestPhys = 0;
-
   Order.rewind();
   while (unsigned PhysReg = Order.next()) {
     LiveInterval *InterferingVReg = getSingleInterference(VirtReg, PhysReg);
@@ -307,25 +303,89 @@ unsigned RAGreedy::tryReassignOrEvict(LiveInterval &VirtReg,
       continue;
     if (reassignVReg(*InterferingVReg, PhysReg))
       return PhysReg;
+  }
+  return 0;
+}
+
+
+//===----------------------------------------------------------------------===//
+//                         Interference eviction
+//===----------------------------------------------------------------------===//
 
-    // Cannot reassign, is this an eviction candidate?
-    if (InterferingVReg->weight < BestWeight) {
-      BestVirt = InterferingVReg;
-      BestPhys = PhysReg;
-      BestWeight = InterferingVReg->weight;
+/// canEvict - Return true if all interferences between VirtReg and PhysReg can
+/// be evicted. Set maxWeight to the maximal spill weight of an interference.
+bool RAGreedy::canEvictInterference(LiveInterval &VirtReg, unsigned PhysReg,
+                                    unsigned Size, float &MaxWeight) {
+  float Weight = 0;
+  for (const unsigned *AliasI = TRI->getOverlaps(PhysReg); *AliasI; ++AliasI) {
+    LiveIntervalUnion::Query &Q = query(VirtReg, *AliasI);
+    // If there is 10 or more interferences, chances are one is smaller.
+    if (Q.collectInterferingVRegs(10) >= 10)
+      return false;
+
+    // CHeck if any interfering live range is shorter than VirtReg.
+    for (unsigned i = 0, e = Q.interferingVRegs().size(); i != e; ++i) {
+      LiveInterval *Intf = Q.interferingVRegs()[i];
+      if (TargetRegisterInfo::isPhysicalRegister(Intf->reg))
+        return false;
+      if (Intf->getSize() <= Size)
+        return false;
+      Weight = std::max(Weight, Intf->weight);
     }
   }
+  MaxWeight = Weight;
+  return true;
+}
+
+/// tryEvict - Try to evict all interferences for a physreg.
+/// @param  VirtReg Currently unassigned virtual register.
+/// @param  Order   Physregs to try.
+/// @return         Physreg to assign VirtReg, or 0.
+unsigned RAGreedy::tryEvict(LiveInterval &VirtReg,
+                            AllocationOrder &Order,
+                            SmallVectorImpl<LiveInterval*> &NewVRegs){
+  NamedRegionTimer T("Evict", TimerGroupName, TimePassesIsEnabled);
+
+  // We can only evict interference if all interfering registers are virtual and
+  // longer than VirtReg.
+  const unsigned Size = VirtReg.getSize();
 
-  // Nothing reassigned, can we evict a lighter single interference?
-  if (BestVirt) {
-    DEBUG(dbgs() << "evicting lighter " << *BestVirt << '\n');
-    unassign(*BestVirt, VRM->getPhys(BestVirt->reg));
-    ++NumEvicted;
-    NewVRegs.push_back(BestVirt);
-    return BestPhys;
+  // Keep track of the lightest single interference seen so far.
+  float BestWeight = 0;
+  unsigned BestPhys = 0;
+
+  Order.rewind();
+  while (unsigned PhysReg = Order.next()) {
+    float Weight = 0;
+    if (!canEvictInterference(VirtReg, PhysReg, Size, Weight))
+      continue;
+
+    // This is an eviction candidate.
+    DEBUG(dbgs() << "max " << PrintReg(PhysReg, TRI) << " interference = "
+                 << Weight << '\n');
+    if (BestPhys && Weight >= BestWeight)
+      continue;
+
+    // Best so far.
+    BestPhys = PhysReg;
+    BestWeight = Weight;
   }
 
-  return 0;
+  if (!BestPhys)
+    return 0;
+
+  DEBUG(dbgs() << "evicting " << PrintReg(BestPhys, TRI) << " interference\n");
+  for (const unsigned *AliasI = TRI->getOverlaps(BestPhys); *AliasI; ++AliasI) {
+    LiveIntervalUnion::Query &Q = query(VirtReg, *AliasI);
+    assert(Q.seenAllInterferences() && "Didn't check all interfererences.");
+    for (unsigned i = 0, e = Q.interferingVRegs().size(); i != e; ++i) {
+      LiveInterval *Intf = Q.interferingVRegs()[i];
+      unassign(*Intf, VRM->getPhys(Intf->reg));
+      ++NumEvicted;
+      NewVRegs.push_back(Intf);
+    }
+  }
+  return BestPhys;
 }
 
 
@@ -1237,8 +1297,10 @@ unsigned RAGreedy::selectOrSplit(LiveInterval &VirtReg,
       return PhysReg;
   }
 
-  // Try to reassign interferences.
-  if (unsigned PhysReg = tryReassignOrEvict(VirtReg, Order, NewVRegs))
+  if (unsigned PhysReg = tryReassign(VirtReg, Order, NewVRegs))
+    return PhysReg;
+
+  if (unsigned PhysReg = tryEvict(VirtReg, Order, NewVRegs))
     return PhysReg;
 
   assert(NewVRegs.empty() && "Cannot append to existing NewVRegs");