Change the RAGreedy register assignment order so large live ranges are allocated first.

This is based on the observation that long live ranges are more difficult to
allocate, so there is a better chance of solving the puzzle by handling the big
pieces first. The allocator will evict and split long alive ranges when they get
in the way.

RABasic is still using spill weights for its priority queue, so the interface to
the queue has been virtualized.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@126259 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 37 insertions, 23 deletions

diff --git a/lib/CodeGen/RegAllocBasic.cpp b/lib/CodeGen/RegAllocBasic.cpp
index 045c8db9da..6923908a32 100644
--- a/lib/CodeGen/RegAllocBasic.cpp
+++ b/lib/CodeGen/RegAllocBasic.cpp
@@ -45,6 +45,7 @@
 #include "llvm/Support/Timer.h"
 
 #include <cstdlib>
+#include <queue>
 
 using namespace llvm;
 
@@ -65,6 +66,14 @@ const char *RegAllocBase::TimerGroupName = "Register Allocation";
 bool RegAllocBase::VerifyEnabled = false;
 
 namespace {
+  struct CompSpillWeight {
+    bool operator()(LiveInterval *A, LiveInterval *B) const {
+      return A->weight < B->weight;
+    }
+  };
+}
+
+namespace {
 /// RABasic provides a minimal implementation of the basic register allocation
 /// algorithm. It prioritizes live virtual registers by spill weight and spills
 /// whenever a register is unavailable. This is not practical in production but
@@ -82,7 +91,8 @@ class RABasic : public MachineFunctionPass, public RegAllocBase
 
   // state
   std::auto_ptr<Spiller> SpillerInstance;
-
+  std::priority_queue<LiveInterval*, std::vector<LiveInterval*>,
+                      CompSpillWeight> Queue;
 public:
   RABasic();
 
@@ -100,6 +110,18 @@ public:
 
   virtual float getPriority(LiveInterval *LI) { return LI->weight; }
 
+  virtual void enqueue(LiveInterval *LI) {
+    Queue.push(LI);
+  }
+
+  virtual LiveInterval *dequeue() {
+    if (Queue.empty())
+      return 0;
+    LiveInterval *LI = Queue.top();
+    Queue.pop();
+    return LI;
+  }
+
   virtual unsigned selectOrSplit(LiveInterval &VirtReg,
                                  SmallVectorImpl<LiveInterval*> &SplitVRegs);
 
@@ -227,18 +249,17 @@ void RegAllocBase::releaseMemory() {
   PhysReg2LiveUnion.clear();
 }
 
-// Visit all the live virtual registers. If they are already assigned to a
-// physical register, unify them with the corresponding LiveIntervalUnion,
-// otherwise push them on the priority queue for later assignment.
-void RegAllocBase::
-seedLiveVirtRegs(std::priority_queue<std::pair<float, unsigned> > &VirtRegQ) {
+// Visit all the live registers. If they are already assigned to a physical
+// register, unify them with the corresponding LiveIntervalUnion, otherwise push
+// them on the priority queue for later assignment.
+void RegAllocBase::seedLiveRegs() {
   for (LiveIntervals::iterator I = LIS->begin(), E = LIS->end(); I != E; ++I) {
     unsigned RegNum = I->first;
     LiveInterval &VirtReg = *I->second;
     if (TargetRegisterInfo::isPhysicalRegister(RegNum))
       PhysReg2LiveUnion[RegNum].unify(VirtReg);
     else
-      VirtRegQ.push(std::make_pair(getPriority(&VirtReg), RegNum));
+      enqueue(&VirtReg);
   }
 }
 
@@ -263,38 +284,31 @@ void RegAllocBase::unassign(LiveInterval &VirtReg, unsigned PhysReg) {
 // Top-level driver to manage the queue of unassigned VirtRegs and call the
 // selectOrSplit implementation.
 void RegAllocBase::allocatePhysRegs() {
-
-  // Push each vreg onto a queue or "precolor" by adding it to a physreg union.
-  std::priority_queue<std::pair<float, unsigned> > VirtRegQ;
-  seedLiveVirtRegs(VirtRegQ);
+  seedLiveRegs();
 
   // Continue assigning vregs one at a time to available physical registers.
-  while (!VirtRegQ.empty()) {
-    // Pop the highest priority vreg.
-    LiveInterval &VirtReg = LIS->getInterval(VirtRegQ.top().second);
-    VirtRegQ.pop();
-
+  while (LiveInterval *VirtReg = dequeue()) {
     // selectOrSplit requests the allocator to return an available physical
     // register if possible and populate a list of new live intervals that
     // result from splitting.
-    DEBUG(dbgs() << "\nselectOrSplit " << MRI->getRegClass(VirtReg.reg)->getName()
-                 << ':' << VirtReg << '\n');
+    DEBUG(dbgs() << "\nselectOrSplit "
+                 << MRI->getRegClass(VirtReg->reg)->getName()
+                 << ':' << *VirtReg << '\n');
     typedef SmallVector<LiveInterval*, 4> VirtRegVec;
     VirtRegVec SplitVRegs;
-    unsigned AvailablePhysReg = selectOrSplit(VirtReg, SplitVRegs);
+    unsigned AvailablePhysReg = selectOrSplit(*VirtReg, SplitVRegs);
 
     if (AvailablePhysReg)
-      assign(VirtReg, AvailablePhysReg);
+      assign(*VirtReg, AvailablePhysReg);
 
     for (VirtRegVec::iterator I = SplitVRegs.begin(), E = SplitVRegs.end();
          I != E; ++I) {
-      LiveInterval* SplitVirtReg = *I;
+      LiveInterval *SplitVirtReg = *I;
       if (SplitVirtReg->empty()) continue;
       DEBUG(dbgs() << "queuing new interval: " << *SplitVirtReg << "\n");
       assert(TargetRegisterInfo::isVirtualRegister(SplitVirtReg->reg) &&
              "expect split value in virtual register");
-      VirtRegQ.push(std::make_pair(getPriority(SplitVirtReg),
-                                   SplitVirtReg->reg));
+      enqueue(SplitVirtReg);
       ++NumNewQueued;
     }
   }