From d0bec3e62c98b1f0ef3a41db8f95599b2014c131 Mon Sep 17 00:00:00 2001
From: Jakob Stoklund Olesen <stoklund@2pi.dk>
Date: Wed, 8 Dec 2010 22:22:41 +0000
Subject: Store (priority,regnum) pairs in the priority queue instead of
 providing an abstract priority queue interface in subclasses that want to
 override the priority calculations.

Subclasses must provide a getPriority() implementation instead.

This approach requires less code as long as priorities are expressable as simple
floats, and it avoids the dangers of defining potentially expensive priority
comparison functions.

It also should speed up priority_queue operations since they no longer have to
chase pointers when comparing registers. This is not measurable, though.

Preferably, we shouldn't use floats to guide code generation. The use of floats
here is derived from the use of floats for spill weights. Spill weights have a
dynamic range that doesn't lend itself easily to a fixpoint implementation.

When someone invents a stable spill weight representation, it can be reused for
allocation priorities.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@121294 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/CodeGen/RegAllocBasic.cpp | 63 ++++++++++++-------------------------------
 1 file changed, 17 insertions(+), 46 deletions(-)

(limited to 'lib/CodeGen/RegAllocBasic.cpp')

diff --git a/lib/CodeGen/RegAllocBasic.cpp b/lib/CodeGen/RegAllocBasic.cpp
index d0e6355129..88446aa505 100644
--- a/lib/CodeGen/RegAllocBasic.cpp
+++ b/lib/CodeGen/RegAllocBasic.cpp
@@ -43,8 +43,6 @@
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/raw_ostream.h"
 
-#include <vector>
-#include <queue>
 #include <cstdlib>
 
 using namespace llvm;
@@ -103,6 +101,8 @@ public:
 
   virtual Spiller &spiller() { return *SpillerInstance; }
 
+  virtual float getPriority(LiveInterval *LI) { return LI->weight; }
+
   virtual unsigned selectOrSplit(LiveInterval &VirtReg,
                                  SmallVectorImpl<LiveInterval*> &SplitVRegs);
 
@@ -230,49 +230,18 @@ void RegAllocBase::releaseMemory() {
   PhysReg2LiveUnion.clear();
 }
 
-namespace llvm {
-/// This class defines a queue of live virtual registers prioritized by spill
-/// weight. The heaviest vreg is popped first.
-///
-/// Currently, this is trivial wrapper that gives us an opaque type in the
-/// header, but we may later give it a virtual interface for register allocators
-/// to override the priority queue comparator.
-class LiveVirtRegQueue {
-  typedef std::priority_queue
-    <LiveInterval*, std::vector<LiveInterval*>, LessSpillWeightPriority>
-    PriorityQ;
-  PriorityQ PQ;
-
-public:
-  // Is the queue empty?
-  bool empty() { return PQ.empty(); }
-
-  // Get the highest priority lvr (top + pop)
-  LiveInterval *get() {
-    LiveInterval *VirtReg = PQ.top();
-    PQ.pop();
-    return VirtReg;
-  }
-  // Add this lvr to the queue
-  void push(LiveInterval *VirtReg) {
-    PQ.push(VirtReg);
-  }
-};
-} // end namespace llvm
-
 // 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(LiveVirtRegQueue &VirtRegQ) {
+void RegAllocBase::
+seedLiveVirtRegs(std::priority_queue<std::pair<float, unsigned> > &VirtRegQ) {
   for (LiveIntervals::iterator I = LIS->begin(), E = LIS->end(); I != E; ++I) {
     unsigned RegNum = I->first;
     LiveInterval &VirtReg = *I->second;
-    if (TargetRegisterInfo::isPhysicalRegister(RegNum)) {
+    if (TargetRegisterInfo::isPhysicalRegister(RegNum))
       PhysReg2LiveUnion[RegNum].unify(VirtReg);
-    }
-    else {
-      VirtRegQ.push(&VirtReg);
-    }
+    else
+      VirtRegQ.push(std::make_pair(getPriority(&VirtReg), RegNum));
   }
 }
 
@@ -281,27 +250,28 @@ void RegAllocBase::seedLiveVirtRegs(LiveVirtRegQueue &VirtRegQ) {
 void RegAllocBase::allocatePhysRegs() {
 
   // Push each vreg onto a queue or "precolor" by adding it to a physreg union.
-  LiveVirtRegQueue VirtRegQ;
+  std::priority_queue<std::pair<float, unsigned> > VirtRegQ;
   seedLiveVirtRegs(VirtRegQ);
 
   // Continue assigning vregs one at a time to available physical registers.
   while (!VirtRegQ.empty()) {
     // Pop the highest priority vreg.
-    LiveInterval *VirtReg = VirtRegQ.get();
+    LiveInterval &VirtReg = LIS->getInterval(VirtRegQ.top().second);
+    VirtRegQ.pop();
 
     // selectOrSplit requests the allocator to return an available physical
     // register if possible and populate a list of new live intervals that
     // result from splitting.
     typedef SmallVector<LiveInterval*, 4> VirtRegVec;
     VirtRegVec SplitVRegs;
-    unsigned AvailablePhysReg = selectOrSplit(*VirtReg, SplitVRegs);
+    unsigned AvailablePhysReg = selectOrSplit(VirtReg, SplitVRegs);
 
     if (AvailablePhysReg) {
       DEBUG(dbgs() << "allocating: " << TRI->getName(AvailablePhysReg) <<
-            " " << *VirtReg << '\n');
-      assert(!VRM->hasPhys(VirtReg->reg) && "duplicate vreg in union");
-      VRM->assignVirt2Phys(VirtReg->reg, AvailablePhysReg);
-      PhysReg2LiveUnion[AvailablePhysReg].unify(*VirtReg);
+            " " << VirtReg << '\n');
+      assert(!VRM->hasPhys(VirtReg.reg) && "duplicate vreg in union");
+      VRM->assignVirt2Phys(VirtReg.reg, AvailablePhysReg);
+      PhysReg2LiveUnion[AvailablePhysReg].unify(VirtReg);
     }
     for (VirtRegVec::iterator I = SplitVRegs.begin(), E = SplitVRegs.end();
          I != E; ++I) {
@@ -310,7 +280,8 @@ void RegAllocBase::allocatePhysRegs() {
       DEBUG(dbgs() << "queuing new interval: " << *SplitVirtReg << "\n");
       assert(TargetRegisterInfo::isVirtualRegister(SplitVirtReg->reg) &&
              "expect split value in virtual register");
-      VirtRegQ.push(SplitVirtReg);
+      VirtRegQ.push(std::make_pair(getPriority(SplitVirtReg),
+                                   SplitVirtReg->reg));
     }
   }
 }
-- 
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