1 //===------------------------ CalcSpillWeights.cpp ------------------------===// 2 // 3 // The LLVM Compiler Infrastructure 4 // 5 // This file is distributed under the University of Illinois Open Source 6 // License. See LICENSE.TXT for details. 7 // 8 //===----------------------------------------------------------------------===// 9 10 #define DEBUG_TYPE "calcspillweights" 11 12 #include "llvm/Function.h" 13 #include "llvm/ADT/SmallSet.h" 14 #include "llvm/CodeGen/CalcSpillWeights.h" 15 #include "llvm/CodeGen/LiveIntervalAnalysis.h" 16 #include "llvm/CodeGen/MachineFunction.h" 17 #include "llvm/CodeGen/MachineLoopInfo.h" 18 #include "llvm/CodeGen/MachineRegisterInfo.h" 19 #include "llvm/CodeGen/SlotIndexes.h" 20 #include "llvm/Support/Debug.h" 21 #include "llvm/Support/raw_ostream.h" 22 #include "llvm/Target/TargetInstrInfo.h" 23 #include "llvm/Target/TargetRegisterInfo.h" 24 25 using namespace llvm; 26 27 char CalculateSpillWeights::ID = 0; 28 static RegisterPass<CalculateSpillWeights> X("calcspillweights", 29 "Calculate spill weights"); 30 31 void CalculateSpillWeights::getAnalysisUsage(AnalysisUsage &au) const { 32 au.addRequired<LiveIntervals>(); 33 au.addRequired<MachineLoopInfo>(); 34 au.setPreservesAll(); 35 MachineFunctionPass::getAnalysisUsage(au); 36 } 37 38 bool CalculateSpillWeights::runOnMachineFunction(MachineFunction &fn) { 39 40 DEBUG(dbgs() << "********** Compute Spill Weights **********\n" 41 << "********** Function: " 42 << fn.getFunction()->getName() << '\n'); 43 44 LiveIntervals *lis = &getAnalysis<LiveIntervals>(); 45 MachineLoopInfo *loopInfo = &getAnalysis<MachineLoopInfo>(); 46 const TargetInstrInfo *tii = fn.getTarget().getInstrInfo(); 47 MachineRegisterInfo *mri = &fn.getRegInfo(); 48 49 SmallSet<unsigned, 4> processed; 50 for (MachineFunction::iterator mbbi = fn.begin(), mbbe = fn.end(); 51 mbbi != mbbe; ++mbbi) { 52 MachineBasicBlock* mbb = mbbi; 53 SlotIndex mbbEnd = lis->getMBBEndIdx(mbb); 54 MachineLoop* loop = loopInfo->getLoopFor(mbb); 55 unsigned loopDepth = loop ? loop->getLoopDepth() : 0; 56 bool isExiting = loop ? loop->isLoopExiting(mbb) : false; 57 58 for (MachineBasicBlock::const_iterator mii = mbb->begin(), mie = mbb->end(); 59 mii != mie; ++mii) { 60 const MachineInstr *mi = mii; 61 if (tii->isIdentityCopy(*mi)) 62 continue; 63 64 if (mi->getOpcode() == TargetInstrInfo::IMPLICIT_DEF) 65 continue; 66 67 for (unsigned i = 0, e = mi->getNumOperands(); i != e; ++i) { 68 const MachineOperand &mopi = mi->getOperand(i); 69 if (!mopi.isReg() || mopi.getReg() == 0) 70 continue; 71 unsigned reg = mopi.getReg(); 72 if (!TargetRegisterInfo::isVirtualRegister(mopi.getReg())) 73 continue; 74 // Multiple uses of reg by the same instruction. It should not 75 // contribute to spill weight again. 76 if (!processed.insert(reg)) 77 continue; 78 79 bool hasDef = mopi.isDef(); 80 bool hasUse = !hasDef; 81 for (unsigned j = i+1; j != e; ++j) { 82 const MachineOperand &mopj = mi->getOperand(j); 83 if (!mopj.isReg() || mopj.getReg() != reg) 84 continue; 85 hasDef |= mopj.isDef(); 86 hasUse |= mopj.isUse(); 87 if (hasDef && hasUse) 88 break; 89 } 90 91 LiveInterval ®Int = lis->getInterval(reg); 92 float weight = lis->getSpillWeight(hasDef, hasUse, loopDepth); 93 if (hasDef && isExiting) { 94 // Looks like this is a loop count variable update. 95 SlotIndex defIdx = lis->getInstructionIndex(mi).getDefIndex(); 96 const LiveRange *dlr = 97 lis->getInterval(reg).getLiveRangeContaining(defIdx); 98 if (dlr->end >= mbbEnd) 99 weight *= 3.0F; 100 } 101 regInt.weight += weight; 102 } 103 processed.clear(); 104 } 105 } 106 107 for (LiveIntervals::iterator I = lis->begin(), E = lis->end(); I != E; ++I) { 108 LiveInterval &li = *I->second; 109 if (TargetRegisterInfo::isVirtualRegister(li.reg)) { 110 // If the live interval length is essentially zero, i.e. in every live 111 // range the use follows def immediately, it doesn't make sense to spill 112 // it and hope it will be easier to allocate for this li. 113 if (isZeroLengthInterval(&li)) { 114 li.weight = HUGE_VALF; 115 continue; 116 } 117 118 bool isLoad = false; 119 SmallVector<LiveInterval*, 4> spillIs; 120 if (lis->isReMaterializable(li, spillIs, isLoad)) { 121 // If all of the definitions of the interval are re-materializable, 122 // it is a preferred candidate for spilling. If non of the defs are 123 // loads, then it's potentially very cheap to re-materialize. 124 // FIXME: this gets much more complicated once we support non-trivial 125 // re-materialization. 126 if (isLoad) 127 li.weight *= 0.9F; 128 else 129 li.weight *= 0.5F; 130 } 131 132 // Slightly prefer live interval that has been assigned a preferred reg. 133 std::pair<unsigned, unsigned> Hint = mri->getRegAllocationHint(li.reg); 134 if (Hint.first || Hint.second) 135 li.weight *= 1.01F; 136 137 // Divide the weight of the interval by its size. This encourages 138 // spilling of intervals that are large and have few uses, and 139 // discourages spilling of small intervals with many uses. 140 li.weight /= lis->getApproximateInstructionCount(li) * SlotIndex::NUM; 141 } 142 } 143 144 return false; 145 } 146 147 /// Returns true if the given live interval is zero length. 148 bool CalculateSpillWeights::isZeroLengthInterval(LiveInterval *li) const { 149 for (LiveInterval::Ranges::const_iterator 150 i = li->ranges.begin(), e = li->ranges.end(); i != e; ++i) 151 if (i->end.getPrevIndex() > i->start) 152 return false; 153 return true; 154 } 155