CalcSpillWeights.cpp revision e264f62ca09a8f65c87a46d562a4d0f9ec5d457e
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/TargetMachine.h" 24#include "llvm/Target/TargetRegisterInfo.h" 25using namespace llvm; 26 27char CalculateSpillWeights::ID = 0; 28static RegisterPass<CalculateSpillWeights> X("calcspillweights", 29 "Calculate spill weights"); 30 31void CalculateSpillWeights::getAnalysisUsage(AnalysisUsage &au) const { 32 au.addRequired<LiveIntervals>(); 33 au.addRequired<MachineLoopInfo>(); 34 au.setPreservesAll(); 35 MachineFunctionPass::getAnalysisUsage(au); 36} 37 38bool 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) || mi->isImplicitDef() || mi->isDebugValue()) 62 continue; 63 64 for (unsigned i = 0, e = mi->getNumOperands(); i != e; ++i) { 65 const MachineOperand &mopi = mi->getOperand(i); 66 if (!mopi.isReg() || mopi.getReg() == 0) 67 continue; 68 unsigned reg = mopi.getReg(); 69 if (!TargetRegisterInfo::isVirtualRegister(mopi.getReg())) 70 continue; 71 // Multiple uses of reg by the same instruction. It should not 72 // contribute to spill weight again. 73 if (!processed.insert(reg)) 74 continue; 75 76 bool hasDef = mopi.isDef(); 77 bool hasUse = !hasDef; 78 for (unsigned j = i+1; j != e; ++j) { 79 const MachineOperand &mopj = mi->getOperand(j); 80 if (!mopj.isReg() || mopj.getReg() != reg) 81 continue; 82 hasDef |= mopj.isDef(); 83 hasUse |= mopj.isUse(); 84 if (hasDef && hasUse) 85 break; 86 } 87 88 LiveInterval ®Int = lis->getInterval(reg); 89 float weight = lis->getSpillWeight(hasDef, hasUse, loopDepth); 90 if (hasDef && isExiting) { 91 // Looks like this is a loop count variable update. 92 SlotIndex defIdx = lis->getInstructionIndex(mi).getDefIndex(); 93 const LiveRange *dlr = 94 lis->getInterval(reg).getLiveRangeContaining(defIdx); 95 if (dlr->end >= mbbEnd) 96 weight *= 3.0F; 97 } 98 regInt.weight += weight; 99 } 100 processed.clear(); 101 } 102 } 103 104 for (LiveIntervals::iterator I = lis->begin(), E = lis->end(); I != E; ++I) { 105 LiveInterval &li = *I->second; 106 if (TargetRegisterInfo::isVirtualRegister(li.reg)) { 107 // If the live interval length is essentially zero, i.e. in every live 108 // range the use follows def immediately, it doesn't make sense to spill 109 // it and hope it will be easier to allocate for this li. 110 if (isZeroLengthInterval(&li)) { 111 li.weight = HUGE_VALF; 112 continue; 113 } 114 115 bool isLoad = false; 116 SmallVector<LiveInterval*, 4> spillIs; 117 if (lis->isReMaterializable(li, spillIs, isLoad)) { 118 // If all of the definitions of the interval are re-materializable, 119 // it is a preferred candidate for spilling. If non of the defs are 120 // loads, then it's potentially very cheap to re-materialize. 121 // FIXME: this gets much more complicated once we support non-trivial 122 // re-materialization. 123 if (isLoad) 124 li.weight *= 0.9F; 125 else 126 li.weight *= 0.5F; 127 } 128 129 // Slightly prefer live interval that has been assigned a preferred reg. 130 std::pair<unsigned, unsigned> Hint = mri->getRegAllocationHint(li.reg); 131 if (Hint.first || Hint.second) 132 li.weight *= 1.01F; 133 134 // Divide the weight of the interval by its size. This encourages 135 // spilling of intervals that are large and have few uses, and 136 // discourages spilling of small intervals with many uses. 137 li.weight /= lis->getApproximateInstructionCount(li) * SlotIndex::NUM; 138 } 139 } 140 141 return false; 142} 143 144/// Returns true if the given live interval is zero length. 145bool CalculateSpillWeights::isZeroLengthInterval(LiveInterval *li) const { 146 for (LiveInterval::Ranges::const_iterator 147 i = li->ranges.begin(), e = li->ranges.end(); i != e; ++i) 148 if (i->end.getPrevIndex() > i->start) 149 return false; 150 return true; 151} 152