CalcSpillWeights.cpp revision 263508
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/CodeGen/CalcSpillWeights.h" 13#include "llvm/CodeGen/LiveIntervalAnalysis.h" 14#include "llvm/CodeGen/MachineBlockFrequencyInfo.h" 15#include "llvm/CodeGen/MachineFunction.h" 16#include "llvm/CodeGen/MachineLoopInfo.h" 17#include "llvm/CodeGen/MachineRegisterInfo.h" 18#include "llvm/Support/Debug.h" 19#include "llvm/Support/raw_ostream.h" 20#include "llvm/Target/TargetInstrInfo.h" 21#include "llvm/Target/TargetMachine.h" 22#include "llvm/Target/TargetRegisterInfo.h" 23using namespace llvm; 24 25void llvm::calculateSpillWeightsAndHints(LiveIntervals &LIS, 26 MachineFunction &MF, 27 const MachineLoopInfo &MLI, 28 const MachineBlockFrequencyInfo &MBFI, 29 VirtRegAuxInfo::NormalizingFn norm) { 30 DEBUG(dbgs() << "********** Compute Spill Weights **********\n" 31 << "********** Function: " << MF.getName() << '\n'); 32 33 MachineRegisterInfo &MRI = MF.getRegInfo(); 34 VirtRegAuxInfo VRAI(MF, LIS, MLI, MBFI, norm); 35 for (unsigned i = 0, e = MRI.getNumVirtRegs(); i != e; ++i) { 36 unsigned Reg = TargetRegisterInfo::index2VirtReg(i); 37 if (MRI.reg_nodbg_empty(Reg)) 38 continue; 39 VRAI.calculateSpillWeightAndHint(LIS.getInterval(Reg)); 40 } 41} 42 43// Return the preferred allocation register for reg, given a COPY instruction. 44static unsigned copyHint(const MachineInstr *mi, unsigned reg, 45 const TargetRegisterInfo &tri, 46 const MachineRegisterInfo &mri) { 47 unsigned sub, hreg, hsub; 48 if (mi->getOperand(0).getReg() == reg) { 49 sub = mi->getOperand(0).getSubReg(); 50 hreg = mi->getOperand(1).getReg(); 51 hsub = mi->getOperand(1).getSubReg(); 52 } else { 53 sub = mi->getOperand(1).getSubReg(); 54 hreg = mi->getOperand(0).getReg(); 55 hsub = mi->getOperand(0).getSubReg(); 56 } 57 58 if (!hreg) 59 return 0; 60 61 if (TargetRegisterInfo::isVirtualRegister(hreg)) 62 return sub == hsub ? hreg : 0; 63 64 const TargetRegisterClass *rc = mri.getRegClass(reg); 65 66 // Only allow physreg hints in rc. 67 if (sub == 0) 68 return rc->contains(hreg) ? hreg : 0; 69 70 // reg:sub should match the physreg hreg. 71 return tri.getMatchingSuperReg(hreg, sub, rc); 72} 73 74// Check if all values in LI are rematerializable 75static bool isRematerializable(const LiveInterval &LI, 76 const LiveIntervals &LIS, 77 const TargetInstrInfo &TII) { 78 for (LiveInterval::const_vni_iterator I = LI.vni_begin(), E = LI.vni_end(); 79 I != E; ++I) { 80 const VNInfo *VNI = *I; 81 if (VNI->isUnused()) 82 continue; 83 if (VNI->isPHIDef()) 84 return false; 85 86 MachineInstr *MI = LIS.getInstructionFromIndex(VNI->def); 87 assert(MI && "Dead valno in interval"); 88 89 if (!TII.isTriviallyReMaterializable(MI, LIS.getAliasAnalysis())) 90 return false; 91 } 92 return true; 93} 94 95void 96VirtRegAuxInfo::calculateSpillWeightAndHint(LiveInterval &li) { 97 MachineRegisterInfo &mri = MF.getRegInfo(); 98 const TargetRegisterInfo &tri = *MF.getTarget().getRegisterInfo(); 99 MachineBasicBlock *mbb = 0; 100 MachineLoop *loop = 0; 101 bool isExiting = false; 102 float totalWeight = 0; 103 SmallPtrSet<MachineInstr*, 8> visited; 104 105 // Find the best physreg hint and the best virtreg hint. 106 float bestPhys = 0, bestVirt = 0; 107 unsigned hintPhys = 0, hintVirt = 0; 108 109 // Don't recompute a target specific hint. 110 bool noHint = mri.getRegAllocationHint(li.reg).first != 0; 111 112 // Don't recompute spill weight for an unspillable register. 113 bool Spillable = li.isSpillable(); 114 115 for (MachineRegisterInfo::reg_iterator I = mri.reg_begin(li.reg); 116 MachineInstr *mi = I.skipInstruction();) { 117 if (mi->isIdentityCopy() || mi->isImplicitDef() || mi->isDebugValue()) 118 continue; 119 if (!visited.insert(mi)) 120 continue; 121 122 float weight = 1.0f; 123 if (Spillable) { 124 // Get loop info for mi. 125 if (mi->getParent() != mbb) { 126 mbb = mi->getParent(); 127 loop = Loops.getLoopFor(mbb); 128 isExiting = loop ? loop->isLoopExiting(mbb) : false; 129 } 130 131 // Calculate instr weight. 132 bool reads, writes; 133 tie(reads, writes) = mi->readsWritesVirtualRegister(li.reg); 134 weight = LiveIntervals::getSpillWeight( 135 writes, reads, MBFI.getBlockFreq(mi->getParent())); 136 137 // Give extra weight to what looks like a loop induction variable update. 138 if (writes && isExiting && LIS.isLiveOutOfMBB(li, mbb)) 139 weight *= 3; 140 141 totalWeight += weight; 142 } 143 144 // Get allocation hints from copies. 145 if (noHint || !mi->isCopy()) 146 continue; 147 unsigned hint = copyHint(mi, li.reg, tri, mri); 148 if (!hint) 149 continue; 150 float hweight = Hint[hint] += weight; 151 if (TargetRegisterInfo::isPhysicalRegister(hint)) { 152 if (hweight > bestPhys && mri.isAllocatable(hint)) 153 bestPhys = hweight, hintPhys = hint; 154 } else { 155 if (hweight > bestVirt) 156 bestVirt = hweight, hintVirt = hint; 157 } 158 } 159 160 Hint.clear(); 161 162 // Always prefer the physreg hint. 163 if (unsigned hint = hintPhys ? hintPhys : hintVirt) { 164 mri.setRegAllocationHint(li.reg, 0, hint); 165 // Weakly boost the spill weight of hinted registers. 166 totalWeight *= 1.01F; 167 } 168 169 // If the live interval was already unspillable, leave it that way. 170 if (!Spillable) 171 return; 172 173 // Mark li as unspillable if all live ranges are tiny. 174 if (li.isZeroLength(LIS.getSlotIndexes())) { 175 li.markNotSpillable(); 176 return; 177 } 178 179 // If all of the definitions of the interval are re-materializable, 180 // it is a preferred candidate for spilling. 181 // FIXME: this gets much more complicated once we support non-trivial 182 // re-materialization. 183 if (isRematerializable(li, LIS, *MF.getTarget().getInstrInfo())) 184 totalWeight *= 0.5F; 185 186 li.weight = normalize(totalWeight, li.getSize()); 187} 188