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 #include "llvm/CodeGen/VirtRegMap.h" 11 #include "llvm/CodeGen/CalcSpillWeights.h" 12 #include "llvm/CodeGen/LiveIntervalAnalysis.h" 13 #include "llvm/CodeGen/MachineBlockFrequencyInfo.h" 14 #include "llvm/CodeGen/MachineFunction.h" 15 #include "llvm/CodeGen/MachineLoopInfo.h" 16 #include "llvm/CodeGen/MachineRegisterInfo.h" 17 #include "llvm/Support/Debug.h" 18 #include "llvm/Support/raw_ostream.h" 19 #include "llvm/Target/TargetInstrInfo.h" 20 #include "llvm/Target/TargetRegisterInfo.h" 21 #include "llvm/Target/TargetSubtargetInfo.h" 22 using namespace llvm; 23 24 #define DEBUG_TYPE "calcspillweights" 25 26 void llvm::calculateSpillWeightsAndHints(LiveIntervals &LIS, 27 MachineFunction &MF, 28 VirtRegMap *VRM, 29 const MachineLoopInfo &MLI, 30 const MachineBlockFrequencyInfo &MBFI, 31 VirtRegAuxInfo::NormalizingFn norm) { 32 DEBUG(dbgs() << "********** Compute Spill Weights **********\n" 33 << "********** Function: " << MF.getName() << '\n'); 34 35 MachineRegisterInfo &MRI = MF.getRegInfo(); 36 VirtRegAuxInfo VRAI(MF, LIS, VRM, MLI, MBFI, norm); 37 for (unsigned i = 0, e = MRI.getNumVirtRegs(); i != e; ++i) { 38 unsigned Reg = TargetRegisterInfo::index2VirtReg(i); 39 if (MRI.reg_nodbg_empty(Reg)) 40 continue; 41 VRAI.calculateSpillWeightAndHint(LIS.getInterval(Reg)); 42 } 43 } 44 45 // Return the preferred allocation register for reg, given a COPY instruction. 46 static unsigned copyHint(const MachineInstr *mi, unsigned reg, 47 const TargetRegisterInfo &tri, 48 const MachineRegisterInfo &mri) { 49 unsigned sub, hreg, hsub; 50 if (mi->getOperand(0).getReg() == reg) { 51 sub = mi->getOperand(0).getSubReg(); 52 hreg = mi->getOperand(1).getReg(); 53 hsub = mi->getOperand(1).getSubReg(); 54 } else { 55 sub = mi->getOperand(1).getSubReg(); 56 hreg = mi->getOperand(0).getReg(); 57 hsub = mi->getOperand(0).getSubReg(); 58 } 59 60 if (!hreg) 61 return 0; 62 63 if (TargetRegisterInfo::isVirtualRegister(hreg)) 64 return sub == hsub ? hreg : 0; 65 66 const TargetRegisterClass *rc = mri.getRegClass(reg); 67 68 // Only allow physreg hints in rc. 69 if (sub == 0) 70 return rc->contains(hreg) ? hreg : 0; 71 72 // reg:sub should match the physreg hreg. 73 return tri.getMatchingSuperReg(hreg, sub, rc); 74 } 75 76 // Check if all values in LI are rematerializable 77 static bool isRematerializable(const LiveInterval &LI, 78 const LiveIntervals &LIS, 79 VirtRegMap *VRM, 80 const TargetInstrInfo &TII) { 81 unsigned Reg = LI.reg; 82 unsigned Original = VRM ? VRM->getOriginal(Reg) : 0; 83 for (LiveInterval::const_vni_iterator I = LI.vni_begin(), E = LI.vni_end(); 84 I != E; ++I) { 85 const VNInfo *VNI = *I; 86 if (VNI->isUnused()) 87 continue; 88 if (VNI->isPHIDef()) 89 return false; 90 91 MachineInstr *MI = LIS.getInstructionFromIndex(VNI->def); 92 assert(MI && "Dead valno in interval"); 93 94 // Trace copies introduced by live range splitting. The inline 95 // spiller can rematerialize through these copies, so the spill 96 // weight must reflect this. 97 if (VRM) { 98 while (MI->isFullCopy()) { 99 // The copy destination must match the interval register. 100 if (MI->getOperand(0).getReg() != Reg) 101 return false; 102 103 // Get the source register. 104 Reg = MI->getOperand(1).getReg(); 105 106 // If the original (pre-splitting) registers match this 107 // copy came from a split. 108 if (!TargetRegisterInfo::isVirtualRegister(Reg) || 109 VRM->getOriginal(Reg) != Original) 110 return false; 111 112 // Follow the copy live-in value. 113 const LiveInterval &SrcLI = LIS.getInterval(Reg); 114 LiveQueryResult SrcQ = SrcLI.Query(VNI->def); 115 VNI = SrcQ.valueIn(); 116 assert(VNI && "Copy from non-existing value"); 117 if (VNI->isPHIDef()) 118 return false; 119 MI = LIS.getInstructionFromIndex(VNI->def); 120 assert(MI && "Dead valno in interval"); 121 } 122 } 123 124 if (!TII.isTriviallyReMaterializable(MI, LIS.getAliasAnalysis())) 125 return false; 126 } 127 return true; 128 } 129 130 void 131 VirtRegAuxInfo::calculateSpillWeightAndHint(LiveInterval &li) { 132 MachineRegisterInfo &mri = MF.getRegInfo(); 133 const TargetRegisterInfo &tri = *MF.getSubtarget().getRegisterInfo(); 134 MachineBasicBlock *mbb = nullptr; 135 MachineLoop *loop = nullptr; 136 bool isExiting = false; 137 float totalWeight = 0; 138 unsigned numInstr = 0; // Number of instructions using li 139 SmallPtrSet<MachineInstr*, 8> visited; 140 141 // Find the best physreg hint and the best virtreg hint. 142 float bestPhys = 0, bestVirt = 0; 143 unsigned hintPhys = 0, hintVirt = 0; 144 145 // Don't recompute a target specific hint. 146 bool noHint = mri.getRegAllocationHint(li.reg).first != 0; 147 148 // Don't recompute spill weight for an unspillable register. 149 bool Spillable = li.isSpillable(); 150 151 for (MachineRegisterInfo::reg_instr_iterator 152 I = mri.reg_instr_begin(li.reg), E = mri.reg_instr_end(); 153 I != E; ) { 154 MachineInstr *mi = &*(I++); 155 numInstr++; 156 if (mi->isIdentityCopy() || mi->isImplicitDef() || mi->isDebugValue()) 157 continue; 158 if (!visited.insert(mi).second) 159 continue; 160 161 float weight = 1.0f; 162 if (Spillable) { 163 // Get loop info for mi. 164 if (mi->getParent() != mbb) { 165 mbb = mi->getParent(); 166 loop = Loops.getLoopFor(mbb); 167 isExiting = loop ? loop->isLoopExiting(mbb) : false; 168 } 169 170 // Calculate instr weight. 171 bool reads, writes; 172 std::tie(reads, writes) = mi->readsWritesVirtualRegister(li.reg); 173 weight = LiveIntervals::getSpillWeight( 174 writes, reads, &MBFI, mi); 175 176 // Give extra weight to what looks like a loop induction variable update. 177 if (writes && isExiting && LIS.isLiveOutOfMBB(li, mbb)) 178 weight *= 3; 179 180 totalWeight += weight; 181 } 182 183 // Get allocation hints from copies. 184 if (noHint || !mi->isCopy()) 185 continue; 186 unsigned hint = copyHint(mi, li.reg, tri, mri); 187 if (!hint) 188 continue; 189 // Force hweight onto the stack so that x86 doesn't add hidden precision, 190 // making the comparison incorrectly pass (i.e., 1 > 1 == true??). 191 // 192 // FIXME: we probably shouldn't use floats at all. 193 volatile float hweight = Hint[hint] += weight; 194 if (TargetRegisterInfo::isPhysicalRegister(hint)) { 195 if (hweight > bestPhys && mri.isAllocatable(hint)) 196 bestPhys = hweight, hintPhys = hint; 197 } else { 198 if (hweight > bestVirt) 199 bestVirt = hweight, hintVirt = hint; 200 } 201 } 202 203 Hint.clear(); 204 205 // Always prefer the physreg hint. 206 if (unsigned hint = hintPhys ? hintPhys : hintVirt) { 207 mri.setRegAllocationHint(li.reg, 0, hint); 208 // Weakly boost the spill weight of hinted registers. 209 totalWeight *= 1.01F; 210 } 211 212 // If the live interval was already unspillable, leave it that way. 213 if (!Spillable) 214 return; 215 216 // Mark li as unspillable if all live ranges are tiny. 217 if (li.isZeroLength(LIS.getSlotIndexes())) { 218 li.markNotSpillable(); 219 return; 220 } 221 222 // If all of the definitions of the interval are re-materializable, 223 // it is a preferred candidate for spilling. 224 // FIXME: this gets much more complicated once we support non-trivial 225 // re-materialization. 226 if (isRematerializable(li, LIS, VRM, *MF.getSubtarget().getInstrInfo())) 227 totalWeight *= 0.5F; 228 229 li.weight = normalize(totalWeight, li.getSize(), numInstr); 230 } 231
