1 //===-- RegisterClassInfo.cpp - Dynamic Register Class Info ---------------===// 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 // This file implements the RegisterClassInfo class which provides dynamic 11 // information about target register classes. Callee-saved vs. caller-saved and 12 // reserved registers depend on calling conventions and other dynamic 13 // information, so some things cannot be determined statically. 14 // 15 //===----------------------------------------------------------------------===// 16 17 #include "llvm/CodeGen/RegisterClassInfo.h" 18 #include "llvm/CodeGen/MachineFunction.h" 19 #include "llvm/CodeGen/MachineRegisterInfo.h" 20 #include "llvm/Support/CommandLine.h" 21 #include "llvm/Support/Debug.h" 22 #include "llvm/Support/raw_ostream.h" 23 #include "llvm/Target/TargetMachine.h" 24 25 using namespace llvm; 26 27 #define DEBUG_TYPE "regalloc" 28 29 static cl::opt<unsigned> 30 StressRA("stress-regalloc", cl::Hidden, cl::init(0), cl::value_desc("N"), 31 cl::desc("Limit all regclasses to N registers")); 32 33 RegisterClassInfo::RegisterClassInfo() 34 : Tag(0), MF(nullptr), TRI(nullptr), CalleeSaved(nullptr) {} 35 36 void RegisterClassInfo::runOnMachineFunction(const MachineFunction &mf) { 37 bool Update = false; 38 MF = &mf; 39 40 // Allocate new array the first time we see a new target. 41 if (MF->getTarget().getRegisterInfo() != TRI) { 42 TRI = MF->getTarget().getRegisterInfo(); 43 RegClass.reset(new RCInfo[TRI->getNumRegClasses()]); 44 unsigned NumPSets = TRI->getNumRegPressureSets(); 45 PSetLimits.reset(new unsigned[NumPSets]); 46 std::fill(&PSetLimits[0], &PSetLimits[NumPSets], 0); 47 Update = true; 48 } 49 50 // Does this MF have different CSRs? 51 const MCPhysReg *CSR = TRI->getCalleeSavedRegs(MF); 52 if (Update || CSR != CalleeSaved) { 53 // Build a CSRNum map. Every CSR alias gets an entry pointing to the last 54 // overlapping CSR. 55 CSRNum.clear(); 56 CSRNum.resize(TRI->getNumRegs(), 0); 57 for (unsigned N = 0; unsigned Reg = CSR[N]; ++N) 58 for (MCRegAliasIterator AI(Reg, TRI, true); AI.isValid(); ++AI) 59 CSRNum[*AI] = N + 1; // 0 means no CSR, 1 means CalleeSaved[0], ... 60 Update = true; 61 } 62 CalleeSaved = CSR; 63 64 // Different reserved registers? 65 const BitVector &RR = MF->getRegInfo().getReservedRegs(); 66 if (Reserved.size() != RR.size() || RR != Reserved) { 67 Update = true; 68 Reserved = RR; 69 } 70 71 // Invalidate cached information from previous function. 72 if (Update) 73 ++Tag; 74 } 75 76 /// compute - Compute the preferred allocation order for RC with reserved 77 /// registers filtered out. Volatile registers come first followed by CSR 78 /// aliases ordered according to the CSR order specified by the target. 79 void RegisterClassInfo::compute(const TargetRegisterClass *RC) const { 80 RCInfo &RCI = RegClass[RC->getID()]; 81 82 // Raw register count, including all reserved regs. 83 unsigned NumRegs = RC->getNumRegs(); 84 85 if (!RCI.Order) 86 RCI.Order.reset(new MCPhysReg[NumRegs]); 87 88 unsigned N = 0; 89 SmallVector<MCPhysReg, 16> CSRAlias; 90 unsigned MinCost = 0xff; 91 unsigned LastCost = ~0u; 92 unsigned LastCostChange = 0; 93 94 // FIXME: Once targets reserve registers instead of removing them from the 95 // allocation order, we can simply use begin/end here. 96 ArrayRef<MCPhysReg> RawOrder = RC->getRawAllocationOrder(*MF); 97 for (unsigned i = 0; i != RawOrder.size(); ++i) { 98 unsigned PhysReg = RawOrder[i]; 99 // Remove reserved registers from the allocation order. 100 if (Reserved.test(PhysReg)) 101 continue; 102 unsigned Cost = TRI->getCostPerUse(PhysReg); 103 MinCost = std::min(MinCost, Cost); 104 105 if (CSRNum[PhysReg]) 106 // PhysReg aliases a CSR, save it for later. 107 CSRAlias.push_back(PhysReg); 108 else { 109 if (Cost != LastCost) 110 LastCostChange = N; 111 RCI.Order[N++] = PhysReg; 112 LastCost = Cost; 113 } 114 } 115 RCI.NumRegs = N + CSRAlias.size(); 116 assert (RCI.NumRegs <= NumRegs && "Allocation order larger than regclass"); 117 118 // CSR aliases go after the volatile registers, preserve the target's order. 119 for (unsigned i = 0, e = CSRAlias.size(); i != e; ++i) { 120 unsigned PhysReg = CSRAlias[i]; 121 unsigned Cost = TRI->getCostPerUse(PhysReg); 122 if (Cost != LastCost) 123 LastCostChange = N; 124 RCI.Order[N++] = PhysReg; 125 LastCost = Cost; 126 } 127 128 // Register allocator stress test. Clip register class to N registers. 129 if (StressRA && RCI.NumRegs > StressRA) 130 RCI.NumRegs = StressRA; 131 132 // Check if RC is a proper sub-class. 133 if (const TargetRegisterClass *Super = TRI->getLargestLegalSuperClass(RC)) 134 if (Super != RC && getNumAllocatableRegs(Super) > RCI.NumRegs) 135 RCI.ProperSubClass = true; 136 137 RCI.MinCost = uint8_t(MinCost); 138 RCI.LastCostChange = LastCostChange; 139 140 DEBUG({ 141 dbgs() << "AllocationOrder(" << RC->getName() << ") = ["; 142 for (unsigned I = 0; I != RCI.NumRegs; ++I) 143 dbgs() << ' ' << PrintReg(RCI.Order[I], TRI); 144 dbgs() << (RCI.ProperSubClass ? " ] (sub-class)\n" : " ]\n"); 145 }); 146 147 // RCI is now up-to-date. 148 RCI.Tag = Tag; 149 } 150 151 /// This is not accurate because two overlapping register sets may have some 152 /// nonoverlapping reserved registers. However, computing the allocation order 153 /// for all register classes would be too expensive. 154 unsigned RegisterClassInfo::computePSetLimit(unsigned Idx) const { 155 const TargetRegisterClass *RC = nullptr; 156 unsigned NumRCUnits = 0; 157 for (TargetRegisterInfo::regclass_iterator 158 RI = TRI->regclass_begin(), RE = TRI->regclass_end(); RI != RE; ++RI) { 159 const int *PSetID = TRI->getRegClassPressureSets(*RI); 160 for (; *PSetID != -1; ++PSetID) { 161 if ((unsigned)*PSetID == Idx) 162 break; 163 } 164 if (*PSetID == -1) 165 continue; 166 167 // Found a register class that counts against this pressure set. 168 // For efficiency, only compute the set order for the largest set. 169 unsigned NUnits = TRI->getRegClassWeight(*RI).WeightLimit; 170 if (!RC || NUnits > NumRCUnits) { 171 RC = *RI; 172 NumRCUnits = NUnits; 173 } 174 } 175 compute(RC); 176 unsigned NReserved = RC->getNumRegs() - getNumAllocatableRegs(RC); 177 return TRI->getRegPressureSetLimit(Idx) 178 - TRI->getRegClassWeight(RC).RegWeight * NReserved; 179 } 180