1 //==- llvm/CodeGen/SelectionDAGAddressAnalysis.cpp - DAG Address Analysis --==// 2 // 3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. 4 // See https://llvm.org/LICENSE.txt for license information. 5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception 6 // 7 //===----------------------------------------------------------------------===// 8 9 #include "llvm/CodeGen/SelectionDAGAddressAnalysis.h" 10 #include "llvm/Analysis/MemoryLocation.h" 11 #include "llvm/CodeGen/ISDOpcodes.h" 12 #include "llvm/CodeGen/MachineFrameInfo.h" 13 #include "llvm/CodeGen/MachineFunction.h" 14 #include "llvm/CodeGen/SelectionDAG.h" 15 #include "llvm/CodeGen/SelectionDAGNodes.h" 16 #include "llvm/CodeGen/TargetLowering.h" 17 #include "llvm/IR/GlobalAlias.h" 18 #include "llvm/Support/Casting.h" 19 #include "llvm/Support/Debug.h" 20 #include <cstdint> 21 22 using namespace llvm; 23 24 bool BaseIndexOffset::equalBaseIndex(const BaseIndexOffset &Other, 25 const SelectionDAG &DAG, 26 int64_t &Off) const { 27 // Conservatively fail if we a match failed.. 28 if (!Base.getNode() || !Other.Base.getNode()) 29 return false; 30 if (!hasValidOffset() || !Other.hasValidOffset()) 31 return false; 32 // Initial Offset difference. 33 Off = *Other.Offset - *Offset; 34 35 if ((Other.Index == Index) && (Other.IsIndexSignExt == IsIndexSignExt)) { 36 // Trivial match. 37 if (Other.Base == Base) 38 return true; 39 40 // Match GlobalAddresses 41 if (auto *A = dyn_cast<GlobalAddressSDNode>(Base)) 42 if (auto *B = dyn_cast<GlobalAddressSDNode>(Other.Base)) 43 if (A->getGlobal() == B->getGlobal()) { 44 Off += B->getOffset() - A->getOffset(); 45 return true; 46 } 47 48 // Match Constants 49 if (auto *A = dyn_cast<ConstantPoolSDNode>(Base)) 50 if (auto *B = dyn_cast<ConstantPoolSDNode>(Other.Base)) { 51 bool IsMatch = 52 A->isMachineConstantPoolEntry() == B->isMachineConstantPoolEntry(); 53 if (IsMatch) { 54 if (A->isMachineConstantPoolEntry()) 55 IsMatch = A->getMachineCPVal() == B->getMachineCPVal(); 56 else 57 IsMatch = A->getConstVal() == B->getConstVal(); 58 } 59 if (IsMatch) { 60 Off += B->getOffset() - A->getOffset(); 61 return true; 62 } 63 } 64 65 const MachineFrameInfo &MFI = DAG.getMachineFunction().getFrameInfo(); 66 67 // Match FrameIndexes. 68 if (auto *A = dyn_cast<FrameIndexSDNode>(Base)) 69 if (auto *B = dyn_cast<FrameIndexSDNode>(Other.Base)) { 70 // Equal FrameIndexes - offsets are directly comparable. 71 if (A->getIndex() == B->getIndex()) 72 return true; 73 // Non-equal FrameIndexes - If both frame indices are fixed 74 // we know their relative offsets and can compare them. Otherwise 75 // we must be conservative. 76 if (MFI.isFixedObjectIndex(A->getIndex()) && 77 MFI.isFixedObjectIndex(B->getIndex())) { 78 Off += MFI.getObjectOffset(B->getIndex()) - 79 MFI.getObjectOffset(A->getIndex()); 80 return true; 81 } 82 } 83 } 84 return false; 85 } 86 87 bool BaseIndexOffset::computeAliasing(const SDNode *Op0, 88 const Optional<int64_t> NumBytes0, 89 const SDNode *Op1, 90 const Optional<int64_t> NumBytes1, 91 const SelectionDAG &DAG, bool &IsAlias) { 92 93 BaseIndexOffset BasePtr0 = match(Op0, DAG); 94 BaseIndexOffset BasePtr1 = match(Op1, DAG); 95 96 if (!(BasePtr0.getBase().getNode() && BasePtr1.getBase().getNode())) 97 return false; 98 int64_t PtrDiff; 99 if (NumBytes0 && NumBytes1 && 100 BasePtr0.equalBaseIndex(BasePtr1, DAG, PtrDiff)) { 101 // If the size of memory access is unknown, do not use it to analysis. 102 // One example of unknown size memory access is to load/store scalable 103 // vector objects on the stack. 104 // BasePtr1 is PtrDiff away from BasePtr0. They alias if none of the 105 // following situations arise: 106 if (PtrDiff >= 0 && 107 *NumBytes0 != static_cast<int64_t>(MemoryLocation::UnknownSize)) { 108 // [----BasePtr0----] 109 // [---BasePtr1--] 110 // ========PtrDiff========> 111 IsAlias = !(*NumBytes0 <= PtrDiff); 112 return true; 113 } 114 if (PtrDiff < 0 && 115 *NumBytes1 != static_cast<int64_t>(MemoryLocation::UnknownSize)) { 116 // [----BasePtr0----] 117 // [---BasePtr1--] 118 // =====(-PtrDiff)====> 119 IsAlias = !((PtrDiff + *NumBytes1) <= 0); 120 return true; 121 } 122 return false; 123 } 124 // If both BasePtr0 and BasePtr1 are FrameIndexes, we will not be 125 // able to calculate their relative offset if at least one arises 126 // from an alloca. However, these allocas cannot overlap and we 127 // can infer there is no alias. 128 if (auto *A = dyn_cast<FrameIndexSDNode>(BasePtr0.getBase())) 129 if (auto *B = dyn_cast<FrameIndexSDNode>(BasePtr1.getBase())) { 130 MachineFrameInfo &MFI = DAG.getMachineFunction().getFrameInfo(); 131 // If the base are the same frame index but the we couldn't find a 132 // constant offset, (indices are different) be conservative. 133 if (A != B && (!MFI.isFixedObjectIndex(A->getIndex()) || 134 !MFI.isFixedObjectIndex(B->getIndex()))) { 135 IsAlias = false; 136 return true; 137 } 138 } 139 140 bool IsFI0 = isa<FrameIndexSDNode>(BasePtr0.getBase()); 141 bool IsFI1 = isa<FrameIndexSDNode>(BasePtr1.getBase()); 142 bool IsGV0 = isa<GlobalAddressSDNode>(BasePtr0.getBase()); 143 bool IsGV1 = isa<GlobalAddressSDNode>(BasePtr1.getBase()); 144 bool IsCV0 = isa<ConstantPoolSDNode>(BasePtr0.getBase()); 145 bool IsCV1 = isa<ConstantPoolSDNode>(BasePtr1.getBase()); 146 147 if ((IsFI0 || IsGV0 || IsCV0) && (IsFI1 || IsGV1 || IsCV1)) { 148 // We can derive NoAlias In case of mismatched base types. 149 if (IsFI0 != IsFI1 || IsGV0 != IsGV1 || IsCV0 != IsCV1) { 150 IsAlias = false; 151 return true; 152 } 153 if (IsGV0 && IsGV1) { 154 auto *GV0 = cast<GlobalAddressSDNode>(BasePtr0.getBase())->getGlobal(); 155 auto *GV1 = cast<GlobalAddressSDNode>(BasePtr1.getBase())->getGlobal(); 156 // It doesn't make sense to access one global value using another globals 157 // values address, so we can assume that there is no aliasing in case of 158 // two different globals (unless we have symbols that may indirectly point 159 // to each other). 160 // FIXME: This is perhaps a bit too defensive. We could try to follow the 161 // chain with aliasee information for GlobalAlias variables to find out if 162 // we indirect symbols may alias or not. 163 if (GV0 != GV1 && !isa<GlobalAlias>(GV0) && !isa<GlobalAlias>(GV1)) { 164 IsAlias = false; 165 return true; 166 } 167 } 168 } 169 return false; // Cannot determine whether the pointers alias. 170 } 171 172 bool BaseIndexOffset::contains(const SelectionDAG &DAG, int64_t BitSize, 173 const BaseIndexOffset &Other, 174 int64_t OtherBitSize, int64_t &BitOffset) const { 175 int64_t Offset; 176 if (!equalBaseIndex(Other, DAG, Offset)) 177 return false; 178 if (Offset >= 0) { 179 // Other is after *this: 180 // [-------*this---------] 181 // [---Other--] 182 // ==Offset==> 183 BitOffset = 8 * Offset; 184 return BitOffset + OtherBitSize <= BitSize; 185 } 186 // Other starts strictly before *this, it cannot be fully contained. 187 // [-------*this---------] 188 // [--Other--] 189 return false; 190 } 191 192 /// Parses tree in Ptr for base, index, offset addresses. 193 static BaseIndexOffset matchLSNode(const LSBaseSDNode *N, 194 const SelectionDAG &DAG) { 195 SDValue Ptr = N->getBasePtr(); 196 197 // (((B + I*M) + c)) + c ... 198 SDValue Base = DAG.getTargetLoweringInfo().unwrapAddress(Ptr); 199 SDValue Index = SDValue(); 200 int64_t Offset = 0; 201 bool IsIndexSignExt = false; 202 203 // pre-inc/pre-dec ops are components of EA. 204 if (N->getAddressingMode() == ISD::PRE_INC) { 205 if (auto *C = dyn_cast<ConstantSDNode>(N->getOffset())) 206 Offset += C->getSExtValue(); 207 else // If unknown, give up now. 208 return BaseIndexOffset(SDValue(), SDValue(), 0, false); 209 } else if (N->getAddressingMode() == ISD::PRE_DEC) { 210 if (auto *C = dyn_cast<ConstantSDNode>(N->getOffset())) 211 Offset -= C->getSExtValue(); 212 else // If unknown, give up now. 213 return BaseIndexOffset(SDValue(), SDValue(), 0, false); 214 } 215 216 // Consume constant adds & ors with appropriate masking. 217 while (true) { 218 switch (Base->getOpcode()) { 219 case ISD::OR: 220 // Only consider ORs which act as adds. 221 if (auto *C = dyn_cast<ConstantSDNode>(Base->getOperand(1))) 222 if (DAG.MaskedValueIsZero(Base->getOperand(0), C->getAPIntValue())) { 223 Offset += C->getSExtValue(); 224 Base = DAG.getTargetLoweringInfo().unwrapAddress(Base->getOperand(0)); 225 continue; 226 } 227 break; 228 case ISD::ADD: 229 if (auto *C = dyn_cast<ConstantSDNode>(Base->getOperand(1))) { 230 Offset += C->getSExtValue(); 231 Base = DAG.getTargetLoweringInfo().unwrapAddress(Base->getOperand(0)); 232 continue; 233 } 234 break; 235 case ISD::LOAD: 236 case ISD::STORE: { 237 auto *LSBase = cast<LSBaseSDNode>(Base.getNode()); 238 unsigned int IndexResNo = (Base->getOpcode() == ISD::LOAD) ? 1 : 0; 239 if (LSBase->isIndexed() && Base.getResNo() == IndexResNo) 240 if (auto *C = dyn_cast<ConstantSDNode>(LSBase->getOffset())) { 241 auto Off = C->getSExtValue(); 242 if (LSBase->getAddressingMode() == ISD::PRE_DEC || 243 LSBase->getAddressingMode() == ISD::POST_DEC) 244 Offset -= Off; 245 else 246 Offset += Off; 247 Base = DAG.getTargetLoweringInfo().unwrapAddress(LSBase->getBasePtr()); 248 continue; 249 } 250 break; 251 } 252 } 253 // If we get here break out of the loop. 254 break; 255 } 256 257 if (Base->getOpcode() == ISD::ADD) { 258 // TODO: The following code appears to be needless as it just 259 // bails on some Ptrs early, reducing the cases where we 260 // find equivalence. We should be able to remove this. 261 // Inside a loop the current BASE pointer is calculated using an ADD and a 262 // MUL instruction. In this case Base is the actual BASE pointer. 263 // (i64 add (i64 %array_ptr) 264 // (i64 mul (i64 %induction_var) 265 // (i64 %element_size))) 266 if (Base->getOperand(1)->getOpcode() == ISD::MUL) 267 return BaseIndexOffset(Base, Index, Offset, IsIndexSignExt); 268 269 // Look at Base + Index + Offset cases. 270 Index = Base->getOperand(1); 271 SDValue PotentialBase = Base->getOperand(0); 272 273 // Skip signextends. 274 if (Index->getOpcode() == ISD::SIGN_EXTEND) { 275 Index = Index->getOperand(0); 276 IsIndexSignExt = true; 277 } 278 279 // Check if Index Offset pattern 280 if (Index->getOpcode() != ISD::ADD || 281 !isa<ConstantSDNode>(Index->getOperand(1))) 282 return BaseIndexOffset(PotentialBase, Index, Offset, IsIndexSignExt); 283 284 Offset += cast<ConstantSDNode>(Index->getOperand(1))->getSExtValue(); 285 Index = Index->getOperand(0); 286 if (Index->getOpcode() == ISD::SIGN_EXTEND) { 287 Index = Index->getOperand(0); 288 IsIndexSignExt = true; 289 } else 290 IsIndexSignExt = false; 291 Base = PotentialBase; 292 } 293 return BaseIndexOffset(Base, Index, Offset, IsIndexSignExt); 294 } 295 296 BaseIndexOffset BaseIndexOffset::match(const SDNode *N, 297 const SelectionDAG &DAG) { 298 if (const auto *LS0 = dyn_cast<LSBaseSDNode>(N)) 299 return matchLSNode(LS0, DAG); 300 if (const auto *LN = dyn_cast<LifetimeSDNode>(N)) { 301 if (LN->hasOffset()) 302 return BaseIndexOffset(LN->getOperand(1), SDValue(), LN->getOffset(), 303 false); 304 return BaseIndexOffset(LN->getOperand(1), SDValue(), false); 305 } 306 return BaseIndexOffset(); 307 } 308 309 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP) 310 311 LLVM_DUMP_METHOD void BaseIndexOffset::dump() const { 312 print(dbgs()); 313 } 314 315 void BaseIndexOffset::print(raw_ostream& OS) const { 316 OS << "BaseIndexOffset base=["; 317 Base->print(OS); 318 OS << "] index=["; 319 if (Index) 320 Index->print(OS); 321 OS << "] offset=" << Offset; 322 } 323 324 #endif 325