327 lines · cpp
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-exception6//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 22using namespace llvm;23 24bool 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 GlobalAddresses41 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 return false;49 }50 51 // Match Constants52 if (auto *A = dyn_cast<ConstantPoolSDNode>(Base)) {53 if (auto *B = dyn_cast<ConstantPoolSDNode>(Other.Base)) {54 bool IsMatch =55 A->isMachineConstantPoolEntry() == B->isMachineConstantPoolEntry();56 if (IsMatch) {57 if (A->isMachineConstantPoolEntry())58 IsMatch = A->getMachineCPVal() == B->getMachineCPVal();59 else60 IsMatch = A->getConstVal() == B->getConstVal();61 }62 if (IsMatch) {63 Off += B->getOffset() - A->getOffset();64 return true;65 }66 }67 68 return false;69 }70 71 // Match FrameIndexes.72 if (auto *A = dyn_cast<FrameIndexSDNode>(Base))73 if (auto *B = dyn_cast<FrameIndexSDNode>(Other.Base)) {74 // Equal FrameIndexes - offsets are directly comparable.75 if (A->getIndex() == B->getIndex())76 return true;77 // Non-equal FrameIndexes - If both frame indices are fixed78 // we know their relative offsets and can compare them. Otherwise79 // we must be conservative.80 const MachineFrameInfo &MFI = DAG.getMachineFunction().getFrameInfo();81 if (MFI.isFixedObjectIndex(A->getIndex()) &&82 MFI.isFixedObjectIndex(B->getIndex())) {83 Off += MFI.getObjectOffset(B->getIndex()) -84 MFI.getObjectOffset(A->getIndex());85 return true;86 }87 }88 }89 90 return false;91}92 93bool BaseIndexOffset::computeAliasing(const SDNode *Op0,94 const LocationSize NumBytes0,95 const SDNode *Op1,96 const LocationSize NumBytes1,97 const SelectionDAG &DAG, bool &IsAlias) {98 BaseIndexOffset BasePtr0 = match(Op0, DAG);99 if (!BasePtr0.getBase().getNode())100 return false;101 102 BaseIndexOffset BasePtr1 = match(Op1, DAG);103 if (!BasePtr1.getBase().getNode())104 return false;105 106 int64_t PtrDiff;107 if (BasePtr0.equalBaseIndex(BasePtr1, DAG, PtrDiff)) {108 // If the size of memory access is unknown, do not use it to analysis.109 // BasePtr1 is PtrDiff away from BasePtr0. They alias if none of the110 // following situations arise:111 if (PtrDiff >= 0 && NumBytes0.hasValue() && !NumBytes0.isScalable()) {112 // [----BasePtr0----]113 // [---BasePtr1--]114 // ========PtrDiff========>115 IsAlias = !(static_cast<int64_t>(NumBytes0.getValue().getFixedValue()) <=116 PtrDiff);117 return true;118 }119 if (PtrDiff < 0 && NumBytes1.hasValue() && !NumBytes1.isScalable()) {120 // [----BasePtr0----]121 // [---BasePtr1--]122 // =====(-PtrDiff)====>123 IsAlias = !((PtrDiff + static_cast<int64_t>(124 NumBytes1.getValue().getFixedValue())) <= 0);125 return true;126 }127 return false;128 }129 // If both BasePtr0 and BasePtr1 are FrameIndexes, we will not be130 // able to calculate their relative offset if at least one arises131 // from an alloca. However, these allocas cannot overlap and we132 // can infer there is no alias.133 if (auto *A = dyn_cast<FrameIndexSDNode>(BasePtr0.getBase()))134 if (auto *B = dyn_cast<FrameIndexSDNode>(BasePtr1.getBase())) {135 MachineFrameInfo &MFI = DAG.getMachineFunction().getFrameInfo();136 // If the base are the same frame index but the we couldn't find a137 // constant offset, (indices are different) be conservative.138 if (A->getIndex() != B->getIndex() && (!MFI.isFixedObjectIndex(A->getIndex()) ||139 !MFI.isFixedObjectIndex(B->getIndex()))) {140 IsAlias = false;141 return true;142 }143 }144 145 bool IsFI0 = isa<FrameIndexSDNode>(BasePtr0.getBase());146 bool IsFI1 = isa<FrameIndexSDNode>(BasePtr1.getBase());147 bool IsGV0 = isa<GlobalAddressSDNode>(BasePtr0.getBase());148 bool IsGV1 = isa<GlobalAddressSDNode>(BasePtr1.getBase());149 bool IsCV0 = isa<ConstantPoolSDNode>(BasePtr0.getBase());150 bool IsCV1 = isa<ConstantPoolSDNode>(BasePtr1.getBase());151 152 if ((IsFI0 || IsGV0 || IsCV0) && (IsFI1 || IsGV1 || IsCV1)) {153 // We can derive NoAlias In case of mismatched base types.154 if (IsFI0 != IsFI1 || IsGV0 != IsGV1 || IsCV0 != IsCV1) {155 IsAlias = false;156 return true;157 }158 if (IsGV0 && IsGV1) {159 auto *GV0 = cast<GlobalAddressSDNode>(BasePtr0.getBase())->getGlobal();160 auto *GV1 = cast<GlobalAddressSDNode>(BasePtr1.getBase())->getGlobal();161 // It doesn't make sense to access one global value using another globals162 // values address, so we can assume that there is no aliasing in case of163 // two different globals (unless we have symbols that may indirectly point164 // to each other).165 // FIXME: This is perhaps a bit too defensive. We could try to follow the166 // chain with aliasee information for GlobalAlias variables to find out if167 // we indirect symbols may alias or not.168 if (GV0 != GV1 && !isa<GlobalAlias>(GV0) && !isa<GlobalAlias>(GV1)) {169 IsAlias = false;170 return true;171 }172 }173 }174 return false; // Cannot determine whether the pointers alias.175}176 177bool BaseIndexOffset::contains(const SelectionDAG &DAG, int64_t BitSize,178 const BaseIndexOffset &Other,179 int64_t OtherBitSize, int64_t &BitOffset) const {180 int64_t Offset;181 if (!equalBaseIndex(Other, DAG, Offset))182 return false;183 if (Offset >= 0) {184 // Other is after *this:185 // [-------*this---------]186 // [---Other--]187 // ==Offset==>188 BitOffset = 8 * Offset;189 return BitOffset + OtherBitSize <= BitSize;190 }191 // Other starts strictly before *this, it cannot be fully contained.192 // [-------*this---------]193 // [--Other--]194 return false;195}196 197/// Parses tree in Ptr for base, index, offset addresses.198static BaseIndexOffset matchLSNode(const LSBaseSDNode *N,199 const SelectionDAG &DAG) {200 SDValue Ptr = N->getBasePtr();201 202 // (((B + I*M) + c)) + c ...203 SDValue Base = DAG.getTargetLoweringInfo().unwrapAddress(Ptr);204 SDValue Index = SDValue();205 int64_t Offset = 0;206 bool IsIndexSignExt = false;207 208 // pre-inc/pre-dec ops are components of EA.209 if (N->getAddressingMode() == ISD::PRE_INC) {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 } else if (N->getAddressingMode() == ISD::PRE_DEC) {215 if (auto *C = dyn_cast<ConstantSDNode>(N->getOffset()))216 Offset -= C->getSExtValue();217 else // If unknown, give up now.218 return BaseIndexOffset(SDValue(), SDValue(), 0, false);219 }220 221 // Consume constant adds & ors with appropriate masking.222 while (true) {223 switch (Base->getOpcode()) {224 case ISD::OR:225 // Only consider ORs which act as adds.226 if (auto *C = dyn_cast<ConstantSDNode>(Base->getOperand(1)))227 if (DAG.MaskedValueIsZero(Base->getOperand(0), C->getAPIntValue())) {228 Offset += C->getSExtValue();229 Base = DAG.getTargetLoweringInfo().unwrapAddress(Base->getOperand(0));230 continue;231 }232 break;233 case ISD::ADD:234 case ISD::PTRADD:235 if (auto *C = dyn_cast<ConstantSDNode>(Base->getOperand(1))) {236 Offset += C->getSExtValue();237 Base = DAG.getTargetLoweringInfo().unwrapAddress(Base->getOperand(0));238 continue;239 }240 break;241 case ISD::LOAD:242 case ISD::STORE: {243 auto *LSBase = cast<LSBaseSDNode>(Base.getNode());244 unsigned int IndexResNo = (Base->getOpcode() == ISD::LOAD) ? 1 : 0;245 if (LSBase->isIndexed() && Base.getResNo() == IndexResNo)246 if (auto *C = dyn_cast<ConstantSDNode>(LSBase->getOffset())) {247 auto Off = C->getSExtValue();248 if (LSBase->getAddressingMode() == ISD::PRE_DEC ||249 LSBase->getAddressingMode() == ISD::POST_DEC)250 Offset -= Off;251 else252 Offset += Off;253 Base = DAG.getTargetLoweringInfo().unwrapAddress(LSBase->getBasePtr());254 continue;255 }256 break;257 }258 }259 // If we get here break out of the loop.260 break;261 }262 263 if (Base->isAnyAdd()) {264 // TODO: The following code appears to be needless as it just265 // bails on some Ptrs early, reducing the cases where we266 // find equivalence. We should be able to remove this.267 // Inside a loop the current BASE pointer is calculated using an ADD and a268 // MUL instruction. In this case Base is the actual BASE pointer.269 // (i64 add (i64 %array_ptr)270 // (i64 mul (i64 %induction_var)271 // (i64 %element_size)))272 if (Base->getOperand(1)->getOpcode() == ISD::MUL)273 return BaseIndexOffset(Base, Index, Offset, IsIndexSignExt);274 275 // Look at Base + Index + Offset cases.276 Index = Base->getOperand(1);277 SDValue PotentialBase = Base->getOperand(0);278 279 // Skip signextends.280 if (Index->getOpcode() == ISD::SIGN_EXTEND) {281 Index = Index->getOperand(0);282 IsIndexSignExt = true;283 }284 285 // Check if Index Offset pattern286 if (!Index->isAnyAdd() || !isa<ConstantSDNode>(Index->getOperand(1)))287 return BaseIndexOffset(PotentialBase, Index, Offset, IsIndexSignExt);288 289 Offset += cast<ConstantSDNode>(Index->getOperand(1))->getSExtValue();290 Index = Index->getOperand(0);291 if (Index->getOpcode() == ISD::SIGN_EXTEND) {292 Index = Index->getOperand(0);293 IsIndexSignExt = true;294 } else295 IsIndexSignExt = false;296 Base = PotentialBase;297 }298 return BaseIndexOffset(Base, Index, Offset, IsIndexSignExt);299}300 301BaseIndexOffset BaseIndexOffset::match(const SDNode *N,302 const SelectionDAG &DAG) {303 if (const auto *LS0 = dyn_cast<LSBaseSDNode>(N))304 return matchLSNode(LS0, DAG);305 if (const auto *LN = dyn_cast<LifetimeSDNode>(N)) {306 return BaseIndexOffset(LN->getOperand(1), SDValue(), 0, false);307 }308 return BaseIndexOffset();309}310 311#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)312 313LLVM_DUMP_METHOD void BaseIndexOffset::dump() const {314 print(dbgs());315}316 317void BaseIndexOffset::print(raw_ostream& OS) const {318 OS << "BaseIndexOffset base=[";319 Base->print(OS);320 OS << "] index=[";321 if (Index)322 Index->print(OS);323 OS << "] offset=" << Offset;324}325 326#endif327