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