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/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.hasValue() && NumBytes1.hasValue() &&
 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