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