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