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