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
20using namespace llvm;
21
22bool 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
85bool 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
146bool 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.
167static 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
270BaseIndexOffset 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
285LLVM_DUMP_METHOD void BaseIndexOffset::dump() const {
286  print(dbgs());
287}
288
289void 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
299