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
22using namespace llvm;
23
24bool 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
87bool BaseIndexOffset::computeAliasing(const SDNode *Op0,
88                                      const std::optional<int64_t> NumBytes0,
89                                      const SDNode *Op1,
90                                      const std::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 && NumBytes1 &&
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
172bool 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.
193static 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
296BaseIndexOffset 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
311LLVM_DUMP_METHOD void BaseIndexOffset::dump() const {
312  print(dbgs());
313}
314
315void 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
325