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 
22 using namespace llvm;
23 
equalBaseIndex(const BaseIndexOffset & Other,const SelectionDAG & DAG,int64_t & Off) const24 bool 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       return false;
49     }
50 
51     // Match Constants
52     if (auto *A = dyn_cast<ConstantPoolSDNode>(Base)) {
53       if (auto *B = dyn_cast<ConstantPoolSDNode>(Other.Base)) {
54         bool IsMatch =
55             A->isMachineConstantPoolEntry() == B->isMachineConstantPoolEntry();
56         if (IsMatch) {
57           if (A->isMachineConstantPoolEntry())
58             IsMatch = A->getMachineCPVal() == B->getMachineCPVal();
59           else
60             IsMatch = A->getConstVal() == B->getConstVal();
61         }
62         if (IsMatch) {
63           Off += B->getOffset() - A->getOffset();
64           return true;
65         }
66       }
67 
68       return false;
69     }
70 
71     // Match FrameIndexes.
72     if (auto *A = dyn_cast<FrameIndexSDNode>(Base))
73       if (auto *B = dyn_cast<FrameIndexSDNode>(Other.Base)) {
74         // Equal FrameIndexes - offsets are directly comparable.
75         if (A->getIndex() == B->getIndex())
76           return true;
77         // Non-equal FrameIndexes - If both frame indices are fixed
78         // we know their relative offsets and can compare them. Otherwise
79         // we must be conservative.
80         const MachineFrameInfo &MFI = DAG.getMachineFunction().getFrameInfo();
81         if (MFI.isFixedObjectIndex(A->getIndex()) &&
82             MFI.isFixedObjectIndex(B->getIndex())) {
83           Off += MFI.getObjectOffset(B->getIndex()) -
84                  MFI.getObjectOffset(A->getIndex());
85           return true;
86         }
87       }
88   }
89 
90   return false;
91 }
92 
computeAliasing(const SDNode * Op0,const std::optional<int64_t> NumBytes0,const SDNode * Op1,const std::optional<int64_t> NumBytes1,const SelectionDAG & DAG,bool & IsAlias)93 bool BaseIndexOffset::computeAliasing(const SDNode *Op0,
94                                       const std::optional<int64_t> NumBytes0,
95                                       const SDNode *Op1,
96                                       const std::optional<int64_t> NumBytes1,
97                                       const SelectionDAG &DAG, bool &IsAlias) {
98 
99   BaseIndexOffset BasePtr0 = match(Op0, DAG);
100   if (!BasePtr0.getBase().getNode())
101     return false;
102 
103   BaseIndexOffset BasePtr1 = match(Op1, DAG);
104   if (!BasePtr1.getBase().getNode())
105     return false;
106 
107   int64_t PtrDiff;
108   if (NumBytes0 && NumBytes1 &&
109       BasePtr0.equalBaseIndex(BasePtr1, DAG, PtrDiff)) {
110     // If the size of memory access is unknown, do not use it to analysis.
111     // One example of unknown size memory access is to load/store scalable
112     // vector objects on the stack.
113     // BasePtr1 is PtrDiff away from BasePtr0. They alias if none of the
114     // following situations arise:
115     if (PtrDiff >= 0 &&
116         *NumBytes0 != static_cast<int64_t>(MemoryLocation::UnknownSize)) {
117       // [----BasePtr0----]
118       //                         [---BasePtr1--]
119       // ========PtrDiff========>
120       IsAlias = !(*NumBytes0 <= PtrDiff);
121       return true;
122     }
123     if (PtrDiff < 0 &&
124         *NumBytes1 != static_cast<int64_t>(MemoryLocation::UnknownSize)) {
125       //                     [----BasePtr0----]
126       // [---BasePtr1--]
127       // =====(-PtrDiff)====>
128       IsAlias = !((PtrDiff + *NumBytes1) <= 0);
129       return true;
130     }
131     return false;
132   }
133   // If both BasePtr0 and BasePtr1 are FrameIndexes, we will not be
134   // able to calculate their relative offset if at least one arises
135   // from an alloca. However, these allocas cannot overlap and we
136   // can infer there is no alias.
137   if (auto *A = dyn_cast<FrameIndexSDNode>(BasePtr0.getBase()))
138     if (auto *B = dyn_cast<FrameIndexSDNode>(BasePtr1.getBase())) {
139       MachineFrameInfo &MFI = DAG.getMachineFunction().getFrameInfo();
140       // If the base are the same frame index but the we couldn't find a
141       // constant offset, (indices are different) be conservative.
142       if (A->getIndex() != B->getIndex() && (!MFI.isFixedObjectIndex(A->getIndex()) ||
143                      !MFI.isFixedObjectIndex(B->getIndex()))) {
144         IsAlias = false;
145         return true;
146       }
147     }
148 
149   bool IsFI0 = isa<FrameIndexSDNode>(BasePtr0.getBase());
150   bool IsFI1 = isa<FrameIndexSDNode>(BasePtr1.getBase());
151   bool IsGV0 = isa<GlobalAddressSDNode>(BasePtr0.getBase());
152   bool IsGV1 = isa<GlobalAddressSDNode>(BasePtr1.getBase());
153   bool IsCV0 = isa<ConstantPoolSDNode>(BasePtr0.getBase());
154   bool IsCV1 = isa<ConstantPoolSDNode>(BasePtr1.getBase());
155 
156   if ((IsFI0 || IsGV0 || IsCV0) && (IsFI1 || IsGV1 || IsCV1)) {
157     // We can derive NoAlias In case of mismatched base types.
158     if (IsFI0 != IsFI1 || IsGV0 != IsGV1 || IsCV0 != IsCV1) {
159       IsAlias = false;
160       return true;
161     }
162     if (IsGV0 && IsGV1) {
163       auto *GV0 = cast<GlobalAddressSDNode>(BasePtr0.getBase())->getGlobal();
164       auto *GV1 = cast<GlobalAddressSDNode>(BasePtr1.getBase())->getGlobal();
165       // It doesn't make sense to access one global value using another globals
166       // values address, so we can assume that there is no aliasing in case of
167       // two different globals (unless we have symbols that may indirectly point
168       // to each other).
169       // FIXME: This is perhaps a bit too defensive. We could try to follow the
170       // chain with aliasee information for GlobalAlias variables to find out if
171       // we indirect symbols may alias or not.
172       if (GV0 != GV1 && !isa<GlobalAlias>(GV0) && !isa<GlobalAlias>(GV1)) {
173         IsAlias = false;
174         return true;
175       }
176     }
177   }
178   return false; // Cannot determine whether the pointers alias.
179 }
180 
contains(const SelectionDAG & DAG,int64_t BitSize,const BaseIndexOffset & Other,int64_t OtherBitSize,int64_t & BitOffset) const181 bool BaseIndexOffset::contains(const SelectionDAG &DAG, int64_t BitSize,
182                                const BaseIndexOffset &Other,
183                                int64_t OtherBitSize, int64_t &BitOffset) const {
184   int64_t Offset;
185   if (!equalBaseIndex(Other, DAG, Offset))
186     return false;
187   if (Offset >= 0) {
188     // Other is after *this:
189     // [-------*this---------]
190     //            [---Other--]
191     // ==Offset==>
192     BitOffset = 8 * Offset;
193     return BitOffset + OtherBitSize <= BitSize;
194   }
195   // Other starts strictly before *this, it cannot be fully contained.
196   //    [-------*this---------]
197   // [--Other--]
198   return false;
199 }
200 
201 /// Parses tree in Ptr for base, index, offset addresses.
matchLSNode(const LSBaseSDNode * N,const SelectionDAG & DAG)202 static BaseIndexOffset matchLSNode(const LSBaseSDNode *N,
203                                    const SelectionDAG &DAG) {
204   SDValue Ptr = N->getBasePtr();
205 
206   // (((B + I*M) + c)) + c ...
207   SDValue Base = DAG.getTargetLoweringInfo().unwrapAddress(Ptr);
208   SDValue Index = SDValue();
209   int64_t Offset = 0;
210   bool IsIndexSignExt = false;
211 
212   // pre-inc/pre-dec ops are components of EA.
213   if (N->getAddressingMode() == ISD::PRE_INC) {
214     if (auto *C = dyn_cast<ConstantSDNode>(N->getOffset()))
215       Offset += C->getSExtValue();
216     else // If unknown, give up now.
217       return BaseIndexOffset(SDValue(), SDValue(), 0, false);
218   } else if (N->getAddressingMode() == ISD::PRE_DEC) {
219     if (auto *C = dyn_cast<ConstantSDNode>(N->getOffset()))
220       Offset -= C->getSExtValue();
221     else // If unknown, give up now.
222       return BaseIndexOffset(SDValue(), SDValue(), 0, false);
223   }
224 
225   // Consume constant adds & ors with appropriate masking.
226   while (true) {
227     switch (Base->getOpcode()) {
228     case ISD::OR:
229       // Only consider ORs which act as adds.
230       if (auto *C = dyn_cast<ConstantSDNode>(Base->getOperand(1)))
231         if (DAG.MaskedValueIsZero(Base->getOperand(0), C->getAPIntValue())) {
232           Offset += C->getSExtValue();
233           Base = DAG.getTargetLoweringInfo().unwrapAddress(Base->getOperand(0));
234           continue;
235         }
236       break;
237     case ISD::ADD:
238       if (auto *C = dyn_cast<ConstantSDNode>(Base->getOperand(1))) {
239         Offset += C->getSExtValue();
240         Base = DAG.getTargetLoweringInfo().unwrapAddress(Base->getOperand(0));
241         continue;
242       }
243       break;
244     case ISD::LOAD:
245     case ISD::STORE: {
246       auto *LSBase = cast<LSBaseSDNode>(Base.getNode());
247       unsigned int IndexResNo = (Base->getOpcode() == ISD::LOAD) ? 1 : 0;
248       if (LSBase->isIndexed() && Base.getResNo() == IndexResNo)
249         if (auto *C = dyn_cast<ConstantSDNode>(LSBase->getOffset())) {
250           auto Off = C->getSExtValue();
251           if (LSBase->getAddressingMode() == ISD::PRE_DEC ||
252               LSBase->getAddressingMode() == ISD::POST_DEC)
253             Offset -= Off;
254           else
255             Offset += Off;
256           Base = DAG.getTargetLoweringInfo().unwrapAddress(LSBase->getBasePtr());
257           continue;
258         }
259       break;
260     }
261     }
262     // If we get here break out of the loop.
263     break;
264   }
265 
266   if (Base->getOpcode() == ISD::ADD) {
267     // TODO: The following code appears to be needless as it just
268     //       bails on some Ptrs early, reducing the cases where we
269     //       find equivalence. We should be able to remove this.
270     // Inside a loop the current BASE pointer is calculated using an ADD and a
271     // MUL instruction. In this case Base is the actual BASE pointer.
272     // (i64 add (i64 %array_ptr)
273     //          (i64 mul (i64 %induction_var)
274     //                   (i64 %element_size)))
275     if (Base->getOperand(1)->getOpcode() == ISD::MUL)
276       return BaseIndexOffset(Base, Index, Offset, IsIndexSignExt);
277 
278     // Look at Base + Index + Offset cases.
279     Index = Base->getOperand(1);
280     SDValue PotentialBase = Base->getOperand(0);
281 
282     // Skip signextends.
283     if (Index->getOpcode() == ISD::SIGN_EXTEND) {
284       Index = Index->getOperand(0);
285       IsIndexSignExt = true;
286     }
287 
288     // Check if Index Offset pattern
289     if (Index->getOpcode() != ISD::ADD ||
290         !isa<ConstantSDNode>(Index->getOperand(1)))
291       return BaseIndexOffset(PotentialBase, Index, Offset, IsIndexSignExt);
292 
293     Offset += cast<ConstantSDNode>(Index->getOperand(1))->getSExtValue();
294     Index = Index->getOperand(0);
295     if (Index->getOpcode() == ISD::SIGN_EXTEND) {
296       Index = Index->getOperand(0);
297       IsIndexSignExt = true;
298     } else
299       IsIndexSignExt = false;
300     Base = PotentialBase;
301   }
302   return BaseIndexOffset(Base, Index, Offset, IsIndexSignExt);
303 }
304 
match(const SDNode * N,const SelectionDAG & DAG)305 BaseIndexOffset BaseIndexOffset::match(const SDNode *N,
306                                        const SelectionDAG &DAG) {
307   if (const auto *LS0 = dyn_cast<LSBaseSDNode>(N))
308     return matchLSNode(LS0, DAG);
309   if (const auto *LN = dyn_cast<LifetimeSDNode>(N)) {
310     if (LN->hasOffset())
311       return BaseIndexOffset(LN->getOperand(1), SDValue(), LN->getOffset(),
312                              false);
313     return BaseIndexOffset(LN->getOperand(1), SDValue(), false);
314   }
315   return BaseIndexOffset();
316 }
317 
318 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
319 
dump() const320 LLVM_DUMP_METHOD void BaseIndexOffset::dump() const {
321   print(dbgs());
322 }
323 
print(raw_ostream & OS) const324 void BaseIndexOffset::print(raw_ostream& OS) const {
325   OS << "BaseIndexOffset base=[";
326   Base->print(OS);
327   OS << "] index=[";
328   if (Index)
329     Index->print(OS);
330   OS << "] offset=" << Offset;
331 }
332 
333 #endif
334