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, const SelectionDAG &DAG,
140                                int64_t &Offset) const {
141   if (!equalBaseIndex(Other, DAG, Offset))
142     return false;
143   if (Offset >= 0) {
144     // Other is after *this:
145     // [-------*this---------]
146     //            [---Other--]
147     // ==Offset==>
148     return Offset + OtherSize <= Size;
149   }
150   // Other starts strictly before *this, it cannot be fully contained.
151   //    [-------*this---------]
152   // [--Other--]
153   return false;
154 }
155 
156 /// Parses tree in Ptr for base, index, offset addresses.
157 BaseIndexOffset BaseIndexOffset::match(const LSBaseSDNode *N,
158                                        const SelectionDAG &DAG) {
159   SDValue Ptr = N->getBasePtr();
160 
161   // (((B + I*M) + c)) + c ...
162   SDValue Base = DAG.getTargetLoweringInfo().unwrapAddress(Ptr);
163   SDValue Index = SDValue();
164   int64_t Offset = 0;
165   bool IsIndexSignExt = false;
166 
167   // pre-inc/pre-dec ops are components of EA.
168   if (N->getAddressingMode() == ISD::PRE_INC) {
169     if (auto *C = dyn_cast<ConstantSDNode>(N->getOffset()))
170       Offset += C->getSExtValue();
171     else // If unknown, give up now.
172       return BaseIndexOffset(SDValue(), SDValue(), 0, false);
173   } else if (N->getAddressingMode() == ISD::PRE_DEC) {
174     if (auto *C = dyn_cast<ConstantSDNode>(N->getOffset()))
175       Offset -= C->getSExtValue();
176     else // If unknown, give up now.
177       return BaseIndexOffset(SDValue(), SDValue(), 0, false);
178   }
179 
180   // Consume constant adds & ors with appropriate masking.
181   while (true) {
182     switch (Base->getOpcode()) {
183     case ISD::OR:
184       // Only consider ORs which act as adds.
185       if (auto *C = dyn_cast<ConstantSDNode>(Base->getOperand(1)))
186         if (DAG.MaskedValueIsZero(Base->getOperand(0), C->getAPIntValue())) {
187           Offset += C->getSExtValue();
188           Base = DAG.getTargetLoweringInfo().unwrapAddress(Base->getOperand(0));
189           continue;
190         }
191       break;
192     case ISD::ADD:
193       if (auto *C = dyn_cast<ConstantSDNode>(Base->getOperand(1))) {
194         Offset += C->getSExtValue();
195         Base = DAG.getTargetLoweringInfo().unwrapAddress(Base->getOperand(0));
196         continue;
197       }
198       break;
199     case ISD::LOAD:
200     case ISD::STORE: {
201       auto *LSBase = cast<LSBaseSDNode>(Base.getNode());
202       unsigned int IndexResNo = (Base->getOpcode() == ISD::LOAD) ? 1 : 0;
203       if (LSBase->isIndexed() && Base.getResNo() == IndexResNo)
204         if (auto *C = dyn_cast<ConstantSDNode>(LSBase->getOffset())) {
205           auto Off = C->getSExtValue();
206           if (LSBase->getAddressingMode() == ISD::PRE_DEC ||
207               LSBase->getAddressingMode() == ISD::POST_DEC)
208             Offset -= Off;
209           else
210             Offset += Off;
211           Base = DAG.getTargetLoweringInfo().unwrapAddress(LSBase->getBasePtr());
212           continue;
213         }
214       break;
215     }
216     }
217     // If we get here break out of the loop.
218     break;
219   }
220 
221   if (Base->getOpcode() == ISD::ADD) {
222     // TODO: The following code appears to be needless as it just
223     //       bails on some Ptrs early, reducing the cases where we
224     //       find equivalence. We should be able to remove this.
225     // Inside a loop the current BASE pointer is calculated using an ADD and a
226     // MUL instruction. In this case Base is the actual BASE pointer.
227     // (i64 add (i64 %array_ptr)
228     //          (i64 mul (i64 %induction_var)
229     //                   (i64 %element_size)))
230     if (Base->getOperand(1)->getOpcode() == ISD::MUL)
231       return BaseIndexOffset(Base, Index, Offset, IsIndexSignExt);
232 
233     // Look at Base + Index + Offset cases.
234     Index = Base->getOperand(1);
235     SDValue PotentialBase = Base->getOperand(0);
236 
237     // Skip signextends.
238     if (Index->getOpcode() == ISD::SIGN_EXTEND) {
239       Index = Index->getOperand(0);
240       IsIndexSignExt = true;
241     }
242 
243     // Check if Index Offset pattern
244     if (Index->getOpcode() != ISD::ADD ||
245         !isa<ConstantSDNode>(Index->getOperand(1)))
246       return BaseIndexOffset(PotentialBase, Index, Offset, IsIndexSignExt);
247 
248     Offset += cast<ConstantSDNode>(Index->getOperand(1))->getSExtValue();
249     Index = Index->getOperand(0);
250     if (Index->getOpcode() == ISD::SIGN_EXTEND) {
251       Index = Index->getOperand(0);
252       IsIndexSignExt = true;
253     } else
254       IsIndexSignExt = false;
255     Base = PotentialBase;
256   }
257   return BaseIndexOffset(Base, Index, Offset, IsIndexSignExt);
258 }
259 
260 
261 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
262 
263 LLVM_DUMP_METHOD void BaseIndexOffset::dump() const {
264   print(dbgs());
265 }
266 
267 void BaseIndexOffset::print(raw_ostream& OS) const {
268   OS << "BaseIndexOffset base=[";
269   Base->print(OS);
270   OS << "] index=[";
271   if (Index)
272     Index->print(OS);
273   OS << "] offset=" << Offset;
274 }
275 
276 #endif
277