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>(Val: Base)) {
42 if (auto *B = dyn_cast<GlobalAddressSDNode>(Val: 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>(Val: Base)) {
53 if (auto *B = dyn_cast<ConstantPoolSDNode>(Val: 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>(Val: Base))
73 if (auto *B = dyn_cast<FrameIndexSDNode>(Val: 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(ObjectIdx: A->getIndex()) &&
82 MFI.isFixedObjectIndex(ObjectIdx: B->getIndex())) {
83 Off += MFI.getObjectOffset(ObjectIdx: B->getIndex()) -
84 MFI.getObjectOffset(ObjectIdx: A->getIndex());
85 return true;
86 }
87 }
88 }
89
90 return false;
91}
92
93bool BaseIndexOffset::computeAliasing(const SDNode *Op0,
94 const LocationSize NumBytes0,
95 const SDNode *Op1,
96 const LocationSize NumBytes1,
97 const SelectionDAG &DAG, bool &IsAlias) {
98 BaseIndexOffset BasePtr0 = match(N: Op0, DAG);
99 if (!BasePtr0.getBase().getNode())
100 return false;
101
102 BaseIndexOffset BasePtr1 = match(N: Op1, DAG);
103 if (!BasePtr1.getBase().getNode())
104 return false;
105
106 int64_t PtrDiff;
107 if (BasePtr0.equalBaseIndex(Other: BasePtr1, DAG, Off&: PtrDiff)) {
108 // If the size of memory access is unknown, do not use it to analysis.
109 // BasePtr1 is PtrDiff away from BasePtr0. They alias if none of the
110 // following situations arise:
111 if (PtrDiff >= 0 && NumBytes0.hasValue() && !NumBytes0.isScalable()) {
112 // [----BasePtr0----]
113 // [---BasePtr1--]
114 // ========PtrDiff========>
115 IsAlias = !(static_cast<int64_t>(NumBytes0.getValue().getFixedValue()) <=
116 PtrDiff);
117 return true;
118 }
119 if (PtrDiff < 0 && NumBytes1.hasValue() && !NumBytes1.isScalable()) {
120 // [----BasePtr0----]
121 // [---BasePtr1--]
122 // =====(-PtrDiff)====>
123 IsAlias = !((PtrDiff + static_cast<int64_t>(
124 NumBytes1.getValue().getFixedValue())) <= 0);
125 return true;
126 }
127 return false;
128 }
129 // If both BasePtr0 and BasePtr1 are FrameIndexes, we will not be
130 // able to calculate their relative offset if at least one arises
131 // from an alloca. However, these allocas cannot overlap and we
132 // can infer there is no alias.
133 if (auto *A = dyn_cast<FrameIndexSDNode>(Val: BasePtr0.getBase()))
134 if (auto *B = dyn_cast<FrameIndexSDNode>(Val: BasePtr1.getBase())) {
135 MachineFrameInfo &MFI = DAG.getMachineFunction().getFrameInfo();
136 // If the base are the same frame index but the we couldn't find a
137 // constant offset, (indices are different) be conservative.
138 if (A->getIndex() != B->getIndex() && (!MFI.isFixedObjectIndex(ObjectIdx: A->getIndex()) ||
139 !MFI.isFixedObjectIndex(ObjectIdx: B->getIndex()))) {
140 IsAlias = false;
141 return true;
142 }
143 }
144
145 bool IsFI0 = isa<FrameIndexSDNode>(Val: BasePtr0.getBase());
146 bool IsFI1 = isa<FrameIndexSDNode>(Val: BasePtr1.getBase());
147 bool IsGV0 = isa<GlobalAddressSDNode>(Val: BasePtr0.getBase());
148 bool IsGV1 = isa<GlobalAddressSDNode>(Val: BasePtr1.getBase());
149 bool IsCV0 = isa<ConstantPoolSDNode>(Val: BasePtr0.getBase());
150 bool IsCV1 = isa<ConstantPoolSDNode>(Val: BasePtr1.getBase());
151
152 if ((IsFI0 || IsGV0 || IsCV0) && (IsFI1 || IsGV1 || IsCV1)) {
153 // We can derive NoAlias In case of mismatched base types.
154 if (IsFI0 != IsFI1 || IsGV0 != IsGV1 || IsCV0 != IsCV1) {
155 IsAlias = false;
156 return true;
157 }
158 if (IsGV0 && IsGV1) {
159 auto *GV0 = cast<GlobalAddressSDNode>(Val: BasePtr0.getBase())->getGlobal();
160 auto *GV1 = cast<GlobalAddressSDNode>(Val: BasePtr1.getBase())->getGlobal();
161 // It doesn't make sense to access one global value using another globals
162 // values address, so we can assume that there is no aliasing in case of
163 // two different globals (unless we have symbols that may indirectly point
164 // to each other).
165 // FIXME: This is perhaps a bit too defensive. We could try to follow the
166 // chain with aliasee information for GlobalAlias variables to find out if
167 // we indirect symbols may alias or not.
168 if (GV0 != GV1 && !isa<GlobalAlias>(Val: GV0) && !isa<GlobalAlias>(Val: GV1)) {
169 IsAlias = false;
170 return true;
171 }
172 }
173 }
174 return false; // Cannot determine whether the pointers alias.
175}
176
177bool BaseIndexOffset::contains(const SelectionDAG &DAG, int64_t BitSize,
178 const BaseIndexOffset &Other,
179 int64_t OtherBitSize, int64_t &BitOffset) const {
180 int64_t Offset;
181 if (!equalBaseIndex(Other, DAG, Off&: Offset))
182 return false;
183 if (Offset >= 0) {
184 // Other is after *this:
185 // [-------*this---------]
186 // [---Other--]
187 // ==Offset==>
188 BitOffset = 8 * Offset;
189 return BitOffset + OtherBitSize <= BitSize;
190 }
191 // Other starts strictly before *this, it cannot be fully contained.
192 // [-------*this---------]
193 // [--Other--]
194 return false;
195}
196
197/// Parses tree in Ptr for base, index, offset addresses.
198static BaseIndexOffset matchLSNode(const LSBaseSDNode *N,
199 const SelectionDAG &DAG) {
200 SDValue Ptr = N->getBasePtr();
201
202 // (((B + I*M) + c)) + c ...
203 SDValue Base = DAG.getTargetLoweringInfo().unwrapAddress(N: Ptr);
204 SDValue Index = SDValue();
205 int64_t Offset = 0;
206 bool IsIndexSignExt = false;
207
208 // pre-inc/pre-dec ops are components of EA.
209 if (N->getAddressingMode() == ISD::PRE_INC) {
210 if (auto *C = dyn_cast<ConstantSDNode>(Val: N->getOffset()))
211 Offset += C->getSExtValue();
212 else // If unknown, give up now.
213 return BaseIndexOffset(SDValue(), SDValue(), 0, false);
214 } else if (N->getAddressingMode() == ISD::PRE_DEC) {
215 if (auto *C = dyn_cast<ConstantSDNode>(Val: N->getOffset()))
216 Offset -= C->getSExtValue();
217 else // If unknown, give up now.
218 return BaseIndexOffset(SDValue(), SDValue(), 0, false);
219 }
220
221 // Consume constant adds & ors with appropriate masking.
222 while (true) {
223 switch (Base->getOpcode()) {
224 case ISD::OR:
225 // Only consider ORs which act as adds.
226 if (auto *C = dyn_cast<ConstantSDNode>(Val: Base->getOperand(Num: 1)))
227 if (DAG.MaskedValueIsZero(Op: Base->getOperand(Num: 0), Mask: C->getAPIntValue())) {
228 Offset += C->getSExtValue();
229 Base = DAG.getTargetLoweringInfo().unwrapAddress(N: Base->getOperand(Num: 0));
230 continue;
231 }
232 break;
233 case ISD::ADD:
234 case ISD::PTRADD:
235 if (auto *C = dyn_cast<ConstantSDNode>(Val: Base->getOperand(Num: 1))) {
236 Offset += C->getSExtValue();
237 Base = DAG.getTargetLoweringInfo().unwrapAddress(N: Base->getOperand(Num: 0));
238 continue;
239 }
240 break;
241 case ISD::LOAD:
242 case ISD::STORE: {
243 auto *LSBase = cast<LSBaseSDNode>(Val: Base.getNode());
244 unsigned int IndexResNo = (Base->getOpcode() == ISD::LOAD) ? 1 : 0;
245 if (LSBase->isIndexed() && Base.getResNo() == IndexResNo)
246 if (auto *C = dyn_cast<ConstantSDNode>(Val: LSBase->getOffset())) {
247 auto Off = C->getSExtValue();
248 if (LSBase->getAddressingMode() == ISD::PRE_DEC ||
249 LSBase->getAddressingMode() == ISD::POST_DEC)
250 Offset -= Off;
251 else
252 Offset += Off;
253 Base = DAG.getTargetLoweringInfo().unwrapAddress(N: LSBase->getBasePtr());
254 continue;
255 }
256 break;
257 }
258 }
259 // If we get here break out of the loop.
260 break;
261 }
262
263 if (Base->isAnyAdd()) {
264 // TODO: The following code appears to be needless as it just
265 // bails on some Ptrs early, reducing the cases where we
266 // find equivalence. We should be able to remove this.
267 // Inside a loop the current BASE pointer is calculated using an ADD and a
268 // MUL instruction. In this case Base is the actual BASE pointer.
269 // (i64 add (i64 %array_ptr)
270 // (i64 mul (i64 %induction_var)
271 // (i64 %element_size)))
272 if (Base->getOperand(Num: 1)->getOpcode() == ISD::MUL)
273 return BaseIndexOffset(Base, Index, Offset, IsIndexSignExt);
274
275 // Look at Base + Index + Offset cases.
276 Index = Base->getOperand(Num: 1);
277 SDValue PotentialBase = Base->getOperand(Num: 0);
278
279 // Skip signextends.
280 if (Index->getOpcode() == ISD::SIGN_EXTEND) {
281 Index = Index->getOperand(Num: 0);
282 IsIndexSignExt = true;
283 }
284
285 // Check if Index Offset pattern
286 if (!Index->isAnyAdd() || !isa<ConstantSDNode>(Val: Index->getOperand(Num: 1)))
287 return BaseIndexOffset(PotentialBase, Index, Offset, IsIndexSignExt);
288
289 Offset += cast<ConstantSDNode>(Val: Index->getOperand(Num: 1))->getSExtValue();
290 Index = Index->getOperand(Num: 0);
291 if (Index->getOpcode() == ISD::SIGN_EXTEND) {
292 Index = Index->getOperand(Num: 0);
293 IsIndexSignExt = true;
294 } else
295 IsIndexSignExt = false;
296 Base = PotentialBase;
297 }
298 return BaseIndexOffset(Base, Index, Offset, IsIndexSignExt);
299}
300
301BaseIndexOffset BaseIndexOffset::match(const SDNode *N,
302 const SelectionDAG &DAG) {
303 if (const auto *LS0 = dyn_cast<LSBaseSDNode>(Val: N))
304 return matchLSNode(N: LS0, DAG);
305 if (const auto *LN = dyn_cast<LifetimeSDNode>(Val: N)) {
306 if (LN->hasOffset())
307 return BaseIndexOffset(LN->getOperand(Num: 1), SDValue(), LN->getOffset(),
308 false);
309 return BaseIndexOffset(LN->getOperand(Num: 1), SDValue(), false);
310 }
311 return BaseIndexOffset();
312}
313
314#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
315
316LLVM_DUMP_METHOD void BaseIndexOffset::dump() const {
317 print(dbgs());
318}
319
320void BaseIndexOffset::print(raw_ostream& OS) const {
321 OS << "BaseIndexOffset base=[";
322 Base->print(OS);
323 OS << "] index=[";
324 if (Index)
325 Index->print(OS);
326 OS << "] offset=" << Offset;
327}
328
329#endif
330