1 //==- llvm/CodeGen/SelectionDAGAddressAnalysis.cpp - DAG Address Analysis --==//
2 //
3 //                     The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 
10 #include "llvm/CodeGen/SelectionDAGAddressAnalysis.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/Support/Casting.h"
18 #include <cstdint>
19 
20 using namespace llvm;
21 
equalBaseIndex(const BaseIndexOffset & Other,const SelectionDAG & DAG,int64_t & Off) const22 bool 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   // Initial Offset difference.
29   Off = Other.Offset - Offset;
30 
31   if ((Other.Index == Index) && (Other.IsIndexSignExt == IsIndexSignExt)) {
32     // Trivial match.
33     if (Other.Base == Base)
34       return true;
35 
36     // Match GlobalAddresses
37     if (auto *A = dyn_cast<GlobalAddressSDNode>(Base))
38       if (auto *B = dyn_cast<GlobalAddressSDNode>(Other.Base))
39         if (A->getGlobal() == B->getGlobal()) {
40           Off += B->getOffset() - A->getOffset();
41           return true;
42         }
43 
44     // Match Constants
45     if (auto *A = dyn_cast<ConstantPoolSDNode>(Base))
46       if (auto *B = dyn_cast<ConstantPoolSDNode>(Other.Base)) {
47         bool IsMatch =
48             A->isMachineConstantPoolEntry() == B->isMachineConstantPoolEntry();
49         if (IsMatch) {
50           if (A->isMachineConstantPoolEntry())
51             IsMatch = A->getMachineCPVal() == B->getMachineCPVal();
52           else
53             IsMatch = A->getConstVal() == B->getConstVal();
54         }
55         if (IsMatch) {
56           Off += B->getOffset() - A->getOffset();
57           return true;
58         }
59       }
60 
61     const MachineFrameInfo &MFI = DAG.getMachineFunction().getFrameInfo();
62 
63     // Match non-equal FrameIndexes - If both frame indices are fixed
64     // we know their relative offsets and can compare them. Otherwise
65     // we must be conservative.
66     if (auto *A = dyn_cast<FrameIndexSDNode>(Base))
67       if (auto *B = dyn_cast<FrameIndexSDNode>(Other.Base))
68         if (MFI.isFixedObjectIndex(A->getIndex()) &&
69             MFI.isFixedObjectIndex(B->getIndex())) {
70           Off += MFI.getObjectOffset(B->getIndex()) -
71                  MFI.getObjectOffset(A->getIndex());
72           return true;
73         }
74   }
75   return false;
76 }
77 
78 /// Parses tree in Ptr for base, index, offset addresses.
match(const LSBaseSDNode * N,const SelectionDAG & DAG)79 BaseIndexOffset BaseIndexOffset::match(const LSBaseSDNode *N,
80                                        const SelectionDAG &DAG) {
81   SDValue Ptr = N->getBasePtr();
82 
83   // (((B + I*M) + c)) + c ...
84   SDValue Base = DAG.getTargetLoweringInfo().unwrapAddress(Ptr);
85   SDValue Index = SDValue();
86   int64_t Offset = 0;
87   bool IsIndexSignExt = false;
88 
89   // pre-inc/pre-dec ops are components of EA.
90   if (N->getAddressingMode() == ISD::PRE_INC) {
91     if (auto *C = dyn_cast<ConstantSDNode>(N->getOffset()))
92       Offset += C->getSExtValue();
93     else // If unknown, give up now.
94       return BaseIndexOffset(SDValue(), SDValue(), 0, false);
95   } else if (N->getAddressingMode() == ISD::PRE_DEC) {
96     if (auto *C = dyn_cast<ConstantSDNode>(N->getOffset()))
97       Offset -= C->getSExtValue();
98     else // If unknown, give up now.
99       return BaseIndexOffset(SDValue(), SDValue(), 0, false);
100   }
101 
102   // Consume constant adds & ors with appropriate masking.
103   while (true) {
104     switch (Base->getOpcode()) {
105     case ISD::OR:
106       // Only consider ORs which act as adds.
107       if (auto *C = dyn_cast<ConstantSDNode>(Base->getOperand(1)))
108         if (DAG.MaskedValueIsZero(Base->getOperand(0), C->getAPIntValue())) {
109           Offset += C->getSExtValue();
110           Base = DAG.getTargetLoweringInfo().unwrapAddress(Base->getOperand(0));
111           continue;
112         }
113       break;
114     case ISD::ADD:
115       if (auto *C = dyn_cast<ConstantSDNode>(Base->getOperand(1))) {
116         Offset += C->getSExtValue();
117         Base = DAG.getTargetLoweringInfo().unwrapAddress(Base->getOperand(0));
118         continue;
119       }
120       break;
121     case ISD::LOAD:
122     case ISD::STORE: {
123       auto *LSBase = cast<LSBaseSDNode>(Base.getNode());
124       unsigned int IndexResNo = (Base->getOpcode() == ISD::LOAD) ? 1 : 0;
125       if (LSBase->isIndexed() && Base.getResNo() == IndexResNo)
126         if (auto *C = dyn_cast<ConstantSDNode>(LSBase->getOffset())) {
127           auto Off = C->getSExtValue();
128           if (LSBase->getAddressingMode() == ISD::PRE_DEC ||
129               LSBase->getAddressingMode() == ISD::POST_DEC)
130             Offset -= Off;
131           else
132             Offset += Off;
133           Base = DAG.getTargetLoweringInfo().unwrapAddress(LSBase->getBasePtr());
134           continue;
135         }
136       break;
137     }
138     }
139     // If we get here break out of the loop.
140     break;
141   }
142 
143   if (Base->getOpcode() == ISD::ADD) {
144     // TODO: The following code appears to be needless as it just
145     //       bails on some Ptrs early, reducing the cases where we
146     //       find equivalence. We should be able to remove this.
147     // Inside a loop the current BASE pointer is calculated using an ADD and a
148     // MUL instruction. In this case Base is the actual BASE pointer.
149     // (i64 add (i64 %array_ptr)
150     //          (i64 mul (i64 %induction_var)
151     //                   (i64 %element_size)))
152     if (Base->getOperand(1)->getOpcode() == ISD::MUL)
153       return BaseIndexOffset(Base, Index, Offset, IsIndexSignExt);
154 
155     // Look at Base + Index + Offset cases.
156     Index = Base->getOperand(1);
157     SDValue PotentialBase = Base->getOperand(0);
158 
159     // Skip signextends.
160     if (Index->getOpcode() == ISD::SIGN_EXTEND) {
161       Index = Index->getOperand(0);
162       IsIndexSignExt = true;
163     }
164 
165     // Check if Index Offset pattern
166     if (Index->getOpcode() != ISD::ADD ||
167         !isa<ConstantSDNode>(Index->getOperand(1)))
168       return BaseIndexOffset(PotentialBase, Index, Offset, IsIndexSignExt);
169 
170     Offset += cast<ConstantSDNode>(Index->getOperand(1))->getSExtValue();
171     Index = Index->getOperand(0);
172     if (Index->getOpcode() == ISD::SIGN_EXTEND) {
173       Index = Index->getOperand(0);
174       IsIndexSignExt = true;
175     } else
176       IsIndexSignExt = false;
177     Base = PotentialBase;
178   }
179   return BaseIndexOffset(Base, Index, Offset, IsIndexSignExt);
180 }
181