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 
22 bool BaseIndexOffset::equalBaseIndex(BaseIndexOffset &Other,
23                                      const SelectionDAG &DAG, int64_t &Off) {
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 non-equal FrameIndexes - If both frame indices are fixed
63     // we know their relative offsets and can compare them. Otherwise
64     // we must be conservative.
65     if (auto *A = dyn_cast<FrameIndexSDNode>(Base))
66       if (auto *B = dyn_cast<FrameIndexSDNode>(Other.Base))
67         if (MFI.isFixedObjectIndex(A->getIndex()) &&
68             MFI.isFixedObjectIndex(B->getIndex())) {
69           Off += MFI.getObjectOffset(B->getIndex()) -
70                  MFI.getObjectOffset(A->getIndex());
71           return true;
72         }
73   }
74   return false;
75 }
76 
77 /// Parses tree in Ptr for base, index, offset addresses.
78 BaseIndexOffset BaseIndexOffset::match(LSBaseSDNode *N,
79                                        const SelectionDAG &DAG) {
80   SDValue Ptr = N->getBasePtr();
81 
82   // (((B + I*M) + c)) + c ...
83   SDValue Base = DAG.getTargetLoweringInfo().unwrapAddress(Ptr);
84   SDValue Index = SDValue();
85   int64_t Offset = 0;
86   bool IsIndexSignExt = false;
87 
88   // pre-inc/pre-dec ops are components of EA.
89   if (N->getAddressingMode() == ISD::PRE_INC) {
90     if (auto *C = dyn_cast<ConstantSDNode>(N->getOffset()))
91       Offset += C->getSExtValue();
92     else // If unknown, give up now.
93       return BaseIndexOffset(SDValue(), SDValue(), 0, false);
94   } else if (N->getAddressingMode() == ISD::PRE_DEC) {
95     if (auto *C = dyn_cast<ConstantSDNode>(N->getOffset()))
96       Offset -= C->getSExtValue();
97     else // If unknown, give up now.
98       return BaseIndexOffset(SDValue(), SDValue(), 0, false);
99   }
100 
101   // Consume constant adds & ors with appropriate masking.
102   while (true) {
103     switch (Base->getOpcode()) {
104     case ISD::OR:
105       // Only consider ORs which act as adds.
106       if (auto *C = dyn_cast<ConstantSDNode>(Base->getOperand(1)))
107         if (DAG.MaskedValueIsZero(Base->getOperand(0), C->getAPIntValue())) {
108           Offset += C->getSExtValue();
109           Base = Base->getOperand(0);
110           continue;
111         }
112       break;
113     case ISD::ADD:
114       if (auto *C = dyn_cast<ConstantSDNode>(Base->getOperand(1))) {
115         Offset += C->getSExtValue();
116         Base = Base->getOperand(0);
117         continue;
118       }
119       break;
120     case ISD::LOAD:
121     case ISD::STORE: {
122       auto *LSBase = cast<LSBaseSDNode>(Base.getNode());
123       unsigned int IndexResNo = (Base->getOpcode() == ISD::LOAD) ? 1 : 0;
124       if (LSBase->isIndexed() && Base.getResNo() == IndexResNo)
125         if (auto *C = dyn_cast<ConstantSDNode>(LSBase->getOffset())) {
126           auto Off = C->getSExtValue();
127           if (LSBase->getAddressingMode() == ISD::PRE_DEC ||
128               LSBase->getAddressingMode() == ISD::POST_DEC)
129             Offset -= Off;
130           else
131             Offset += Off;
132           Base = LSBase->getBasePtr();
133           continue;
134         }
135       break;
136     }
137     }
138     // If we get here break out of the loop.
139     break;
140   }
141 
142   if (Base->getOpcode() == ISD::ADD) {
143     // TODO: The following code appears to be needless as it just
144     //       bails on some Ptrs early, reducing the cases where we
145     //       find equivalence. We should be able to remove this.
146     // Inside a loop the current BASE pointer is calculated using an ADD and a
147     // MUL instruction. In this case Base is the actual BASE pointer.
148     // (i64 add (i64 %array_ptr)
149     //          (i64 mul (i64 %induction_var)
150     //                   (i64 %element_size)))
151     if (Base->getOperand(1)->getOpcode() == ISD::MUL)
152       return BaseIndexOffset(Base, Index, Offset, IsIndexSignExt);
153 
154     // Look at Base + Index + Offset cases.
155     Index = Base->getOperand(1);
156     SDValue PotentialBase = Base->getOperand(0);
157 
158     // Skip signextends.
159     if (Index->getOpcode() == ISD::SIGN_EXTEND) {
160       Index = Index->getOperand(0);
161       IsIndexSignExt = true;
162     }
163 
164     // Check if Index Offset pattern
165     if (Index->getOpcode() != ISD::ADD ||
166         !isa<ConstantSDNode>(Index->getOperand(1)))
167       return BaseIndexOffset(PotentialBase, Index, Offset, IsIndexSignExt);
168 
169     Offset += cast<ConstantSDNode>(Index->getOperand(1))->getSExtValue();
170     Index = Index->getOperand(0);
171     if (Index->getOpcode() == ISD::SIGN_EXTEND) {
172       Index = Index->getOperand(0);
173       IsIndexSignExt = true;
174     } else
175       IsIndexSignExt = false;
176     Base = PotentialBase;
177   }
178   return BaseIndexOffset(Base, Index, Offset, IsIndexSignExt);
179 }
180