1 //===-- llvm/CodeGen/SelectionDAGAddressAnalysis.cpp ------- DAG Address
2 //Analysis ---*- C++ -*-===//
3 //
4 //                     The LLVM Compiler Infrastructure
5 //
6 // This file is distributed under the University of Illinois Open Source
7 // License. See LICENSE.TXT for details.
8 //
9 //===----------------------------------------------------------------------===//
10 //
11 
12 #include "llvm/CodeGen/SelectionDAGAddressAnalysis.h"
13 #include "llvm/CodeGen/ISDOpcodes.h"
14 #include "llvm/CodeGen/MachineFrameInfo.h"
15 #include "llvm/CodeGen/SelectionDAG.h"
16 #include "llvm/CodeGen/SelectionDAGNodes.h"
17 
18 namespace llvm {
19 
20 bool BaseIndexOffset::equalBaseIndex(BaseIndexOffset &Other,
21                                      const SelectionDAG &DAG, int64_t &Off) {
22   // Initial Offset difference.
23   Off = Other.Offset - Offset;
24 
25   if ((Other.Index == Index) && (Other.IsIndexSignExt == IsIndexSignExt)) {
26     // Trivial match.
27     if (Other.Base == Base)
28       return true;
29 
30     // Match GlobalAddresses
31     if (auto *A = dyn_cast<GlobalAddressSDNode>(Base))
32       if (auto *B = dyn_cast<GlobalAddressSDNode>(Other.Base))
33         if (A->getGlobal() == B->getGlobal()) {
34           Off += B->getOffset() - A->getOffset();
35           return true;
36         }
37 
38     const MachineFrameInfo &MFI = DAG.getMachineFunction().getFrameInfo();
39 
40     // Match non-equal FrameIndexes - If both frame indices are fixed
41     // we know their relative offsets and can compare them. Otherwise
42     // we must be conservative.
43     if (auto *A = dyn_cast<FrameIndexSDNode>(Base))
44       if (auto *B = dyn_cast<FrameIndexSDNode>(Other.Base))
45         if (MFI.isFixedObjectIndex(A->getIndex()) &&
46             MFI.isFixedObjectIndex(B->getIndex())) {
47           Off += MFI.getObjectOffset(B->getIndex()) -
48                  MFI.getObjectOffset(A->getIndex());
49           return true;
50         }
51   }
52   return false;
53 }
54 
55 /// Parses tree in Ptr for base, index, offset addresses.
56 BaseIndexOffset BaseIndexOffset::match(SDValue Ptr, const SelectionDAG &DAG) {
57   // (((B + I*M) + c)) + c ...
58   SDValue Base = Ptr;
59   SDValue Index = SDValue();
60   int64_t Offset = 0;
61   bool IsIndexSignExt = false;
62 
63   // Consume constant adds & ors with appropriate masking.
64   while (Base->getOpcode() == ISD::ADD || Base->getOpcode() == ISD::OR) {
65     if (auto *C = dyn_cast<ConstantSDNode>(Base->getOperand(1))) {
66       // Only consider ORs which act as adds.
67       if (Base->getOpcode() == ISD::OR &&
68           !DAG.MaskedValueIsZero(Base->getOperand(0), C->getAPIntValue()))
69         break;
70       Offset += C->getSExtValue();
71       Base = Base->getOperand(0);
72       continue;
73     }
74     break;
75   }
76 
77   if (Base->getOpcode() == ISD::ADD) {
78     // TODO: The following code appears to be needless as it just
79     //       bails on some Ptrs early, reducing the cases where we
80     //       find equivalence. We should be able to remove this.
81     // Inside a loop the current BASE pointer is calculated using an ADD and a
82     // MUL instruction. In this case Base is the actual BASE pointer.
83     // (i64 add (i64 %array_ptr)
84     //          (i64 mul (i64 %induction_var)
85     //                   (i64 %element_size)))
86     if (Base->getOperand(1)->getOpcode() == ISD::MUL)
87       return BaseIndexOffset(Base, Index, Offset, IsIndexSignExt);
88 
89     // Look at Base + Index + Offset cases.
90     Index = Base->getOperand(1);
91     SDValue PotentialBase = Base->getOperand(0);
92 
93     // Skip signextends.
94     if (Index->getOpcode() == ISD::SIGN_EXTEND) {
95       Index = Index->getOperand(0);
96       IsIndexSignExt = true;
97     }
98 
99     // Check if Index Offset pattern
100     if (Index->getOpcode() != ISD::ADD ||
101         !isa<ConstantSDNode>(Index->getOperand(1)))
102       return BaseIndexOffset(PotentialBase, Index, Offset, IsIndexSignExt);
103 
104     Offset += cast<ConstantSDNode>(Index->getOperand(1))->getSExtValue();
105     Index = Index->getOperand(0);
106     if (Index->getOpcode() == ISD::SIGN_EXTEND) {
107       Index = Index->getOperand(0);
108       IsIndexSignExt = true;
109     } else
110       IsIndexSignExt = false;
111     Base = PotentialBase;
112   }
113   return BaseIndexOffset(Base, Index, Offset, IsIndexSignExt);
114 }
115 } // end namespace llvm
116