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   // Initial Offset difference.
25   Off = Other.Offset - Offset;
26 
27   if ((Other.Index == Index) && (Other.IsIndexSignExt == IsIndexSignExt)) {
28     // Trivial match.
29     if (Other.Base == Base)
30       return true;
31 
32     // Match GlobalAddresses
33     if (auto *A = dyn_cast<GlobalAddressSDNode>(Base))
34       if (auto *B = dyn_cast<GlobalAddressSDNode>(Other.Base))
35         if (A->getGlobal() == B->getGlobal()) {
36           Off += B->getOffset() - A->getOffset();
37           return true;
38         }
39 
40     const MachineFrameInfo &MFI = DAG.getMachineFunction().getFrameInfo();
41 
42     // Match non-equal FrameIndexes - If both frame indices are fixed
43     // we know their relative offsets and can compare them. Otherwise
44     // we must be conservative.
45     if (auto *A = dyn_cast<FrameIndexSDNode>(Base))
46       if (auto *B = dyn_cast<FrameIndexSDNode>(Other.Base))
47         if (MFI.isFixedObjectIndex(A->getIndex()) &&
48             MFI.isFixedObjectIndex(B->getIndex())) {
49           Off += MFI.getObjectOffset(B->getIndex()) -
50                  MFI.getObjectOffset(A->getIndex());
51           return true;
52         }
53   }
54   return false;
55 }
56 
57 /// Parses tree in Ptr for base, index, offset addresses.
58 BaseIndexOffset BaseIndexOffset::match(SDValue Ptr, const SelectionDAG &DAG) {
59   // (((B + I*M) + c)) + c ...
60   SDValue Base = DAG.getTargetLoweringInfo().unwrapAddress(Ptr);
61   SDValue Index = SDValue();
62   int64_t Offset = 0;
63   bool IsIndexSignExt = false;
64 
65   // Consume constant adds & ors with appropriate masking.
66   while (Base->getOpcode() == ISD::ADD || Base->getOpcode() == ISD::OR) {
67     if (auto *C = dyn_cast<ConstantSDNode>(Base->getOperand(1))) {
68       // Only consider ORs which act as adds.
69       if (Base->getOpcode() == ISD::OR &&
70           !DAG.MaskedValueIsZero(Base->getOperand(0), C->getAPIntValue()))
71         break;
72       Offset += C->getSExtValue();
73       Base = Base->getOperand(0);
74       continue;
75     }
76     break;
77   }
78 
79   if (Base->getOpcode() == ISD::ADD) {
80     // TODO: The following code appears to be needless as it just
81     //       bails on some Ptrs early, reducing the cases where we
82     //       find equivalence. We should be able to remove this.
83     // Inside a loop the current BASE pointer is calculated using an ADD and a
84     // MUL instruction. In this case Base is the actual BASE pointer.
85     // (i64 add (i64 %array_ptr)
86     //          (i64 mul (i64 %induction_var)
87     //                   (i64 %element_size)))
88     if (Base->getOperand(1)->getOpcode() == ISD::MUL)
89       return BaseIndexOffset(Base, Index, Offset, IsIndexSignExt);
90 
91     // Look at Base + Index + Offset cases.
92     Index = Base->getOperand(1);
93     SDValue PotentialBase = Base->getOperand(0);
94 
95     // Skip signextends.
96     if (Index->getOpcode() == ISD::SIGN_EXTEND) {
97       Index = Index->getOperand(0);
98       IsIndexSignExt = true;
99     }
100 
101     // Check if Index Offset pattern
102     if (Index->getOpcode() != ISD::ADD ||
103         !isa<ConstantSDNode>(Index->getOperand(1)))
104       return BaseIndexOffset(PotentialBase, Index, Offset, IsIndexSignExt);
105 
106     Offset += cast<ConstantSDNode>(Index->getOperand(1))->getSExtValue();
107     Index = Index->getOperand(0);
108     if (Index->getOpcode() == ISD::SIGN_EXTEND) {
109       Index = Index->getOperand(0);
110       IsIndexSignExt = true;
111     } else
112       IsIndexSignExt = false;
113     Base = PotentialBase;
114   }
115   return BaseIndexOffset(Base, Index, Offset, IsIndexSignExt);
116 }
117