1 //===- MipsAnalyzeImmediate.cpp - Analyze Immediates ----------------------===//
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 "MipsAnalyzeImmediate.h"
10 #include "Mips.h"
11 #include "llvm/Support/MathExtras.h"
12 #include <cassert>
13 #include <cstdint>
14 #include <iterator>
15 
16 using namespace llvm;
17 
18 MipsAnalyzeImmediate::Inst::Inst(unsigned O, unsigned I) : Opc(O), ImmOpnd(I) {}
19 
20 // Add I to the instruction sequences.
21 void MipsAnalyzeImmediate::AddInstr(InstSeqLs &SeqLs, const Inst &I) {
22   // Add an instruction seqeunce consisting of just I.
23   if (SeqLs.empty()) {
24     SeqLs.push_back(InstSeq(1, I));
25     return;
26   }
27 
28   for (auto &S : SeqLs)
29     S.push_back(I);
30 }
31 
32 void MipsAnalyzeImmediate::GetInstSeqLsADDiu(uint64_t Imm, unsigned RemSize,
33                                              InstSeqLs &SeqLs) {
34   GetInstSeqLs((Imm + 0x8000ULL) & 0xffffffffffff0000ULL, RemSize, SeqLs);
35   AddInstr(SeqLs, Inst(ADDiu, Imm & 0xffffULL));
36 }
37 
38 void MipsAnalyzeImmediate::GetInstSeqLsORi(uint64_t Imm, unsigned RemSize,
39                                            InstSeqLs &SeqLs) {
40   GetInstSeqLs(Imm & 0xffffffffffff0000ULL, RemSize, SeqLs);
41   AddInstr(SeqLs, Inst(ORi, Imm & 0xffffULL));
42 }
43 
44 void MipsAnalyzeImmediate::GetInstSeqLsSLL(uint64_t Imm, unsigned RemSize,
45                                            InstSeqLs &SeqLs) {
46   unsigned Shamt = llvm::countr_zero(Imm);
47   GetInstSeqLs(Imm >> Shamt, RemSize - Shamt, SeqLs);
48   AddInstr(SeqLs, Inst(SLL, Shamt));
49 }
50 
51 void MipsAnalyzeImmediate::GetInstSeqLs(uint64_t Imm, unsigned RemSize,
52                                         InstSeqLs &SeqLs) {
53   uint64_t MaskedImm = Imm & (0xffffffffffffffffULL >> (64 - Size));
54 
55   // Do nothing if Imm is 0.
56   if (!MaskedImm)
57     return;
58 
59   // A single ADDiu will do if RemSize <= 16.
60   if (RemSize <= 16) {
61     AddInstr(SeqLs, Inst(ADDiu, MaskedImm));
62     return;
63   }
64 
65   // Shift if the lower 16-bit is cleared.
66   if (!(Imm & 0xffff)) {
67     GetInstSeqLsSLL(Imm, RemSize, SeqLs);
68     return;
69   }
70 
71   GetInstSeqLsADDiu(Imm, RemSize, SeqLs);
72 
73   // If bit 15 is cleared, it doesn't make a difference whether the last
74   // instruction is an ADDiu or ORi. In that case, do not call GetInstSeqLsORi.
75   if (Imm & 0x8000) {
76     InstSeqLs SeqLsORi;
77     GetInstSeqLsORi(Imm, RemSize, SeqLsORi);
78     SeqLs.append(std::make_move_iterator(SeqLsORi.begin()),
79                  std::make_move_iterator(SeqLsORi.end()));
80   }
81 }
82 
83 // Replace a ADDiu & SLL pair with a LUi.
84 // e.g. the following two instructions
85 //  ADDiu 0x0111
86 //  SLL 18
87 // are replaced with
88 //  LUi 0x444
89 void MipsAnalyzeImmediate::ReplaceADDiuSLLWithLUi(InstSeq &Seq) {
90   // Check if the first two instructions are ADDiu and SLL and the shift amount
91   // is at least 16.
92   if ((Seq.size() < 2) || (Seq[0].Opc != ADDiu) ||
93       (Seq[1].Opc != SLL) || (Seq[1].ImmOpnd < 16))
94     return;
95 
96   // Sign-extend and shift operand of ADDiu and see if it still fits in 16-bit.
97   int64_t Imm = SignExtend64<16>(Seq[0].ImmOpnd);
98   int64_t ShiftedImm = (uint64_t)Imm << (Seq[1].ImmOpnd - 16);
99 
100   if (!isInt<16>(ShiftedImm))
101     return;
102 
103   // Replace the first instruction and erase the second.
104   Seq[0].Opc = LUi;
105   Seq[0].ImmOpnd = (unsigned)(ShiftedImm & 0xffff);
106   Seq.erase(Seq.begin() + 1);
107 }
108 
109 void MipsAnalyzeImmediate::GetShortestSeq(InstSeqLs &SeqLs, InstSeq &Insts) {
110   InstSeqLs::iterator ShortestSeq = SeqLs.end();
111   // The length of an instruction sequence is at most 7.
112   unsigned ShortestLength = 8;
113 
114   for (InstSeqLs::iterator S = SeqLs.begin(); S != SeqLs.end(); ++S) {
115     ReplaceADDiuSLLWithLUi(*S);
116     assert(S->size() <= 7);
117 
118     if (S->size() < ShortestLength) {
119       ShortestSeq = S;
120       ShortestLength = S->size();
121     }
122   }
123 
124   Insts.clear();
125   Insts.append(ShortestSeq->begin(), ShortestSeq->end());
126 }
127 
128 const MipsAnalyzeImmediate::InstSeq
129 &MipsAnalyzeImmediate::Analyze(uint64_t Imm, unsigned Size,
130                                bool LastInstrIsADDiu) {
131   this->Size = Size;
132 
133   if (Size == 32) {
134     ADDiu = Mips::ADDiu;
135     ORi = Mips::ORi;
136     SLL = Mips::SLL;
137     LUi = Mips::LUi;
138   } else {
139     ADDiu = Mips::DADDiu;
140     ORi = Mips::ORi64;
141     SLL = Mips::DSLL;
142     LUi = Mips::LUi64;
143   }
144 
145   InstSeqLs SeqLs;
146 
147   // Get the list of instruction sequences.
148   if (LastInstrIsADDiu | !Imm)
149     GetInstSeqLsADDiu(Imm, Size, SeqLs);
150   else
151     GetInstSeqLs(Imm, Size, SeqLs);
152 
153   // Set Insts to the shortest instruction sequence.
154   GetShortestSeq(SeqLs, Insts);
155 
156   return Insts;
157 }
158