1 //===-- AVRMCCodeEmitter.cpp - Convert AVR Code to Machine Code -----------===//
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 // This file implements the AVRMCCodeEmitter class.
10 //
11 //===----------------------------------------------------------------------===//
12 
13 #include "AVRMCCodeEmitter.h"
14 
15 #include "MCTargetDesc/AVRMCExpr.h"
16 #include "MCTargetDesc/AVRMCTargetDesc.h"
17 
18 #include "llvm/ADT/APFloat.h"
19 #include "llvm/ADT/SmallVector.h"
20 #include "llvm/MC/MCContext.h"
21 #include "llvm/MC/MCExpr.h"
22 #include "llvm/MC/MCFixup.h"
23 #include "llvm/MC/MCInst.h"
24 #include "llvm/MC/MCInstrInfo.h"
25 #include "llvm/MC/MCRegisterInfo.h"
26 #include "llvm/MC/MCSubtargetInfo.h"
27 #include "llvm/Support/Casting.h"
28 #include "llvm/Support/EndianStream.h"
29 #include "llvm/Support/raw_ostream.h"
30 
31 #define DEBUG_TYPE "mccodeemitter"
32 
33 #define GET_INSTRMAP_INFO
34 #include "AVRGenInstrInfo.inc"
35 #undef GET_INSTRMAP_INFO
36 
37 namespace llvm {
38 
39 /// Performs a post-encoding step on a `LD` or `ST` instruction.
40 ///
41 /// The encoding of the LD/ST family of instructions is inconsistent w.r.t
42 /// the pointer register and the addressing mode.
43 ///
44 /// The permutations of the format are as followed:
45 /// ld Rd, X    `1001 000d dddd 1100`
46 /// ld Rd, X+   `1001 000d dddd 1101`
47 /// ld Rd, -X   `1001 000d dddd 1110`
48 ///
49 /// ld Rd, Y    `1000 000d dddd 1000`
50 /// ld Rd, Y+   `1001 000d dddd 1001`
51 /// ld Rd, -Y   `1001 000d dddd 1010`
52 ///
53 /// ld Rd, Z    `1000 000d dddd 0000`
54 /// ld Rd, Z+   `1001 000d dddd 0001`
55 /// ld Rd, -Z   `1001 000d dddd 0010`
56 ///                 ^
57 ///                 |
58 /// Note this one inconsistent bit - it is 1 sometimes and 0 at other times.
59 /// There is no logical pattern. Looking at a truth table, the following
60 /// formula can be derived to fit the pattern:
61 //
62 /// ```
63 /// inconsistent_bit = is_predec OR is_postinc OR is_reg_x
64 /// ```
65 //
66 /// We manually set this bit in this post encoder method.
67 unsigned
68 AVRMCCodeEmitter::loadStorePostEncoder(const MCInst &MI, unsigned EncodedValue,
69                                        const MCSubtargetInfo &STI) const {
70 
71   assert(MI.getOperand(0).isReg() && MI.getOperand(1).isReg() &&
72          "the load/store operands must be registers");
73 
74   unsigned Opcode = MI.getOpcode();
75 
76   // check whether either of the registers are the X pointer register.
77   bool IsRegX = MI.getOperand(0).getReg() == AVR::R27R26 ||
78                 MI.getOperand(1).getReg() == AVR::R27R26;
79 
80   bool IsPredec = Opcode == AVR::LDRdPtrPd || Opcode == AVR::STPtrPdRr;
81   bool IsPostinc = Opcode == AVR::LDRdPtrPi || Opcode == AVR::STPtrPiRr;
82 
83   // Check if we need to set the inconsistent bit
84   if (IsRegX || IsPredec || IsPostinc) {
85     EncodedValue |= (1 << 12);
86   }
87 
88   return EncodedValue;
89 }
90 
91 template <AVR::Fixups Fixup>
92 unsigned
93 AVRMCCodeEmitter::encodeRelCondBrTarget(const MCInst &MI, unsigned OpNo,
94                                         SmallVectorImpl<MCFixup> &Fixups,
95                                         const MCSubtargetInfo &STI) const {
96   const MCOperand &MO = MI.getOperand(OpNo);
97 
98   if (MO.isExpr()) {
99     Fixups.push_back(
100         MCFixup::create(0, MO.getExpr(), MCFixupKind(Fixup), MI.getLoc()));
101     return 0;
102   }
103 
104   assert(MO.isImm());
105 
106   // Take the size of the current instruction away.
107   // With labels, this is implicitly done.
108   auto target = MO.getImm();
109   AVR::fixups::adjustBranchTarget(target);
110   return target;
111 }
112 
113 unsigned AVRMCCodeEmitter::encodeLDSTPtrReg(const MCInst &MI, unsigned OpNo,
114                                             SmallVectorImpl<MCFixup> &Fixups,
115                                             const MCSubtargetInfo &STI) const {
116   auto MO = MI.getOperand(OpNo);
117 
118   // The operand should be a pointer register.
119   assert(MO.isReg());
120 
121   switch (MO.getReg()) {
122   case AVR::R27R26:
123     return 0x03; // X: 0b11
124   case AVR::R29R28:
125     return 0x02; // Y: 0b10
126   case AVR::R31R30:
127     return 0x00; // Z: 0b00
128   default:
129     llvm_unreachable("invalid pointer register");
130   }
131 }
132 
133 /// Encodes a `memri` operand.
134 /// The operand is 7-bits.
135 /// * The lower 6 bits is the immediate
136 /// * The upper bit is the pointer register bit (Z=0,Y=1)
137 unsigned AVRMCCodeEmitter::encodeMemri(const MCInst &MI, unsigned OpNo,
138                                        SmallVectorImpl<MCFixup> &Fixups,
139                                        const MCSubtargetInfo &STI) const {
140   auto RegOp = MI.getOperand(OpNo);
141   auto OffsetOp = MI.getOperand(OpNo + 1);
142 
143   assert(RegOp.isReg() && "Expected register operand");
144 
145   uint8_t RegBit = 0;
146 
147   switch (RegOp.getReg()) {
148   default:
149     llvm_unreachable("Expected either Y or Z register");
150   case AVR::R31R30:
151     RegBit = 0;
152     break; // Z register
153   case AVR::R29R28:
154     RegBit = 1;
155     break; // Y register
156   }
157 
158   int8_t OffsetBits;
159 
160   if (OffsetOp.isImm()) {
161     OffsetBits = OffsetOp.getImm();
162   } else if (OffsetOp.isExpr()) {
163     OffsetBits = 0;
164     Fixups.push_back(MCFixup::create(0, OffsetOp.getExpr(),
165                                      MCFixupKind(AVR::fixup_6), MI.getLoc()));
166   } else {
167     llvm_unreachable("invalid value for offset");
168   }
169 
170   return (RegBit << 6) | OffsetBits;
171 }
172 
173 unsigned AVRMCCodeEmitter::encodeComplement(const MCInst &MI, unsigned OpNo,
174                                             SmallVectorImpl<MCFixup> &Fixups,
175                                             const MCSubtargetInfo &STI) const {
176   // The operand should be an immediate.
177   assert(MI.getOperand(OpNo).isImm());
178 
179   auto Imm = MI.getOperand(OpNo).getImm();
180   return (~0) - Imm;
181 }
182 
183 template <AVR::Fixups Fixup, unsigned Offset>
184 unsigned AVRMCCodeEmitter::encodeImm(const MCInst &MI, unsigned OpNo,
185                                      SmallVectorImpl<MCFixup> &Fixups,
186                                      const MCSubtargetInfo &STI) const {
187   auto MO = MI.getOperand(OpNo);
188 
189   if (MO.isExpr()) {
190     if (isa<AVRMCExpr>(MO.getExpr())) {
191       // If the expression is already an AVRMCExpr (i.e. a lo8(symbol),
192       // we shouldn't perform any more fixups. Without this check, we would
193       // instead create a fixup to the symbol named 'lo8(symbol)' which
194       // is not correct.
195       return getExprOpValue(MO.getExpr(), Fixups, STI);
196     }
197 
198     MCFixupKind FixupKind = static_cast<MCFixupKind>(Fixup);
199     Fixups.push_back(
200         MCFixup::create(Offset, MO.getExpr(), FixupKind, MI.getLoc()));
201 
202     return 0;
203   }
204 
205   assert(MO.isImm());
206   return MO.getImm();
207 }
208 
209 unsigned AVRMCCodeEmitter::encodeCallTarget(const MCInst &MI, unsigned OpNo,
210                                             SmallVectorImpl<MCFixup> &Fixups,
211                                             const MCSubtargetInfo &STI) const {
212   auto MO = MI.getOperand(OpNo);
213 
214   if (MO.isExpr()) {
215     MCFixupKind FixupKind = static_cast<MCFixupKind>(AVR::fixup_call);
216     Fixups.push_back(MCFixup::create(0, MO.getExpr(), FixupKind, MI.getLoc()));
217     return 0;
218   }
219 
220   assert(MO.isImm());
221 
222   auto Target = MO.getImm();
223   AVR::fixups::adjustBranchTarget(Target);
224   return Target;
225 }
226 
227 unsigned AVRMCCodeEmitter::getExprOpValue(const MCExpr *Expr,
228                                           SmallVectorImpl<MCFixup> &Fixups,
229                                           const MCSubtargetInfo &STI) const {
230 
231   MCExpr::ExprKind Kind = Expr->getKind();
232 
233   if (Kind == MCExpr::Binary) {
234     Expr = static_cast<const MCBinaryExpr *>(Expr)->getLHS();
235     Kind = Expr->getKind();
236   }
237 
238   if (Kind == MCExpr::Target) {
239     AVRMCExpr const *AVRExpr = cast<AVRMCExpr>(Expr);
240     int64_t Result;
241     if (AVRExpr->evaluateAsConstant(Result)) {
242       return Result;
243     }
244 
245     MCFixupKind FixupKind = static_cast<MCFixupKind>(AVRExpr->getFixupKind());
246     Fixups.push_back(MCFixup::create(0, AVRExpr, FixupKind));
247     return 0;
248   }
249 
250   assert(Kind == MCExpr::SymbolRef);
251   return 0;
252 }
253 
254 unsigned AVRMCCodeEmitter::getMachineOpValue(const MCInst &MI,
255                                              const MCOperand &MO,
256                                              SmallVectorImpl<MCFixup> &Fixups,
257                                              const MCSubtargetInfo &STI) const {
258   if (MO.isReg())
259     return Ctx.getRegisterInfo()->getEncodingValue(MO.getReg());
260   if (MO.isImm())
261     return static_cast<unsigned>(MO.getImm());
262 
263   if (MO.isDFPImm())
264     return static_cast<unsigned>(bit_cast<double>(MO.getDFPImm()));
265 
266   // MO must be an Expr.
267   assert(MO.isExpr());
268 
269   return getExprOpValue(MO.getExpr(), Fixups, STI);
270 }
271 
272 void AVRMCCodeEmitter::emitInstruction(uint64_t Val, unsigned Size,
273                                        const MCSubtargetInfo &STI,
274                                        raw_ostream &OS) const {
275   size_t WordCount = Size / 2;
276 
277   for (int64_t i = WordCount - 1; i >= 0; --i) {
278     uint16_t Word = (Val >> (i * 16)) & 0xFFFF;
279     support::endian::write(OS, Word, support::endianness::little);
280   }
281 }
282 
283 void AVRMCCodeEmitter::encodeInstruction(const MCInst &MI, raw_ostream &OS,
284                                          SmallVectorImpl<MCFixup> &Fixups,
285                                          const MCSubtargetInfo &STI) const {
286   const MCInstrDesc &Desc = MCII.get(MI.getOpcode());
287 
288   // Get byte count of instruction
289   unsigned Size = Desc.getSize();
290 
291   assert(Size > 0 && "Instruction size cannot be zero");
292 
293   uint64_t BinaryOpCode = getBinaryCodeForInstr(MI, Fixups, STI);
294   emitInstruction(BinaryOpCode, Size, STI, OS);
295 }
296 
297 MCCodeEmitter *createAVRMCCodeEmitter(const MCInstrInfo &MCII,
298                                       MCContext &Ctx) {
299   return new AVRMCCodeEmitter(MCII, Ctx);
300 }
301 
302 #include "AVRGenMCCodeEmitter.inc"
303 
304 } // end of namespace llvm
305