1 //===-- RISCVMCCodeEmitter.cpp - Convert RISCV 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 RISCVMCCodeEmitter class.
10 //
11 //===----------------------------------------------------------------------===//
12 
13 #include "MCTargetDesc/RISCVFixupKinds.h"
14 #include "MCTargetDesc/RISCVMCExpr.h"
15 #include "MCTargetDesc/RISCVMCTargetDesc.h"
16 #include "Utils/RISCVBaseInfo.h"
17 #include "llvm/ADT/Statistic.h"
18 #include "llvm/MC/MCAsmInfo.h"
19 #include "llvm/MC/MCCodeEmitter.h"
20 #include "llvm/MC/MCContext.h"
21 #include "llvm/MC/MCExpr.h"
22 #include "llvm/MC/MCInst.h"
23 #include "llvm/MC/MCInstBuilder.h"
24 #include "llvm/MC/MCInstrInfo.h"
25 #include "llvm/MC/MCRegisterInfo.h"
26 #include "llvm/MC/MCSymbol.h"
27 #include "llvm/Support/Casting.h"
28 #include "llvm/Support/EndianStream.h"
29 #include "llvm/Support/raw_ostream.h"
30 
31 using namespace llvm;
32 
33 #define DEBUG_TYPE "mccodeemitter"
34 
35 STATISTIC(MCNumEmitted, "Number of MC instructions emitted");
36 STATISTIC(MCNumFixups, "Number of MC fixups created");
37 
38 namespace {
39 class RISCVMCCodeEmitter : public MCCodeEmitter {
40   RISCVMCCodeEmitter(const RISCVMCCodeEmitter &) = delete;
41   void operator=(const RISCVMCCodeEmitter &) = delete;
42   MCContext &Ctx;
43   MCInstrInfo const &MCII;
44 
45 public:
46   RISCVMCCodeEmitter(MCContext &ctx, MCInstrInfo const &MCII)
47       : Ctx(ctx), MCII(MCII) {}
48 
49   ~RISCVMCCodeEmitter() override {}
50 
51   void encodeInstruction(const MCInst &MI, raw_ostream &OS,
52                          SmallVectorImpl<MCFixup> &Fixups,
53                          const MCSubtargetInfo &STI) const override;
54 
55   void expandFunctionCall(const MCInst &MI, raw_ostream &OS,
56                           SmallVectorImpl<MCFixup> &Fixups,
57                           const MCSubtargetInfo &STI) const;
58 
59   /// TableGen'erated function for getting the binary encoding for an
60   /// instruction.
61   uint64_t getBinaryCodeForInstr(const MCInst &MI,
62                                  SmallVectorImpl<MCFixup> &Fixups,
63                                  const MCSubtargetInfo &STI) const;
64 
65   /// Return binary encoding of operand. If the machine operand requires
66   /// relocation, record the relocation and return zero.
67   unsigned getMachineOpValue(const MCInst &MI, const MCOperand &MO,
68                              SmallVectorImpl<MCFixup> &Fixups,
69                              const MCSubtargetInfo &STI) const;
70 
71   unsigned getImmOpValueAsr1(const MCInst &MI, unsigned OpNo,
72                              SmallVectorImpl<MCFixup> &Fixups,
73                              const MCSubtargetInfo &STI) const;
74 
75   unsigned getImmOpValue(const MCInst &MI, unsigned OpNo,
76                          SmallVectorImpl<MCFixup> &Fixups,
77                          const MCSubtargetInfo &STI) const;
78 };
79 } // end anonymous namespace
80 
81 MCCodeEmitter *llvm::createRISCVMCCodeEmitter(const MCInstrInfo &MCII,
82                                               const MCRegisterInfo &MRI,
83                                               MCContext &Ctx) {
84   return new RISCVMCCodeEmitter(Ctx, MCII);
85 }
86 
87 // Expand PseudoCALL and PseudoTAIL to AUIPC and JALR with relocation types.
88 // We expand PseudoCALL and PseudoTAIL while encoding, meaning AUIPC and JALR
89 // won't go through RISCV MC to MC compressed instruction transformation. This
90 // is acceptable because AUIPC has no 16-bit form and C_JALR have no immediate
91 // operand field.  We let linker relaxation deal with it. When linker
92 // relaxation enabled, AUIPC and JALR have chance relax to JAL. If C extension
93 // is enabled, JAL has chance relax to C_JAL.
94 void RISCVMCCodeEmitter::expandFunctionCall(const MCInst &MI, raw_ostream &OS,
95                                             SmallVectorImpl<MCFixup> &Fixups,
96                                             const MCSubtargetInfo &STI) const {
97   MCInst TmpInst;
98   MCOperand Func = MI.getOperand(0);
99   unsigned Ra = (MI.getOpcode() == RISCV::PseudoTAIL) ? RISCV::X6 : RISCV::X1;
100   uint32_t Binary;
101 
102   assert(Func.isExpr() && "Expected expression");
103 
104   const MCExpr *CallExpr = Func.getExpr();
105 
106   // Emit AUIPC Ra, Func with R_RISCV_CALL relocation type.
107   TmpInst = MCInstBuilder(RISCV::AUIPC)
108                 .addReg(Ra)
109                 .addOperand(MCOperand::createExpr(CallExpr));
110   Binary = getBinaryCodeForInstr(TmpInst, Fixups, STI);
111   support::endian::write(OS, Binary, support::little);
112 
113   if (MI.getOpcode() == RISCV::PseudoTAIL)
114     // Emit JALR X0, X6, 0
115     TmpInst = MCInstBuilder(RISCV::JALR).addReg(RISCV::X0).addReg(Ra).addImm(0);
116   else
117     // Emit JALR X1, X1, 0
118     TmpInst = MCInstBuilder(RISCV::JALR).addReg(Ra).addReg(Ra).addImm(0);
119   Binary = getBinaryCodeForInstr(TmpInst, Fixups, STI);
120   support::endian::write(OS, Binary, support::little);
121 }
122 
123 void RISCVMCCodeEmitter::encodeInstruction(const MCInst &MI, raw_ostream &OS,
124                                            SmallVectorImpl<MCFixup> &Fixups,
125                                            const MCSubtargetInfo &STI) const {
126   const MCInstrDesc &Desc = MCII.get(MI.getOpcode());
127   // Get byte count of instruction.
128   unsigned Size = Desc.getSize();
129 
130   if (MI.getOpcode() == RISCV::PseudoCALL ||
131       MI.getOpcode() == RISCV::PseudoTAIL) {
132     expandFunctionCall(MI, OS, Fixups, STI);
133     MCNumEmitted += 2;
134     return;
135   }
136 
137   switch (Size) {
138   default:
139     llvm_unreachable("Unhandled encodeInstruction length!");
140   case 2: {
141     uint16_t Bits = getBinaryCodeForInstr(MI, Fixups, STI);
142     support::endian::write<uint16_t>(OS, Bits, support::little);
143     break;
144   }
145   case 4: {
146     uint32_t Bits = getBinaryCodeForInstr(MI, Fixups, STI);
147     support::endian::write(OS, Bits, support::little);
148     break;
149   }
150   }
151 
152   ++MCNumEmitted; // Keep track of the # of mi's emitted.
153 }
154 
155 unsigned
156 RISCVMCCodeEmitter::getMachineOpValue(const MCInst &MI, const MCOperand &MO,
157                                       SmallVectorImpl<MCFixup> &Fixups,
158                                       const MCSubtargetInfo &STI) const {
159 
160   if (MO.isReg())
161     return Ctx.getRegisterInfo()->getEncodingValue(MO.getReg());
162 
163   if (MO.isImm())
164     return static_cast<unsigned>(MO.getImm());
165 
166   llvm_unreachable("Unhandled expression!");
167   return 0;
168 }
169 
170 unsigned
171 RISCVMCCodeEmitter::getImmOpValueAsr1(const MCInst &MI, unsigned OpNo,
172                                       SmallVectorImpl<MCFixup> &Fixups,
173                                       const MCSubtargetInfo &STI) const {
174   const MCOperand &MO = MI.getOperand(OpNo);
175 
176   if (MO.isImm()) {
177     unsigned Res = MO.getImm();
178     assert((Res & 1) == 0 && "LSB is non-zero");
179     return Res >> 1;
180   }
181 
182   return getImmOpValue(MI, OpNo, Fixups, STI);
183 }
184 
185 unsigned RISCVMCCodeEmitter::getImmOpValue(const MCInst &MI, unsigned OpNo,
186                                            SmallVectorImpl<MCFixup> &Fixups,
187                                            const MCSubtargetInfo &STI) const {
188   bool EnableRelax = STI.getFeatureBits()[RISCV::FeatureRelax];
189   const MCOperand &MO = MI.getOperand(OpNo);
190 
191   MCInstrDesc const &Desc = MCII.get(MI.getOpcode());
192   unsigned MIFrm = Desc.TSFlags & RISCVII::InstFormatMask;
193 
194   // If the destination is an immediate, there is nothing to do.
195   if (MO.isImm())
196     return MO.getImm();
197 
198   assert(MO.isExpr() &&
199          "getImmOpValue expects only expressions or immediates");
200   const MCExpr *Expr = MO.getExpr();
201   MCExpr::ExprKind Kind = Expr->getKind();
202   RISCV::Fixups FixupKind = RISCV::fixup_riscv_invalid;
203   bool RelaxCandidate = false;
204   if (Kind == MCExpr::Target) {
205     const RISCVMCExpr *RVExpr = cast<RISCVMCExpr>(Expr);
206 
207     switch (RVExpr->getKind()) {
208     case RISCVMCExpr::VK_RISCV_None:
209     case RISCVMCExpr::VK_RISCV_Invalid:
210       llvm_unreachable("Unhandled fixup kind!");
211     case RISCVMCExpr::VK_RISCV_LO:
212       if (MIFrm == RISCVII::InstFormatI)
213         FixupKind = RISCV::fixup_riscv_lo12_i;
214       else if (MIFrm == RISCVII::InstFormatS)
215         FixupKind = RISCV::fixup_riscv_lo12_s;
216       else
217         llvm_unreachable("VK_RISCV_LO used with unexpected instruction format");
218       RelaxCandidate = true;
219       break;
220     case RISCVMCExpr::VK_RISCV_HI:
221       FixupKind = RISCV::fixup_riscv_hi20;
222       RelaxCandidate = true;
223       break;
224     case RISCVMCExpr::VK_RISCV_PCREL_LO:
225       if (MIFrm == RISCVII::InstFormatI)
226         FixupKind = RISCV::fixup_riscv_pcrel_lo12_i;
227       else if (MIFrm == RISCVII::InstFormatS)
228         FixupKind = RISCV::fixup_riscv_pcrel_lo12_s;
229       else
230         llvm_unreachable(
231             "VK_RISCV_PCREL_LO used with unexpected instruction format");
232       RelaxCandidate = true;
233       break;
234     case RISCVMCExpr::VK_RISCV_PCREL_HI:
235       FixupKind = RISCV::fixup_riscv_pcrel_hi20;
236       RelaxCandidate = true;
237       break;
238     case RISCVMCExpr::VK_RISCV_GOT_HI:
239       FixupKind = RISCV::fixup_riscv_got_hi20;
240       break;
241     case RISCVMCExpr::VK_RISCV_CALL:
242       FixupKind = RISCV::fixup_riscv_call;
243       RelaxCandidate = true;
244       break;
245     case RISCVMCExpr::VK_RISCV_CALL_PLT:
246       FixupKind = RISCV::fixup_riscv_call_plt;
247       RelaxCandidate = true;
248       break;
249     }
250   } else if (Kind == MCExpr::SymbolRef &&
251              cast<MCSymbolRefExpr>(Expr)->getKind() == MCSymbolRefExpr::VK_None) {
252     if (Desc.getOpcode() == RISCV::JAL) {
253       FixupKind = RISCV::fixup_riscv_jal;
254     } else if (MIFrm == RISCVII::InstFormatB) {
255       FixupKind = RISCV::fixup_riscv_branch;
256     } else if (MIFrm == RISCVII::InstFormatCJ) {
257       FixupKind = RISCV::fixup_riscv_rvc_jump;
258     } else if (MIFrm == RISCVII::InstFormatCB) {
259       FixupKind = RISCV::fixup_riscv_rvc_branch;
260     }
261   }
262 
263   assert(FixupKind != RISCV::fixup_riscv_invalid && "Unhandled expression!");
264 
265   Fixups.push_back(
266       MCFixup::create(0, Expr, MCFixupKind(FixupKind), MI.getLoc()));
267   ++MCNumFixups;
268 
269   // Ensure an R_RISCV_RELAX relocation will be emitted if linker relaxation is
270   // enabled and the current fixup will result in a relocation that may be
271   // relaxed.
272   if (EnableRelax && RelaxCandidate) {
273     const MCConstantExpr *Dummy = MCConstantExpr::create(0, Ctx);
274     Fixups.push_back(
275     MCFixup::create(0, Dummy, MCFixupKind(RISCV::fixup_riscv_relax),
276                     MI.getLoc()));
277     ++MCNumFixups;
278   }
279 
280   return 0;
281 }
282 
283 #include "RISCVGenMCCodeEmitter.inc"
284