1 //===-- SIMCCodeEmitter.cpp - SI Code Emitter -----------------------------===//
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 /// \file
10 /// The SI code emitter produces machine code that can be executed
11 /// directly on the GPU device.
12 //
13 //===----------------------------------------------------------------------===//
14 
15 #include "MCTargetDesc/AMDGPUFixupKinds.h"
16 #include "MCTargetDesc/AMDGPUMCCodeEmitter.h"
17 #include "MCTargetDesc/AMDGPUMCTargetDesc.h"
18 #include "SIDefines.h"
19 #include "Utils/AMDGPUBaseInfo.h"
20 #include "llvm/ADT/APInt.h"
21 #include "llvm/MC/MCCodeEmitter.h"
22 #include "llvm/MC/MCContext.h"
23 #include "llvm/MC/MCExpr.h"
24 #include "llvm/MC/MCInstrInfo.h"
25 #include "llvm/MC/MCRegisterInfo.h"
26 #include "llvm/MC/MCSubtargetInfo.h"
27 #include "llvm/MC/SubtargetFeature.h"
28 #include "llvm/Support/Casting.h"
29 
30 using namespace llvm;
31 
32 namespace {
33 
34 class SIMCCodeEmitter : public  AMDGPUMCCodeEmitter {
35   const MCRegisterInfo &MRI;
36 
37   /// Encode an fp or int literal
38   uint32_t getLitEncoding(const MCOperand &MO, const MCOperandInfo &OpInfo,
39                           const MCSubtargetInfo &STI) const;
40 
41 public:
42   SIMCCodeEmitter(const MCInstrInfo &mcii, MCContext &ctx)
43       : AMDGPUMCCodeEmitter(mcii), MRI(*ctx.getRegisterInfo()) {}
44   SIMCCodeEmitter(const SIMCCodeEmitter &) = delete;
45   SIMCCodeEmitter &operator=(const SIMCCodeEmitter &) = delete;
46 
47   /// Encode the instruction and write it to the OS.
48   void encodeInstruction(const MCInst &MI, raw_ostream &OS,
49                          SmallVectorImpl<MCFixup> &Fixups,
50                          const MCSubtargetInfo &STI) const override;
51 
52   /// \returns the encoding for an MCOperand.
53   void getMachineOpValue(const MCInst &MI, const MCOperand &MO, APInt &Op,
54                          SmallVectorImpl<MCFixup> &Fixups,
55                          const MCSubtargetInfo &STI) const override;
56 
57   /// Use a fixup to encode the simm16 field for SOPP branch
58   ///        instructions.
59   void getSOPPBrEncoding(const MCInst &MI, unsigned OpNo, APInt &Op,
60                          SmallVectorImpl<MCFixup> &Fixups,
61                          const MCSubtargetInfo &STI) const override;
62 
63   void getSMEMOffsetEncoding(const MCInst &MI, unsigned OpNo, APInt &Op,
64                              SmallVectorImpl<MCFixup> &Fixups,
65                              const MCSubtargetInfo &STI) const override;
66 
67   void getSDWASrcEncoding(const MCInst &MI, unsigned OpNo, APInt &Op,
68                           SmallVectorImpl<MCFixup> &Fixups,
69                           const MCSubtargetInfo &STI) const override;
70 
71   void getSDWAVopcDstEncoding(const MCInst &MI, unsigned OpNo, APInt &Op,
72                               SmallVectorImpl<MCFixup> &Fixups,
73                               const MCSubtargetInfo &STI) const override;
74 
75   void getAVOperandEncoding(const MCInst &MI, unsigned OpNo, APInt &Op,
76                             SmallVectorImpl<MCFixup> &Fixups,
77                             const MCSubtargetInfo &STI) const override;
78 
79 private:
80   uint64_t getImplicitOpSelHiEncoding(int Opcode) const;
81   void getMachineOpValueCommon(const MCInst &MI, const MCOperand &MO,
82                                unsigned OpNo, APInt &Op,
83                                SmallVectorImpl<MCFixup> &Fixups,
84                                const MCSubtargetInfo &STI) const;
85 };
86 
87 } // end anonymous namespace
88 
89 MCCodeEmitter *llvm::createSIMCCodeEmitter(const MCInstrInfo &MCII,
90                                            MCContext &Ctx) {
91   return new SIMCCodeEmitter(MCII, Ctx);
92 }
93 
94 // Returns the encoding value to use if the given integer is an integer inline
95 // immediate value, or 0 if it is not.
96 template <typename IntTy>
97 static uint32_t getIntInlineImmEncoding(IntTy Imm) {
98   if (Imm >= 0 && Imm <= 64)
99     return 128 + Imm;
100 
101   if (Imm >= -16 && Imm <= -1)
102     return 192 + std::abs(Imm);
103 
104   return 0;
105 }
106 
107 static uint32_t getLit16IntEncoding(uint16_t Val, const MCSubtargetInfo &STI) {
108   uint16_t IntImm = getIntInlineImmEncoding(static_cast<int16_t>(Val));
109   return IntImm == 0 ? 255 : IntImm;
110 }
111 
112 static uint32_t getLit16Encoding(uint16_t Val, const MCSubtargetInfo &STI) {
113   uint16_t IntImm = getIntInlineImmEncoding(static_cast<int16_t>(Val));
114   if (IntImm != 0)
115     return IntImm;
116 
117   if (Val == 0x3800) // 0.5
118     return 240;
119 
120   if (Val == 0xB800) // -0.5
121     return 241;
122 
123   if (Val == 0x3C00) // 1.0
124     return 242;
125 
126   if (Val == 0xBC00) // -1.0
127     return 243;
128 
129   if (Val == 0x4000) // 2.0
130     return 244;
131 
132   if (Val == 0xC000) // -2.0
133     return 245;
134 
135   if (Val == 0x4400) // 4.0
136     return 246;
137 
138   if (Val == 0xC400) // -4.0
139     return 247;
140 
141   if (Val == 0x3118 && // 1.0 / (2.0 * pi)
142       STI.getFeatureBits()[AMDGPU::FeatureInv2PiInlineImm])
143     return 248;
144 
145   return 255;
146 }
147 
148 static uint32_t getLit32Encoding(uint32_t Val, const MCSubtargetInfo &STI) {
149   uint32_t IntImm = getIntInlineImmEncoding(static_cast<int32_t>(Val));
150   if (IntImm != 0)
151     return IntImm;
152 
153   if (Val == FloatToBits(0.5f))
154     return 240;
155 
156   if (Val == FloatToBits(-0.5f))
157     return 241;
158 
159   if (Val == FloatToBits(1.0f))
160     return 242;
161 
162   if (Val == FloatToBits(-1.0f))
163     return 243;
164 
165   if (Val == FloatToBits(2.0f))
166     return 244;
167 
168   if (Val == FloatToBits(-2.0f))
169     return 245;
170 
171   if (Val == FloatToBits(4.0f))
172     return 246;
173 
174   if (Val == FloatToBits(-4.0f))
175     return 247;
176 
177   if (Val == 0x3e22f983 && // 1.0 / (2.0 * pi)
178       STI.getFeatureBits()[AMDGPU::FeatureInv2PiInlineImm])
179     return 248;
180 
181   return 255;
182 }
183 
184 static uint32_t getLit64Encoding(uint64_t Val, const MCSubtargetInfo &STI) {
185   uint32_t IntImm = getIntInlineImmEncoding(static_cast<int64_t>(Val));
186   if (IntImm != 0)
187     return IntImm;
188 
189   if (Val == DoubleToBits(0.5))
190     return 240;
191 
192   if (Val == DoubleToBits(-0.5))
193     return 241;
194 
195   if (Val == DoubleToBits(1.0))
196     return 242;
197 
198   if (Val == DoubleToBits(-1.0))
199     return 243;
200 
201   if (Val == DoubleToBits(2.0))
202     return 244;
203 
204   if (Val == DoubleToBits(-2.0))
205     return 245;
206 
207   if (Val == DoubleToBits(4.0))
208     return 246;
209 
210   if (Val == DoubleToBits(-4.0))
211     return 247;
212 
213   if (Val == 0x3fc45f306dc9c882 && // 1.0 / (2.0 * pi)
214       STI.getFeatureBits()[AMDGPU::FeatureInv2PiInlineImm])
215     return 248;
216 
217   return 255;
218 }
219 
220 uint32_t SIMCCodeEmitter::getLitEncoding(const MCOperand &MO,
221                                          const MCOperandInfo &OpInfo,
222                                          const MCSubtargetInfo &STI) const {
223   int64_t Imm;
224   if (MO.isExpr()) {
225     const auto *C = dyn_cast<MCConstantExpr>(MO.getExpr());
226     if (!C)
227       return 255;
228 
229     Imm = C->getValue();
230   } else {
231 
232     assert(!MO.isDFPImm());
233 
234     if (!MO.isImm())
235       return ~0;
236 
237     Imm = MO.getImm();
238   }
239 
240   switch (OpInfo.OperandType) {
241   case AMDGPU::OPERAND_REG_IMM_INT32:
242   case AMDGPU::OPERAND_REG_IMM_FP32:
243   case AMDGPU::OPERAND_REG_IMM_FP32_DEFERRED:
244   case AMDGPU::OPERAND_REG_INLINE_C_INT32:
245   case AMDGPU::OPERAND_REG_INLINE_C_FP32:
246   case AMDGPU::OPERAND_REG_INLINE_AC_INT32:
247   case AMDGPU::OPERAND_REG_INLINE_AC_FP32:
248   case AMDGPU::OPERAND_REG_IMM_V2INT32:
249   case AMDGPU::OPERAND_REG_IMM_V2FP32:
250   case AMDGPU::OPERAND_REG_INLINE_C_V2INT32:
251   case AMDGPU::OPERAND_REG_INLINE_C_V2FP32:
252     return getLit32Encoding(static_cast<uint32_t>(Imm), STI);
253 
254   case AMDGPU::OPERAND_REG_IMM_INT64:
255   case AMDGPU::OPERAND_REG_IMM_FP64:
256   case AMDGPU::OPERAND_REG_INLINE_C_INT64:
257   case AMDGPU::OPERAND_REG_INLINE_C_FP64:
258   case AMDGPU::OPERAND_REG_INLINE_AC_FP64:
259     return getLit64Encoding(static_cast<uint64_t>(Imm), STI);
260 
261   case AMDGPU::OPERAND_REG_IMM_INT16:
262   case AMDGPU::OPERAND_REG_INLINE_C_INT16:
263   case AMDGPU::OPERAND_REG_INLINE_AC_INT16:
264     return getLit16IntEncoding(static_cast<uint16_t>(Imm), STI);
265   case AMDGPU::OPERAND_REG_IMM_FP16:
266   case AMDGPU::OPERAND_REG_IMM_FP16_DEFERRED:
267   case AMDGPU::OPERAND_REG_INLINE_C_FP16:
268   case AMDGPU::OPERAND_REG_INLINE_AC_FP16:
269     // FIXME Is this correct? What do inline immediates do on SI for f16 src
270     // which does not have f16 support?
271     return getLit16Encoding(static_cast<uint16_t>(Imm), STI);
272   case AMDGPU::OPERAND_REG_IMM_V2INT16:
273   case AMDGPU::OPERAND_REG_IMM_V2FP16: {
274     if (!isUInt<16>(Imm) && STI.getFeatureBits()[AMDGPU::FeatureVOP3Literal])
275       return getLit32Encoding(static_cast<uint32_t>(Imm), STI);
276     if (OpInfo.OperandType == AMDGPU::OPERAND_REG_IMM_V2FP16)
277       return getLit16Encoding(static_cast<uint16_t>(Imm), STI);
278     LLVM_FALLTHROUGH;
279   }
280   case AMDGPU::OPERAND_REG_INLINE_C_V2INT16:
281   case AMDGPU::OPERAND_REG_INLINE_AC_V2INT16:
282     return getLit16IntEncoding(static_cast<uint16_t>(Imm), STI);
283   case AMDGPU::OPERAND_REG_INLINE_C_V2FP16:
284   case AMDGPU::OPERAND_REG_INLINE_AC_V2FP16: {
285     uint16_t Lo16 = static_cast<uint16_t>(Imm);
286     uint32_t Encoding = getLit16Encoding(Lo16, STI);
287     return Encoding;
288   }
289   case AMDGPU::OPERAND_KIMM32:
290   case AMDGPU::OPERAND_KIMM16:
291     return MO.getImm();
292   default:
293     llvm_unreachable("invalid operand size");
294   }
295 }
296 
297 uint64_t SIMCCodeEmitter::getImplicitOpSelHiEncoding(int Opcode) const {
298   using namespace AMDGPU::VOP3PEncoding;
299   using namespace AMDGPU::OpName;
300 
301   if (AMDGPU::getNamedOperandIdx(Opcode, op_sel_hi) != -1) {
302     if (AMDGPU::getNamedOperandIdx(Opcode, src2) != -1)
303       return 0;
304     if (AMDGPU::getNamedOperandIdx(Opcode, src1) != -1)
305       return OP_SEL_HI_2;
306     if (AMDGPU::getNamedOperandIdx(Opcode, src0) != -1)
307       return OP_SEL_HI_1 | OP_SEL_HI_2;
308   }
309   return OP_SEL_HI_0 | OP_SEL_HI_1 | OP_SEL_HI_2;
310 }
311 
312 void SIMCCodeEmitter::encodeInstruction(const MCInst &MI, raw_ostream &OS,
313                                         SmallVectorImpl<MCFixup> &Fixups,
314                                         const MCSubtargetInfo &STI) const {
315   int Opcode = MI.getOpcode();
316   APInt Encoding, Scratch;
317   getBinaryCodeForInstr(MI, Fixups, Encoding, Scratch,  STI);
318   const MCInstrDesc &Desc = MCII.get(MI.getOpcode());
319   unsigned bytes = Desc.getSize();
320 
321   // Set unused op_sel_hi bits to 1 for VOP3P and MAI instructions.
322   // Note that accvgpr_read/write are MAI, have src0, but do not use op_sel.
323   if ((Desc.TSFlags & SIInstrFlags::VOP3P) ||
324       Opcode == AMDGPU::V_ACCVGPR_READ_B32_vi ||
325       Opcode == AMDGPU::V_ACCVGPR_WRITE_B32_vi) {
326     Encoding |= getImplicitOpSelHiEncoding(Opcode);
327   }
328 
329   for (unsigned i = 0; i < bytes; i++) {
330     OS.write((uint8_t)Encoding.extractBitsAsZExtValue(8, 8 * i));
331   }
332 
333   // NSA encoding.
334   if (AMDGPU::isGFX10Plus(STI) && Desc.TSFlags & SIInstrFlags::MIMG) {
335     int vaddr0 = AMDGPU::getNamedOperandIdx(MI.getOpcode(),
336                                             AMDGPU::OpName::vaddr0);
337     int srsrc = AMDGPU::getNamedOperandIdx(MI.getOpcode(),
338                                            AMDGPU::OpName::srsrc);
339     assert(vaddr0 >= 0 && srsrc > vaddr0);
340     unsigned NumExtraAddrs = srsrc - vaddr0 - 1;
341     unsigned NumPadding = (-NumExtraAddrs) & 3;
342 
343     for (unsigned i = 0; i < NumExtraAddrs; ++i) {
344       getMachineOpValue(MI, MI.getOperand(vaddr0 + 1 + i), Encoding, Fixups,
345                         STI);
346       OS.write((uint8_t)Encoding.getLimitedValue());
347     }
348     for (unsigned i = 0; i < NumPadding; ++i)
349       OS.write(0);
350   }
351 
352   if ((bytes > 8 && STI.getFeatureBits()[AMDGPU::FeatureVOP3Literal]) ||
353       (bytes > 4 && !STI.getFeatureBits()[AMDGPU::FeatureVOP3Literal]))
354     return;
355 
356   // Do not print literals from SISrc Operands for insts with mandatory literals
357   int ImmLitIdx =
358       AMDGPU::getNamedOperandIdx(MI.getOpcode(), AMDGPU::OpName::imm);
359   if (ImmLitIdx != -1)
360     return;
361 
362   // Check for additional literals
363   for (unsigned i = 0, e = Desc.getNumOperands(); i < e; ++i) {
364 
365     // Check if this operand should be encoded as [SV]Src
366     if (!AMDGPU::isSISrcOperand(Desc, i))
367       continue;
368 
369     // Is this operand a literal immediate?
370     const MCOperand &Op = MI.getOperand(i);
371     if (getLitEncoding(Op, Desc.OpInfo[i], STI) != 255)
372       continue;
373 
374     // Yes! Encode it
375     int64_t Imm = 0;
376 
377     if (Op.isImm())
378       Imm = Op.getImm();
379     else if (Op.isExpr()) {
380       if (const auto *C = dyn_cast<MCConstantExpr>(Op.getExpr()))
381         Imm = C->getValue();
382 
383     } else if (!Op.isExpr()) // Exprs will be replaced with a fixup value.
384       llvm_unreachable("Must be immediate or expr");
385 
386     for (unsigned j = 0; j < 4; j++) {
387       OS.write((uint8_t) ((Imm >> (8 * j)) & 0xff));
388     }
389 
390     // Only one literal value allowed
391     break;
392   }
393 }
394 
395 void SIMCCodeEmitter::getSOPPBrEncoding(const MCInst &MI, unsigned OpNo,
396                                         APInt &Op,
397                                         SmallVectorImpl<MCFixup> &Fixups,
398                                         const MCSubtargetInfo &STI) const {
399   const MCOperand &MO = MI.getOperand(OpNo);
400 
401   if (MO.isExpr()) {
402     const MCExpr *Expr = MO.getExpr();
403     MCFixupKind Kind = (MCFixupKind)AMDGPU::fixup_si_sopp_br;
404     Fixups.push_back(MCFixup::create(0, Expr, Kind, MI.getLoc()));
405     Op = APInt::getNullValue(96);
406   } else {
407     getMachineOpValue(MI, MO, Op, Fixups, STI);
408   }
409 }
410 
411 void SIMCCodeEmitter::getSMEMOffsetEncoding(const MCInst &MI, unsigned OpNo,
412                                             APInt &Op,
413                                             SmallVectorImpl<MCFixup> &Fixups,
414                                             const MCSubtargetInfo &STI) const {
415   auto Offset = MI.getOperand(OpNo).getImm();
416   // VI only supports 20-bit unsigned offsets.
417   assert(!AMDGPU::isVI(STI) || isUInt<20>(Offset));
418   Op = Offset;
419 }
420 
421 void SIMCCodeEmitter::getSDWASrcEncoding(const MCInst &MI, unsigned OpNo,
422                                          APInt &Op,
423                                          SmallVectorImpl<MCFixup> &Fixups,
424                                          const MCSubtargetInfo &STI) const {
425   using namespace AMDGPU::SDWA;
426 
427   uint64_t RegEnc = 0;
428 
429   const MCOperand &MO = MI.getOperand(OpNo);
430 
431   if (MO.isReg()) {
432     unsigned Reg = MO.getReg();
433     RegEnc |= MRI.getEncodingValue(Reg);
434     RegEnc &= SDWA9EncValues::SRC_VGPR_MASK;
435     if (AMDGPU::isSGPR(AMDGPU::mc2PseudoReg(Reg), &MRI)) {
436       RegEnc |= SDWA9EncValues::SRC_SGPR_MASK;
437     }
438     Op = RegEnc;
439     return;
440   } else {
441     const MCInstrDesc &Desc = MCII.get(MI.getOpcode());
442     uint32_t Enc = getLitEncoding(MO, Desc.OpInfo[OpNo], STI);
443     if (Enc != ~0U && Enc != 255) {
444       Op = Enc | SDWA9EncValues::SRC_SGPR_MASK;
445       return;
446     }
447   }
448 
449   llvm_unreachable("Unsupported operand kind");
450 }
451 
452 void SIMCCodeEmitter::getSDWAVopcDstEncoding(const MCInst &MI, unsigned OpNo,
453                                              APInt &Op,
454                                              SmallVectorImpl<MCFixup> &Fixups,
455                                              const MCSubtargetInfo &STI) const {
456   using namespace AMDGPU::SDWA;
457 
458   uint64_t RegEnc = 0;
459 
460   const MCOperand &MO = MI.getOperand(OpNo);
461 
462   unsigned Reg = MO.getReg();
463   if (Reg != AMDGPU::VCC && Reg != AMDGPU::VCC_LO) {
464     RegEnc |= MRI.getEncodingValue(Reg);
465     RegEnc &= SDWA9EncValues::VOPC_DST_SGPR_MASK;
466     RegEnc |= SDWA9EncValues::VOPC_DST_VCC_MASK;
467   }
468   Op = RegEnc;
469 }
470 
471 void SIMCCodeEmitter::getAVOperandEncoding(const MCInst &MI, unsigned OpNo,
472                                            APInt &Op,
473                                            SmallVectorImpl<MCFixup> &Fixups,
474                                            const MCSubtargetInfo &STI) const {
475   unsigned Reg = MI.getOperand(OpNo).getReg();
476   uint64_t Enc = MRI.getEncodingValue(Reg);
477 
478   // VGPR and AGPR have the same encoding, but SrcA and SrcB operands of mfma
479   // instructions use acc[0:1] modifier bits to distinguish. These bits are
480   // encoded as a virtual 9th bit of the register for these operands.
481   if (MRI.getRegClass(AMDGPU::AGPR_32RegClassID).contains(Reg) ||
482       MRI.getRegClass(AMDGPU::AReg_64RegClassID).contains(Reg) ||
483       MRI.getRegClass(AMDGPU::AReg_96RegClassID).contains(Reg) ||
484       MRI.getRegClass(AMDGPU::AReg_128RegClassID).contains(Reg) ||
485       MRI.getRegClass(AMDGPU::AReg_160RegClassID).contains(Reg) ||
486       MRI.getRegClass(AMDGPU::AReg_192RegClassID).contains(Reg) ||
487       MRI.getRegClass(AMDGPU::AReg_224RegClassID).contains(Reg) ||
488       MRI.getRegClass(AMDGPU::AReg_256RegClassID).contains(Reg) ||
489       MRI.getRegClass(AMDGPU::AReg_512RegClassID).contains(Reg) ||
490       MRI.getRegClass(AMDGPU::AGPR_LO16RegClassID).contains(Reg))
491     Enc |= 512;
492 
493   Op = Enc;
494 }
495 
496 static bool needsPCRel(const MCExpr *Expr) {
497   switch (Expr->getKind()) {
498   case MCExpr::SymbolRef: {
499     auto *SE = cast<MCSymbolRefExpr>(Expr);
500     MCSymbolRefExpr::VariantKind Kind = SE->getKind();
501     return Kind != MCSymbolRefExpr::VK_AMDGPU_ABS32_LO &&
502            Kind != MCSymbolRefExpr::VK_AMDGPU_ABS32_HI;
503   }
504   case MCExpr::Binary: {
505     auto *BE = cast<MCBinaryExpr>(Expr);
506     if (BE->getOpcode() == MCBinaryExpr::Sub)
507       return false;
508     return needsPCRel(BE->getLHS()) || needsPCRel(BE->getRHS());
509   }
510   case MCExpr::Unary:
511     return needsPCRel(cast<MCUnaryExpr>(Expr)->getSubExpr());
512   case MCExpr::Target:
513   case MCExpr::Constant:
514     return false;
515   }
516   llvm_unreachable("invalid kind");
517 }
518 
519 void SIMCCodeEmitter::getMachineOpValue(const MCInst &MI,
520                                         const MCOperand &MO, APInt &Op,
521                                         SmallVectorImpl<MCFixup> &Fixups,
522                                         const MCSubtargetInfo &STI) const {
523   if (MO.isReg()){
524     Op = MRI.getEncodingValue(MO.getReg());
525     return;
526   }
527   unsigned OpNo = &MO - MI.begin();
528   getMachineOpValueCommon(MI, MO, OpNo, Op, Fixups, STI);
529 }
530 
531 void SIMCCodeEmitter::getMachineOpValueCommon(
532     const MCInst &MI, const MCOperand &MO, unsigned OpNo, APInt &Op,
533     SmallVectorImpl<MCFixup> &Fixups, const MCSubtargetInfo &STI) const {
534 
535   if (MO.isExpr() && MO.getExpr()->getKind() != MCExpr::Constant) {
536     // FIXME: If this is expression is PCRel or not should not depend on what
537     // the expression looks like. Given that this is just a general expression,
538     // it should probably be FK_Data_4 and whatever is producing
539     //
540     //    s_add_u32 s2, s2, (extern_const_addrspace+16
541     //
542     // And expecting a PCRel should instead produce
543     //
544     // .Ltmp1:
545     //   s_add_u32 s2, s2, (extern_const_addrspace+16)-.Ltmp1
546     MCFixupKind Kind;
547     if (needsPCRel(MO.getExpr()))
548       Kind = FK_PCRel_4;
549     else
550       Kind = FK_Data_4;
551 
552     const MCInstrDesc &Desc = MCII.get(MI.getOpcode());
553     uint32_t Offset = Desc.getSize();
554     assert(Offset == 4 || Offset == 8);
555 
556     Fixups.push_back(MCFixup::create(Offset, MO.getExpr(), Kind, MI.getLoc()));
557   }
558 
559   const MCInstrDesc &Desc = MCII.get(MI.getOpcode());
560   if (AMDGPU::isSISrcOperand(Desc, OpNo)) {
561     uint32_t Enc = getLitEncoding(MO, Desc.OpInfo[OpNo], STI);
562     if (Enc != ~0U) {
563       Op = Enc;
564       return;
565     }
566   } else if (MO.isImm()) {
567     Op = MO.getImm();
568     return;
569   }
570 
571   llvm_unreachable("Encoding of this operand type is not supported yet.");
572 }
573 
574 #include "AMDGPUGenMCCodeEmitter.inc"
575