1 //===-- X86/X86CodeEmitter.cpp - Convert X86 code to machine code ---------===//
3 // The LLVM Compiler Infrastructure
5 // This file was developed by the LLVM research group and is distributed under
6 // the University of Illinois Open Source License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file contains the pass that transforms the X86 machine instructions into
11 // actual executable machine code.
13 //===----------------------------------------------------------------------===//
15 #define DEBUG_TYPE "jit"
16 #include "X86TargetMachine.h"
18 #include "llvm/PassManager.h"
19 #include "llvm/CodeGen/MachineCodeEmitter.h"
20 #include "llvm/CodeGen/MachineFunctionPass.h"
21 #include "llvm/CodeGen/MachineInstr.h"
22 #include "llvm/CodeGen/Passes.h"
23 #include "llvm/Function.h"
24 #include "Support/Debug.h"
25 #include "Support/Statistic.h"
26 #include "Config/alloca.h"
31 NumEmitted("x86-emitter", "Number of machine instructions emitted");
34 MachineCodeEmitter &MCE;
36 // LazyCodeGenMap - Keep track of call sites for functions that are to be
38 std::map<unsigned, Function*> LazyCodeGenMap;
40 // LazyResolverMap - Keep track of the lazy resolver created for a
41 // particular function so that we can reuse them if necessary.
42 std::map<Function*, unsigned> LazyResolverMap;
44 JITResolver(MachineCodeEmitter &mce) : MCE(mce) {}
45 unsigned getLazyResolver(Function *F);
46 unsigned addFunctionReference(unsigned Address, Function *F);
49 unsigned emitStubForFunction(Function *F);
50 static void CompilationCallback();
51 unsigned resolveFunctionReference(unsigned RetAddr);
54 static JITResolver &getResolver(MachineCodeEmitter &MCE) {
55 static JITResolver *TheJITResolver = 0;
56 if (TheJITResolver == 0)
57 TheJITResolver = new JITResolver(MCE);
58 return *TheJITResolver;
63 void *X86JITInfo::getJITStubForFunction(Function *F, MachineCodeEmitter &MCE) {
64 return (void*)((unsigned long)getResolver(MCE).getLazyResolver(F));
67 void X86JITInfo::replaceMachineCodeForFunction (void *Old, void *New) {
68 char *OldByte = (char *) Old;
69 *OldByte++ = 0xE9; // Emit JMP opcode.
70 int32_t *OldWord = (int32_t *) OldByte;
71 int32_t NewAddr = (intptr_t) New;
72 int32_t OldAddr = (intptr_t) OldWord;
73 *OldWord = NewAddr - OldAddr - 4; // Emit PC-relative addr of New code.
76 /// addFunctionReference - This method is called when we need to emit the
77 /// address of a function that has not yet been emitted, so we don't know the
78 /// address. Instead, we emit a call to the CompilationCallback method, and
79 /// keep track of where we are.
81 unsigned JITResolver::addFunctionReference(unsigned Address, Function *F) {
82 LazyCodeGenMap[Address] = F;
83 return (intptr_t)&JITResolver::CompilationCallback;
86 unsigned JITResolver::resolveFunctionReference(unsigned RetAddr) {
87 std::map<unsigned, Function*>::iterator I = LazyCodeGenMap.find(RetAddr);
88 assert(I != LazyCodeGenMap.end() && "Not in map!");
89 Function *F = I->second;
90 LazyCodeGenMap.erase(I);
91 return MCE.forceCompilationOf(F);
94 unsigned JITResolver::getLazyResolver(Function *F) {
95 std::map<Function*, unsigned>::iterator I = LazyResolverMap.lower_bound(F);
96 if (I != LazyResolverMap.end() && I->first == F) return I->second;
98 //std::cerr << "Getting lazy resolver for : " << ((Value*)F)->getName() << "\n";
100 unsigned Stub = emitStubForFunction(F);
101 LazyResolverMap.insert(I, std::make_pair(F, Stub));
105 void JITResolver::CompilationCallback() {
106 unsigned *StackPtr = (unsigned*)__builtin_frame_address(0);
107 unsigned RetAddr = (unsigned)(intptr_t)__builtin_return_address(0);
108 assert(StackPtr[1] == RetAddr &&
109 "Could not find return address on the stack!");
111 // It's a stub if there is an interrupt marker after the call...
112 bool isStub = ((unsigned char*)(intptr_t)RetAddr)[0] == 0xCD;
114 // FIXME FIXME FIXME FIXME: __builtin_frame_address doesn't work if frame
115 // pointer elimination has been performed. Having a variable sized alloca
116 // disables frame pointer elimination currently, even if it's dead. This is a
119 // FIXME FIXME FIXME FIXME
121 // The call instruction should have pushed the return value onto the stack...
122 RetAddr -= 4; // Backtrack to the reference itself...
125 DEBUG(std::cerr << "In callback! Addr=0x" << std::hex << RetAddr
126 << " ESP=0x" << (unsigned)StackPtr << std::dec
127 << ": Resolving call to function: "
128 << TheVM->getFunctionReferencedName((void*)RetAddr) << "\n");
131 // Sanity check to make sure this really is a call instruction...
132 assert(((unsigned char*)(intptr_t)RetAddr)[-1] == 0xE8 &&"Not a call instr!");
134 JITResolver &JR = getResolver(*(MachineCodeEmitter*)0);
135 unsigned NewVal = JR.resolveFunctionReference(RetAddr);
137 // Rewrite the call target... so that we don't fault every time we execute
139 *(unsigned*)(intptr_t)RetAddr = NewVal-RetAddr-4;
142 // If this is a stub, rewrite the call into an unconditional branch
143 // instruction so that two return addresses are not pushed onto the stack
144 // when the requested function finally gets called. This also makes the
145 // 0xCD byte (interrupt) dead, so the marker doesn't effect anything.
146 ((unsigned char*)(intptr_t)RetAddr)[-1] = 0xE9;
149 // Change the return address to reexecute the call instruction...
153 /// emitStubForFunction - This method is used by the JIT when it needs to emit
154 /// the address of a function for a function whose code has not yet been
155 /// generated. In order to do this, it generates a stub which jumps to the lazy
156 /// function compiler, which will eventually get fixed to call the function
159 unsigned JITResolver::emitStubForFunction(Function *F) {
160 MCE.startFunctionStub(*F, 6);
161 MCE.emitByte(0xE8); // Call with 32 bit pc-rel destination...
163 unsigned Address = addFunctionReference(MCE.getCurrentPCValue(), F);
164 MCE.emitWord(Address-MCE.getCurrentPCValue()-4);
166 MCE.emitByte(0xCD); // Interrupt - Just a marker identifying the stub!
167 return (intptr_t)MCE.finishFunctionStub(*F);
173 class Emitter : public MachineFunctionPass {
174 const X86InstrInfo *II;
175 MachineCodeEmitter &MCE;
176 std::map<const BasicBlock*, unsigned> BasicBlockAddrs;
177 std::vector<std::pair<const BasicBlock*, unsigned> > BBRefs;
179 Emitter(MachineCodeEmitter &mce) : II(0), MCE(mce) {}
181 bool runOnMachineFunction(MachineFunction &MF);
183 virtual const char *getPassName() const {
184 return "X86 Machine Code Emitter";
188 void emitBasicBlock(MachineBasicBlock &MBB);
189 void emitInstruction(MachineInstr &MI);
191 void emitPCRelativeBlockAddress(BasicBlock *BB);
192 void emitMaybePCRelativeValue(unsigned Address, bool isPCRelative);
193 void emitGlobalAddressForCall(GlobalValue *GV);
194 void emitGlobalAddressForPtr(GlobalValue *GV);
196 void emitRegModRMByte(unsigned ModRMReg, unsigned RegOpcodeField);
197 void emitSIBByte(unsigned SS, unsigned Index, unsigned Base);
198 void emitConstant(unsigned Val, unsigned Size);
200 void emitMemModRMByte(const MachineInstr &MI,
201 unsigned Op, unsigned RegOpcodeField);
206 /// addPassesToEmitMachineCode - Add passes to the specified pass manager to get
207 /// machine code emitted. This uses a MachineCodeEmitter object to handle
208 /// actually outputting the machine code and resolving things like the address
209 /// of functions. This method should returns true if machine code emission is
212 bool X86TargetMachine::addPassesToEmitMachineCode(FunctionPassManager &PM,
213 MachineCodeEmitter &MCE) {
214 PM.add(new Emitter(MCE));
218 bool Emitter::runOnMachineFunction(MachineFunction &MF) {
219 II = &((X86TargetMachine&)MF.getTarget()).getInstrInfo();
221 MCE.startFunction(MF);
222 MCE.emitConstantPool(MF.getConstantPool());
223 for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I)
225 MCE.finishFunction(MF);
227 // Resolve all forward branches now...
228 for (unsigned i = 0, e = BBRefs.size(); i != e; ++i) {
229 unsigned Location = BasicBlockAddrs[BBRefs[i].first];
230 unsigned Ref = BBRefs[i].second;
231 *(unsigned*)(intptr_t)Ref = Location-Ref-4;
234 BasicBlockAddrs.clear();
238 void Emitter::emitBasicBlock(MachineBasicBlock &MBB) {
239 if (uint64_t Addr = MCE.getCurrentPCValue())
240 BasicBlockAddrs[MBB.getBasicBlock()] = Addr;
242 for (MachineBasicBlock::iterator I = MBB.begin(), E = MBB.end(); I != E; ++I)
247 /// emitPCRelativeBlockAddress - This method emits the PC relative address of
248 /// the specified basic block, or if the basic block hasn't been emitted yet
249 /// (because this is a forward branch), it keeps track of the information
250 /// necessary to resolve this address later (and emits a dummy value).
252 void Emitter::emitPCRelativeBlockAddress(BasicBlock *BB) {
253 // FIXME: Emit backward branches directly
254 BBRefs.push_back(std::make_pair(BB, MCE.getCurrentPCValue()));
255 MCE.emitWord(0); // Emit a dummy value
258 /// emitMaybePCRelativeValue - Emit a 32-bit address which may be PC relative.
260 void Emitter::emitMaybePCRelativeValue(unsigned Address, bool isPCRelative) {
262 MCE.emitWord(Address-MCE.getCurrentPCValue()-4);
264 MCE.emitWord(Address);
267 /// emitGlobalAddressForCall - Emit the specified address to the code stream
268 /// assuming this is part of a function call, which is PC relative.
270 void Emitter::emitGlobalAddressForCall(GlobalValue *GV) {
271 // Get the address from the backend...
272 unsigned Address = MCE.getGlobalValueAddress(GV);
275 // FIXME: this is JIT specific!
276 Address = getResolver(MCE).addFunctionReference(MCE.getCurrentPCValue(),
279 emitMaybePCRelativeValue(Address, true);
282 /// emitGlobalAddress - Emit the specified address to the code stream assuming
283 /// this is part of a "take the address of a global" instruction, which is not
286 void Emitter::emitGlobalAddressForPtr(GlobalValue *GV) {
287 // Get the address from the backend...
288 unsigned Address = MCE.getGlobalValueAddress(GV);
290 // If the machine code emitter doesn't know what the address IS yet, we have
291 // to take special measures.
294 // FIXME: this is JIT specific!
295 Address = getResolver(MCE).getLazyResolver((Function*)GV);
298 emitMaybePCRelativeValue(Address, false);
303 /// N86 namespace - Native X86 Register numbers... used by X86 backend.
307 EAX = 0, ECX = 1, EDX = 2, EBX = 3, ESP = 4, EBP = 5, ESI = 6, EDI = 7
312 // getX86RegNum - This function maps LLVM register identifiers to their X86
313 // specific numbering, which is used in various places encoding instructions.
315 static unsigned getX86RegNum(unsigned RegNo) {
317 case X86::EAX: case X86::AX: case X86::AL: return N86::EAX;
318 case X86::ECX: case X86::CX: case X86::CL: return N86::ECX;
319 case X86::EDX: case X86::DX: case X86::DL: return N86::EDX;
320 case X86::EBX: case X86::BX: case X86::BL: return N86::EBX;
321 case X86::ESP: case X86::SP: case X86::AH: return N86::ESP;
322 case X86::EBP: case X86::BP: case X86::CH: return N86::EBP;
323 case X86::ESI: case X86::SI: case X86::DH: return N86::ESI;
324 case X86::EDI: case X86::DI: case X86::BH: return N86::EDI;
326 case X86::ST0: case X86::ST1: case X86::ST2: case X86::ST3:
327 case X86::ST4: case X86::ST5: case X86::ST6: case X86::ST7:
328 return RegNo-X86::ST0;
330 assert(RegNo >= MRegisterInfo::FirstVirtualRegister &&
331 "Unknown physical register!");
332 assert(0 && "Register allocator hasn't allocated reg correctly yet!");
337 inline static unsigned char ModRMByte(unsigned Mod, unsigned RegOpcode,
339 assert(Mod < 4 && RegOpcode < 8 && RM < 8 && "ModRM Fields out of range!");
340 return RM | (RegOpcode << 3) | (Mod << 6);
343 void Emitter::emitRegModRMByte(unsigned ModRMReg, unsigned RegOpcodeFld){
344 MCE.emitByte(ModRMByte(3, RegOpcodeFld, getX86RegNum(ModRMReg)));
347 void Emitter::emitSIBByte(unsigned SS, unsigned Index, unsigned Base) {
348 // SIB byte is in the same format as the ModRMByte...
349 MCE.emitByte(ModRMByte(SS, Index, Base));
352 void Emitter::emitConstant(unsigned Val, unsigned Size) {
353 // Output the constant in little endian byte order...
354 for (unsigned i = 0; i != Size; ++i) {
355 MCE.emitByte(Val & 255);
360 static bool isDisp8(int Value) {
361 return Value == (signed char)Value;
364 void Emitter::emitMemModRMByte(const MachineInstr &MI,
365 unsigned Op, unsigned RegOpcodeField) {
366 const MachineOperand &Disp = MI.getOperand(Op+3);
367 if (MI.getOperand(Op).isConstantPoolIndex()) {
368 // Emit a direct address reference [disp32] where the displacement of the
369 // constant pool entry is controlled by the MCE.
370 MCE.emitByte(ModRMByte(0, RegOpcodeField, 5));
371 unsigned Index = MI.getOperand(Op).getConstantPoolIndex();
372 unsigned Address = MCE.getConstantPoolEntryAddress(Index);
373 MCE.emitWord(Address+Disp.getImmedValue());
377 const MachineOperand &BaseReg = MI.getOperand(Op);
378 const MachineOperand &Scale = MI.getOperand(Op+1);
379 const MachineOperand &IndexReg = MI.getOperand(Op+2);
381 // Is a SIB byte needed?
382 if (IndexReg.getReg() == 0 && BaseReg.getReg() != X86::ESP) {
383 if (BaseReg.getReg() == 0) { // Just a displacement?
384 // Emit special case [disp32] encoding
385 MCE.emitByte(ModRMByte(0, RegOpcodeField, 5));
386 emitConstant(Disp.getImmedValue(), 4);
388 unsigned BaseRegNo = getX86RegNum(BaseReg.getReg());
389 if (Disp.getImmedValue() == 0 && BaseRegNo != N86::EBP) {
390 // Emit simple indirect register encoding... [EAX] f.e.
391 MCE.emitByte(ModRMByte(0, RegOpcodeField, BaseRegNo));
392 } else if (isDisp8(Disp.getImmedValue())) {
393 // Emit the disp8 encoding... [REG+disp8]
394 MCE.emitByte(ModRMByte(1, RegOpcodeField, BaseRegNo));
395 emitConstant(Disp.getImmedValue(), 1);
397 // Emit the most general non-SIB encoding: [REG+disp32]
398 MCE.emitByte(ModRMByte(2, RegOpcodeField, BaseRegNo));
399 emitConstant(Disp.getImmedValue(), 4);
403 } else { // We need a SIB byte, so start by outputting the ModR/M byte first
404 assert(IndexReg.getReg() != X86::ESP && "Cannot use ESP as index reg!");
406 bool ForceDisp32 = false;
407 bool ForceDisp8 = false;
408 if (BaseReg.getReg() == 0) {
409 // If there is no base register, we emit the special case SIB byte with
410 // MOD=0, BASE=5, to JUST get the index, scale, and displacement.
411 MCE.emitByte(ModRMByte(0, RegOpcodeField, 4));
413 } else if (Disp.getImmedValue() == 0 && BaseReg.getReg() != X86::EBP) {
414 // Emit no displacement ModR/M byte
415 MCE.emitByte(ModRMByte(0, RegOpcodeField, 4));
416 } else if (isDisp8(Disp.getImmedValue())) {
417 // Emit the disp8 encoding...
418 MCE.emitByte(ModRMByte(1, RegOpcodeField, 4));
419 ForceDisp8 = true; // Make sure to force 8 bit disp if Base=EBP
421 // Emit the normal disp32 encoding...
422 MCE.emitByte(ModRMByte(2, RegOpcodeField, 4));
425 // Calculate what the SS field value should be...
426 static const unsigned SSTable[] = { ~0, 0, 1, ~0, 2, ~0, ~0, ~0, 3 };
427 unsigned SS = SSTable[Scale.getImmedValue()];
429 if (BaseReg.getReg() == 0) {
430 // Handle the SIB byte for the case where there is no base. The
431 // displacement has already been output.
432 assert(IndexReg.getReg() && "Index register must be specified!");
433 emitSIBByte(SS, getX86RegNum(IndexReg.getReg()), 5);
435 unsigned BaseRegNo = getX86RegNum(BaseReg.getReg());
437 if (IndexReg.getReg())
438 IndexRegNo = getX86RegNum(IndexReg.getReg());
440 IndexRegNo = 4; // For example [ESP+1*<noreg>+4]
441 emitSIBByte(SS, IndexRegNo, BaseRegNo);
444 // Do we need to output a displacement?
445 if (Disp.getImmedValue() != 0 || ForceDisp32 || ForceDisp8) {
446 if (!ForceDisp32 && isDisp8(Disp.getImmedValue()))
447 emitConstant(Disp.getImmedValue(), 1);
449 emitConstant(Disp.getImmedValue(), 4);
454 static unsigned sizeOfPtr(const TargetInstrDescriptor &Desc) {
455 switch (Desc.TSFlags & X86II::ArgMask) {
456 case X86II::Arg8: return 1;
457 case X86II::Arg16: return 2;
458 case X86II::Arg32: return 4;
459 case X86II::ArgF32: return 4;
460 case X86II::ArgF64: return 8;
461 case X86II::ArgF80: return 10;
462 default: assert(0 && "Memory size not set!");
467 void Emitter::emitInstruction(MachineInstr &MI) {
468 NumEmitted++; // Keep track of the # of mi's emitted
470 unsigned Opcode = MI.getOpcode();
471 const TargetInstrDescriptor &Desc = II->get(Opcode);
473 // Emit the repeat opcode prefix as needed.
474 if ((Desc.TSFlags & X86II::Op0Mask) == X86II::REP) MCE.emitByte(0xF3);
476 // Emit instruction prefixes if necessary
477 if (Desc.TSFlags & X86II::OpSize) MCE.emitByte(0x66);// Operand size...
479 switch (Desc.TSFlags & X86II::Op0Mask) {
481 MCE.emitByte(0x0F); // Two-byte opcode prefix
483 case X86II::REP: break; // already handled.
484 case X86II::D8: case X86II::D9: case X86II::DA: case X86II::DB:
485 case X86II::DC: case X86II::DD: case X86II::DE: case X86II::DF:
487 (((Desc.TSFlags & X86II::Op0Mask)-X86II::D8)
488 >> X86II::Op0Shift));
489 break; // Two-byte opcode prefix
490 default: assert(0 && "Invalid prefix!");
491 case 0: break; // No prefix!
494 unsigned char BaseOpcode = II->getBaseOpcodeFor(Opcode);
495 switch (Desc.TSFlags & X86II::FormMask) {
496 default: assert(0 && "Unknown FormMask value in X86 MachineCodeEmitter!");
498 if (Opcode != X86::IMPLICIT_USE &&
499 Opcode != X86::IMPLICIT_DEF &&
500 Opcode != X86::FP_REG_KILL)
501 std::cerr << "X86 Machine Code Emitter: No 'form', not emitting: " << MI;
505 MCE.emitByte(BaseOpcode);
506 if (MI.getNumOperands() == 1) {
507 MachineOperand &MO = MI.getOperand(0);
508 if (MO.isPCRelativeDisp()) {
509 // Conditional branch... FIXME: this should use an MBB destination!
510 emitPCRelativeBlockAddress(cast<BasicBlock>(MO.getVRegValue()));
511 } else if (MO.isGlobalAddress()) {
512 assert(MO.isPCRelative() && "Call target is not PC Relative?");
513 emitGlobalAddressForCall(MO.getGlobal());
514 } else if (MO.isExternalSymbol()) {
515 unsigned Address = MCE.getGlobalValueAddress(MO.getSymbolName());
516 assert(Address && "Unknown external symbol!");
517 emitMaybePCRelativeValue(Address, MO.isPCRelative());
519 assert(0 && "Unknown RawFrm operand!");
524 case X86II::AddRegFrm:
525 MCE.emitByte(BaseOpcode + getX86RegNum(MI.getOperand(0).getReg()));
526 if (MI.getNumOperands() == 2) {
527 MachineOperand &MO1 = MI.getOperand(1);
528 if (MO1.isImmediate() || MO1.getVRegValueOrNull() ||
529 MO1.isGlobalAddress() || MO1.isExternalSymbol()) {
530 unsigned Size = sizeOfPtr(Desc);
531 if (Value *V = MO1.getVRegValueOrNull()) {
532 assert(Size == 4 && "Don't know how to emit non-pointer values!");
533 emitGlobalAddressForPtr(cast<GlobalValue>(V));
534 } else if (MO1.isGlobalAddress()) {
535 assert(Size == 4 && "Don't know how to emit non-pointer values!");
536 assert(!MO1.isPCRelative() && "Function pointer ref is PC relative?");
537 emitGlobalAddressForPtr(MO1.getGlobal());
538 } else if (MO1.isExternalSymbol()) {
539 assert(Size == 4 && "Don't know how to emit non-pointer values!");
541 unsigned Address = MCE.getGlobalValueAddress(MO1.getSymbolName());
542 assert(Address && "Unknown external symbol!");
543 emitMaybePCRelativeValue(Address, MO1.isPCRelative());
545 emitConstant(MO1.getImmedValue(), Size);
551 case X86II::MRMDestReg: {
552 MCE.emitByte(BaseOpcode);
553 emitRegModRMByte(MI.getOperand(0).getReg(),
554 getX86RegNum(MI.getOperand(1).getReg()));
555 if (MI.getNumOperands() == 3)
556 emitConstant(MI.getOperand(2).getImmedValue(), sizeOfPtr(Desc));
559 case X86II::MRMDestMem:
560 MCE.emitByte(BaseOpcode);
561 emitMemModRMByte(MI, 0, getX86RegNum(MI.getOperand(4).getReg()));
564 case X86II::MRMSrcReg:
565 MCE.emitByte(BaseOpcode);
567 emitRegModRMByte(MI.getOperand(1).getReg(),
568 getX86RegNum(MI.getOperand(0).getReg()));
569 if (MI.getNumOperands() == 3)
570 emitConstant(MI.getOperand(2).getImmedValue(), sizeOfPtr(Desc));
573 case X86II::MRMSrcMem:
574 MCE.emitByte(BaseOpcode);
575 emitMemModRMByte(MI, MI.getNumOperands()-4,
576 getX86RegNum(MI.getOperand(0).getReg()));
579 case X86II::MRMS0r: case X86II::MRMS1r:
580 case X86II::MRMS2r: case X86II::MRMS3r:
581 case X86II::MRMS4r: case X86II::MRMS5r:
582 case X86II::MRMS6r: case X86II::MRMS7r:
583 MCE.emitByte(BaseOpcode);
584 emitRegModRMByte(MI.getOperand(0).getReg(),
585 (Desc.TSFlags & X86II::FormMask)-X86II::MRMS0r);
587 if (MI.getOperand(MI.getNumOperands()-1).isImmediate()) {
588 unsigned Size = sizeOfPtr(Desc);
589 emitConstant(MI.getOperand(MI.getNumOperands()-1).getImmedValue(), Size);
593 case X86II::MRMS0m: case X86II::MRMS1m:
594 case X86II::MRMS2m: case X86II::MRMS3m:
595 case X86II::MRMS4m: case X86II::MRMS5m:
596 case X86II::MRMS6m: case X86II::MRMS7m:
597 MCE.emitByte(BaseOpcode);
598 emitMemModRMByte(MI, 0, (Desc.TSFlags & X86II::FormMask)-X86II::MRMS0m);
600 if (MI.getNumOperands() == 5) {
601 unsigned Size = sizeOfPtr(Desc);
602 emitConstant(MI.getOperand(4).getImmedValue(), Size);