1 //===-- AsmPrinterInlineAsm.cpp - AsmPrinter Inline Asm Handling ----------===//
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 inline assembler pieces of the AsmPrinter class.
10 //
11 //===----------------------------------------------------------------------===//
12 
13 #include "llvm/ADT/SmallString.h"
14 #include "llvm/ADT/SmallVector.h"
15 #include "llvm/ADT/Twine.h"
16 #include "llvm/CodeGen/AsmPrinter.h"
17 #include "llvm/CodeGen/MachineBasicBlock.h"
18 #include "llvm/CodeGen/MachineFunction.h"
19 #include "llvm/CodeGen/MachineModuleInfo.h"
20 #include "llvm/CodeGen/TargetInstrInfo.h"
21 #include "llvm/CodeGen/TargetRegisterInfo.h"
22 #include "llvm/IR/Constants.h"
23 #include "llvm/IR/DataLayout.h"
24 #include "llvm/IR/DiagnosticInfo.h"
25 #include "llvm/IR/InlineAsm.h"
26 #include "llvm/IR/LLVMContext.h"
27 #include "llvm/IR/Module.h"
28 #include "llvm/MC/MCAsmInfo.h"
29 #include "llvm/MC/MCParser/MCTargetAsmParser.h"
30 #include "llvm/MC/MCStreamer.h"
31 #include "llvm/MC/MCSubtargetInfo.h"
32 #include "llvm/MC/MCSymbol.h"
33 #include "llvm/Support/ErrorHandling.h"
34 #include "llvm/Support/MemoryBuffer.h"
35 #include "llvm/Support/SourceMgr.h"
36 #include "llvm/Support/TargetRegistry.h"
37 #include "llvm/Support/raw_ostream.h"
38 #include "llvm/Target/TargetMachine.h"
39 using namespace llvm;
40 
41 #define DEBUG_TYPE "asm-printer"
42 
43 unsigned AsmPrinter::addInlineAsmDiagBuffer(StringRef AsmStr,
44                                             const MDNode *LocMDNode) const {
45   MCContext &Context = MMI->getContext();
46   Context.initInlineSourceManager();
47   SourceMgr &SrcMgr = *Context.getInlineSourceManager();
48   std::vector<const MDNode *> &LocInfos = Context.getLocInfos();
49 
50   std::unique_ptr<MemoryBuffer> Buffer;
51   // The inline asm source manager will outlive AsmStr, so make a copy of the
52   // string for SourceMgr to own.
53   Buffer = MemoryBuffer::getMemBufferCopy(AsmStr, "<inline asm>");
54 
55   // Tell SrcMgr about this buffer, it takes ownership of the buffer.
56   unsigned BufNum = SrcMgr.AddNewSourceBuffer(std::move(Buffer), SMLoc());
57 
58   // Store LocMDNode in DiagInfo, using BufNum as an identifier.
59   if (LocMDNode) {
60     LocInfos.resize(BufNum);
61     LocInfos[BufNum - 1] = LocMDNode;
62   }
63 
64   return BufNum;
65 }
66 
67 
68 /// EmitInlineAsm - Emit a blob of inline asm to the output streamer.
69 void AsmPrinter::emitInlineAsm(StringRef Str, const MCSubtargetInfo &STI,
70                                const MCTargetOptions &MCOptions,
71                                const MDNode *LocMDNode,
72                                InlineAsm::AsmDialect Dialect) const {
73   assert(!Str.empty() && "Can't emit empty inline asm block");
74 
75   // Remember if the buffer is nul terminated or not so we can avoid a copy.
76   bool isNullTerminated = Str.back() == 0;
77   if (isNullTerminated)
78     Str = Str.substr(0, Str.size()-1);
79 
80   // If the output streamer does not have mature MC support or the integrated
81   // assembler has been disabled or not required, just emit the blob textually.
82   // Otherwise parse the asm and emit it via MC support.
83   // This is useful in case the asm parser doesn't handle something but the
84   // system assembler does.
85   const MCAsmInfo *MCAI = TM.getMCAsmInfo();
86   assert(MCAI && "No MCAsmInfo");
87   if (!MCAI->useIntegratedAssembler() &&
88       !MCAI->parseInlineAsmUsingAsmParser() &&
89       !OutStreamer->isIntegratedAssemblerRequired()) {
90     emitInlineAsmStart();
91     OutStreamer->emitRawText(Str);
92     emitInlineAsmEnd(STI, nullptr);
93     return;
94   }
95 
96   unsigned BufNum = addInlineAsmDiagBuffer(Str, LocMDNode);
97   SourceMgr &SrcMgr = *MMI->getContext().getInlineSourceManager();
98   SrcMgr.setIncludeDirs(MCOptions.IASSearchPaths);
99 
100   std::unique_ptr<MCAsmParser> Parser(
101       createMCAsmParser(SrcMgr, OutContext, *OutStreamer, *MAI, BufNum));
102 
103   // Do not use assembler-level information for parsing inline assembly.
104   OutStreamer->setUseAssemblerInfoForParsing(false);
105 
106   // We create a new MCInstrInfo here since we might be at the module level
107   // and not have a MachineFunction to initialize the TargetInstrInfo from and
108   // we only need MCInstrInfo for asm parsing. We create one unconditionally
109   // because it's not subtarget dependent.
110   std::unique_ptr<MCInstrInfo> MII(TM.getTarget().createMCInstrInfo());
111   assert(MII && "Failed to create instruction info");
112   std::unique_ptr<MCTargetAsmParser> TAP(TM.getTarget().createMCAsmParser(
113       STI, *Parser, *MII, MCOptions));
114   if (!TAP)
115     report_fatal_error("Inline asm not supported by this streamer because"
116                        " we don't have an asm parser for this target\n");
117   Parser->setAssemblerDialect(Dialect);
118   Parser->setTargetParser(*TAP.get());
119   // Enable lexing Masm binary and hex integer literals in intel inline
120   // assembly.
121   if (Dialect == InlineAsm::AD_Intel)
122     Parser->getLexer().setLexMasmIntegers(true);
123 
124   emitInlineAsmStart();
125   // Don't implicitly switch to the text section before the asm.
126   (void)Parser->Run(/*NoInitialTextSection*/ true,
127                     /*NoFinalize*/ true);
128   emitInlineAsmEnd(STI, &TAP->getSTI());
129 }
130 
131 static void EmitMSInlineAsmStr(const char *AsmStr, const MachineInstr *MI,
132                                MachineModuleInfo *MMI, AsmPrinter *AP,
133                                uint64_t LocCookie, raw_ostream &OS) {
134   // Switch to the inline assembly variant.
135   OS << "\t.intel_syntax\n\t";
136 
137   const char *LastEmitted = AsmStr; // One past the last character emitted.
138   unsigned NumOperands = MI->getNumOperands();
139 
140   while (*LastEmitted) {
141     switch (*LastEmitted) {
142     default: {
143       // Not a special case, emit the string section literally.
144       const char *LiteralEnd = LastEmitted+1;
145       while (*LiteralEnd && *LiteralEnd != '{' && *LiteralEnd != '|' &&
146              *LiteralEnd != '}' && *LiteralEnd != '$' && *LiteralEnd != '\n')
147         ++LiteralEnd;
148 
149       OS.write(LastEmitted, LiteralEnd-LastEmitted);
150       LastEmitted = LiteralEnd;
151       break;
152     }
153     case '\n':
154       ++LastEmitted;   // Consume newline character.
155       OS << '\n';      // Indent code with newline.
156       break;
157     case '$': {
158       ++LastEmitted;   // Consume '$' character.
159       bool Done = true;
160 
161       // Handle escapes.
162       switch (*LastEmitted) {
163       default: Done = false; break;
164       case '$':
165         ++LastEmitted;  // Consume second '$' character.
166         break;
167       }
168       if (Done) break;
169 
170       bool HasCurlyBraces = false;
171       if (*LastEmitted == '{') {     // ${variable}
172         ++LastEmitted;               // Consume '{' character.
173         HasCurlyBraces = true;
174       }
175 
176       // If we have ${:foo}, then this is not a real operand reference, it is a
177       // "magic" string reference, just like in .td files.  Arrange to call
178       // PrintSpecial.
179       if (HasCurlyBraces && LastEmitted[0] == ':') {
180         ++LastEmitted;
181         const char *StrStart = LastEmitted;
182         const char *StrEnd = strchr(StrStart, '}');
183         if (!StrEnd)
184           report_fatal_error("Unterminated ${:foo} operand in inline asm"
185                              " string: '" + Twine(AsmStr) + "'");
186 
187         std::string Val(StrStart, StrEnd);
188         AP->PrintSpecial(MI, OS, Val.c_str());
189         LastEmitted = StrEnd+1;
190         break;
191       }
192 
193       const char *IDStart = LastEmitted;
194       const char *IDEnd = IDStart;
195       while (isDigit(*IDEnd))
196         ++IDEnd;
197 
198       unsigned Val;
199       if (StringRef(IDStart, IDEnd-IDStart).getAsInteger(10, Val))
200         report_fatal_error("Bad $ operand number in inline asm string: '" +
201                            Twine(AsmStr) + "'");
202       LastEmitted = IDEnd;
203 
204       if (Val >= NumOperands-1)
205         report_fatal_error("Invalid $ operand number in inline asm string: '" +
206                            Twine(AsmStr) + "'");
207 
208       char Modifier[2] = { 0, 0 };
209 
210       if (HasCurlyBraces) {
211         // If we have curly braces, check for a modifier character.  This
212         // supports syntax like ${0:u}, which correspond to "%u0" in GCC asm.
213         if (*LastEmitted == ':') {
214           ++LastEmitted;    // Consume ':' character.
215           if (*LastEmitted == 0)
216             report_fatal_error("Bad ${:} expression in inline asm string: '" +
217                                Twine(AsmStr) + "'");
218 
219           Modifier[0] = *LastEmitted;
220           ++LastEmitted;    // Consume modifier character.
221         }
222 
223         if (*LastEmitted != '}')
224           report_fatal_error("Bad ${} expression in inline asm string: '" +
225                              Twine(AsmStr) + "'");
226         ++LastEmitted;    // Consume '}' character.
227       }
228 
229       // Okay, we finally have a value number.  Ask the target to print this
230       // operand!
231       unsigned OpNo = InlineAsm::MIOp_FirstOperand;
232 
233       bool Error = false;
234 
235       // Scan to find the machine operand number for the operand.
236       for (; Val; --Val) {
237         if (OpNo >= MI->getNumOperands()) break;
238         unsigned OpFlags = MI->getOperand(OpNo).getImm();
239         OpNo += InlineAsm::getNumOperandRegisters(OpFlags) + 1;
240       }
241 
242       // We may have a location metadata attached to the end of the
243       // instruction, and at no point should see metadata at any
244       // other point while processing. It's an error if so.
245       if (OpNo >= MI->getNumOperands() ||
246           MI->getOperand(OpNo).isMetadata()) {
247         Error = true;
248       } else {
249         unsigned OpFlags = MI->getOperand(OpNo).getImm();
250         ++OpNo;  // Skip over the ID number.
251 
252         if (InlineAsm::isMemKind(OpFlags)) {
253           Error = AP->PrintAsmMemoryOperand(
254               MI, OpNo, Modifier[0] ? Modifier : nullptr, OS);
255         } else {
256           Error = AP->PrintAsmOperand(MI, OpNo,
257                                       Modifier[0] ? Modifier : nullptr, OS);
258         }
259       }
260       if (Error) {
261         std::string msg;
262         raw_string_ostream Msg(msg);
263         Msg << "invalid operand in inline asm: '" << AsmStr << "'";
264         MMI->getModule()->getContext().emitError(LocCookie, Msg.str());
265       }
266       break;
267     }
268     }
269   }
270   OS << "\n\t.att_syntax\n" << (char)0;  // null terminate string.
271 }
272 
273 static void EmitGCCInlineAsmStr(const char *AsmStr, const MachineInstr *MI,
274                                 MachineModuleInfo *MMI, const MCAsmInfo *MAI,
275                                 AsmPrinter *AP, uint64_t LocCookie,
276                                 raw_ostream &OS) {
277   int CurVariant = -1;            // The number of the {.|.|.} region we are in.
278   const char *LastEmitted = AsmStr; // One past the last character emitted.
279   unsigned NumOperands = MI->getNumOperands();
280   int AsmPrinterVariant = MAI->getAssemblerDialect();
281 
282   if (MAI->getEmitGNUAsmStartIndentationMarker())
283     OS << '\t';
284 
285   while (*LastEmitted) {
286     switch (*LastEmitted) {
287     default: {
288       // Not a special case, emit the string section literally.
289       const char *LiteralEnd = LastEmitted+1;
290       while (*LiteralEnd && *LiteralEnd != '{' && *LiteralEnd != '|' &&
291              *LiteralEnd != '}' && *LiteralEnd != '$' && *LiteralEnd != '\n')
292         ++LiteralEnd;
293       if (CurVariant == -1 || CurVariant == AsmPrinterVariant)
294         OS.write(LastEmitted, LiteralEnd-LastEmitted);
295       LastEmitted = LiteralEnd;
296       break;
297     }
298     case '\n':
299       ++LastEmitted;   // Consume newline character.
300       OS << '\n';      // Indent code with newline.
301       break;
302     case '$': {
303       ++LastEmitted;   // Consume '$' character.
304       bool Done = true;
305 
306       // Handle escapes.
307       switch (*LastEmitted) {
308       default: Done = false; break;
309       case '$':     // $$ -> $
310         if (CurVariant == -1 || CurVariant == AsmPrinterVariant)
311           OS << '$';
312         ++LastEmitted;  // Consume second '$' character.
313         break;
314       case '(':             // $( -> same as GCC's { character.
315         ++LastEmitted;      // Consume '(' character.
316         if (CurVariant != -1)
317           report_fatal_error("Nested variants found in inline asm string: '" +
318                              Twine(AsmStr) + "'");
319         CurVariant = 0;     // We're in the first variant now.
320         break;
321       case '|':
322         ++LastEmitted;  // consume '|' character.
323         if (CurVariant == -1)
324           OS << '|';       // this is gcc's behavior for | outside a variant
325         else
326           ++CurVariant;   // We're in the next variant.
327         break;
328       case ')':         // $) -> same as GCC's } char.
329         ++LastEmitted;  // consume ')' character.
330         if (CurVariant == -1)
331           OS << '}';     // this is gcc's behavior for } outside a variant
332         else
333           CurVariant = -1;
334         break;
335       }
336       if (Done) break;
337 
338       bool HasCurlyBraces = false;
339       if (*LastEmitted == '{') {     // ${variable}
340         ++LastEmitted;               // Consume '{' character.
341         HasCurlyBraces = true;
342       }
343 
344       // If we have ${:foo}, then this is not a real operand reference, it is a
345       // "magic" string reference, just like in .td files.  Arrange to call
346       // PrintSpecial.
347       if (HasCurlyBraces && *LastEmitted == ':') {
348         ++LastEmitted;
349         const char *StrStart = LastEmitted;
350         const char *StrEnd = strchr(StrStart, '}');
351         if (!StrEnd)
352           report_fatal_error("Unterminated ${:foo} operand in inline asm"
353                              " string: '" + Twine(AsmStr) + "'");
354 
355         std::string Val(StrStart, StrEnd);
356         AP->PrintSpecial(MI, OS, Val.c_str());
357         LastEmitted = StrEnd+1;
358         break;
359       }
360 
361       const char *IDStart = LastEmitted;
362       const char *IDEnd = IDStart;
363       while (isDigit(*IDEnd))
364         ++IDEnd;
365 
366       unsigned Val;
367       if (StringRef(IDStart, IDEnd-IDStart).getAsInteger(10, Val))
368         report_fatal_error("Bad $ operand number in inline asm string: '" +
369                            Twine(AsmStr) + "'");
370       LastEmitted = IDEnd;
371 
372       char Modifier[2] = { 0, 0 };
373 
374       if (HasCurlyBraces) {
375         // If we have curly braces, check for a modifier character.  This
376         // supports syntax like ${0:u}, which correspond to "%u0" in GCC asm.
377         if (*LastEmitted == ':') {
378           ++LastEmitted;    // Consume ':' character.
379           if (*LastEmitted == 0)
380             report_fatal_error("Bad ${:} expression in inline asm string: '" +
381                                Twine(AsmStr) + "'");
382 
383           Modifier[0] = *LastEmitted;
384           ++LastEmitted;    // Consume modifier character.
385         }
386 
387         if (*LastEmitted != '}')
388           report_fatal_error("Bad ${} expression in inline asm string: '" +
389                              Twine(AsmStr) + "'");
390         ++LastEmitted;    // Consume '}' character.
391       }
392 
393       if (Val >= NumOperands-1)
394         report_fatal_error("Invalid $ operand number in inline asm string: '" +
395                            Twine(AsmStr) + "'");
396 
397       // Okay, we finally have a value number.  Ask the target to print this
398       // operand!
399       if (CurVariant == -1 || CurVariant == AsmPrinterVariant) {
400         unsigned OpNo = InlineAsm::MIOp_FirstOperand;
401 
402         bool Error = false;
403 
404         // Scan to find the machine operand number for the operand.
405         for (; Val; --Val) {
406           if (OpNo >= MI->getNumOperands()) break;
407           unsigned OpFlags = MI->getOperand(OpNo).getImm();
408           OpNo += InlineAsm::getNumOperandRegisters(OpFlags) + 1;
409         }
410 
411         // We may have a location metadata attached to the end of the
412         // instruction, and at no point should see metadata at any
413         // other point while processing. It's an error if so.
414         if (OpNo >= MI->getNumOperands() ||
415             MI->getOperand(OpNo).isMetadata()) {
416           Error = true;
417         } else {
418           unsigned OpFlags = MI->getOperand(OpNo).getImm();
419           ++OpNo;  // Skip over the ID number.
420 
421           // FIXME: Shouldn't arch-independent output template handling go into
422           // PrintAsmOperand?
423           // Labels are target independent.
424           if (MI->getOperand(OpNo).isBlockAddress()) {
425             const BlockAddress *BA = MI->getOperand(OpNo).getBlockAddress();
426             MCSymbol *Sym = AP->GetBlockAddressSymbol(BA);
427             Sym->print(OS, AP->MAI);
428             MMI->getContext().registerInlineAsmLabel(Sym);
429           } else if (MI->getOperand(OpNo).isMBB()) {
430             const MCSymbol *Sym = MI->getOperand(OpNo).getMBB()->getSymbol();
431             Sym->print(OS, AP->MAI);
432           } else if (Modifier[0] == 'l') {
433             Error = true;
434           } else if (InlineAsm::isMemKind(OpFlags)) {
435             Error = AP->PrintAsmMemoryOperand(
436                 MI, OpNo, Modifier[0] ? Modifier : nullptr, OS);
437           } else {
438             Error = AP->PrintAsmOperand(MI, OpNo,
439                                         Modifier[0] ? Modifier : nullptr, OS);
440           }
441         }
442         if (Error) {
443           std::string msg;
444           raw_string_ostream Msg(msg);
445           Msg << "invalid operand in inline asm: '" << AsmStr << "'";
446           MMI->getModule()->getContext().emitError(LocCookie, Msg.str());
447         }
448       }
449       break;
450     }
451     }
452   }
453   OS << '\n' << (char)0;  // null terminate string.
454 }
455 
456 /// This method formats and emits the specified machine instruction that is an
457 /// inline asm.
458 void AsmPrinter::emitInlineAsm(const MachineInstr *MI) const {
459   assert(MI->isInlineAsm() && "printInlineAsm only works on inline asms");
460 
461   // Count the number of register definitions to find the asm string.
462   unsigned NumDefs = 0;
463   for (; MI->getOperand(NumDefs).isReg() && MI->getOperand(NumDefs).isDef();
464        ++NumDefs)
465     assert(NumDefs != MI->getNumOperands()-2 && "No asm string?");
466 
467   assert(MI->getOperand(NumDefs).isSymbol() && "No asm string?");
468 
469   // Disassemble the AsmStr, printing out the literal pieces, the operands, etc.
470   const char *AsmStr = MI->getOperand(NumDefs).getSymbolName();
471 
472   // If this asmstr is empty, just print the #APP/#NOAPP markers.
473   // These are useful to see where empty asm's wound up.
474   if (AsmStr[0] == 0) {
475     OutStreamer->emitRawComment(MAI->getInlineAsmStart());
476     OutStreamer->emitRawComment(MAI->getInlineAsmEnd());
477     return;
478   }
479 
480   // Emit the #APP start marker.  This has to happen even if verbose-asm isn't
481   // enabled, so we use emitRawComment.
482   OutStreamer->emitRawComment(MAI->getInlineAsmStart());
483 
484   // Get the !srcloc metadata node if we have it, and decode the loc cookie from
485   // it.
486   uint64_t LocCookie = 0;
487   const MDNode *LocMD = nullptr;
488   for (unsigned i = MI->getNumOperands(); i != 0; --i) {
489     if (MI->getOperand(i-1).isMetadata() &&
490         (LocMD = MI->getOperand(i-1).getMetadata()) &&
491         LocMD->getNumOperands() != 0) {
492       if (const ConstantInt *CI =
493               mdconst::dyn_extract<ConstantInt>(LocMD->getOperand(0))) {
494         LocCookie = CI->getZExtValue();
495         break;
496       }
497     }
498   }
499 
500   // Emit the inline asm to a temporary string so we can emit it through
501   // EmitInlineAsm.
502   SmallString<256> StringData;
503   raw_svector_ostream OS(StringData);
504 
505   AsmPrinter *AP = const_cast<AsmPrinter*>(this);
506   if (MI->getInlineAsmDialect() == InlineAsm::AD_ATT)
507     EmitGCCInlineAsmStr(AsmStr, MI, MMI, MAI, AP, LocCookie, OS);
508   else
509     EmitMSInlineAsmStr(AsmStr, MI, MMI, AP, LocCookie, OS);
510 
511   // Emit warnings if we use reserved registers on the clobber list, as
512   // that might lead to undefined behaviour.
513   SmallVector<Register, 8> RestrRegs;
514   const TargetRegisterInfo *TRI = MF->getSubtarget().getRegisterInfo();
515   // Start with the first operand descriptor, and iterate over them.
516   for (unsigned I = InlineAsm::MIOp_FirstOperand, NumOps = MI->getNumOperands();
517        I < NumOps; ++I) {
518     const MachineOperand &MO = MI->getOperand(I);
519     if (!MO.isImm())
520       continue;
521     unsigned Flags = MO.getImm();
522     if (InlineAsm::getKind(Flags) == InlineAsm::Kind_Clobber) {
523       Register Reg = MI->getOperand(I + 1).getReg();
524       if (!TRI->isAsmClobberable(*MF, Reg))
525         RestrRegs.push_back(Reg);
526     }
527     // Skip to one before the next operand descriptor, if it exists.
528     I += InlineAsm::getNumOperandRegisters(Flags);
529   }
530 
531   if (!RestrRegs.empty()) {
532     std::string Msg = "inline asm clobber list contains reserved registers: ";
533     ListSeparator LS;
534     for (const Register &RR : RestrRegs) {
535       Msg += LS;
536       Msg += TRI->getName(RR);
537     }
538     const char *Note =
539         "Reserved registers on the clobber list may not be "
540         "preserved across the asm statement, and clobbering them may "
541         "lead to undefined behaviour.";
542     MMI->getModule()->getContext().diagnose(DiagnosticInfoInlineAsm(
543         LocCookie, Msg.c_str(), DiagnosticSeverity::DS_Warning));
544     MMI->getModule()->getContext().diagnose(
545         DiagnosticInfoInlineAsm(LocCookie, Note, DiagnosticSeverity::DS_Note));
546   }
547 
548   emitInlineAsm(OS.str(), getSubtargetInfo(), TM.Options.MCOptions, LocMD,
549                 MI->getInlineAsmDialect());
550 
551   // Emit the #NOAPP end marker.  This has to happen even if verbose-asm isn't
552   // enabled, so we use emitRawComment.
553   OutStreamer->emitRawComment(MAI->getInlineAsmEnd());
554 }
555 
556 /// PrintSpecial - Print information related to the specified machine instr
557 /// that is independent of the operand, and may be independent of the instr
558 /// itself.  This can be useful for portably encoding the comment character
559 /// or other bits of target-specific knowledge into the asmstrings.  The
560 /// syntax used is ${:comment}.  Targets can override this to add support
561 /// for their own strange codes.
562 void AsmPrinter::PrintSpecial(const MachineInstr *MI, raw_ostream &OS,
563                               const char *Code) const {
564   if (!strcmp(Code, "private")) {
565     const DataLayout &DL = MF->getDataLayout();
566     OS << DL.getPrivateGlobalPrefix();
567   } else if (!strcmp(Code, "comment")) {
568     OS << MAI->getCommentString();
569   } else if (!strcmp(Code, "uid")) {
570     // Comparing the address of MI isn't sufficient, because machineinstrs may
571     // be allocated to the same address across functions.
572 
573     // If this is a new LastFn instruction, bump the counter.
574     if (LastMI != MI || LastFn != getFunctionNumber()) {
575       ++Counter;
576       LastMI = MI;
577       LastFn = getFunctionNumber();
578     }
579     OS << Counter;
580   } else {
581     std::string msg;
582     raw_string_ostream Msg(msg);
583     Msg << "Unknown special formatter '" << Code
584          << "' for machine instr: " << *MI;
585     report_fatal_error(Msg.str());
586   }
587 }
588 
589 void AsmPrinter::PrintSymbolOperand(const MachineOperand &MO, raw_ostream &OS) {
590   assert(MO.isGlobal() && "caller should check MO.isGlobal");
591   getSymbolPreferLocal(*MO.getGlobal())->print(OS, MAI);
592   printOffset(MO.getOffset(), OS);
593 }
594 
595 /// PrintAsmOperand - Print the specified operand of MI, an INLINEASM
596 /// instruction, using the specified assembler variant.  Targets should
597 /// override this to format as appropriate for machine specific ExtraCodes
598 /// or when the arch-independent handling would be too complex otherwise.
599 bool AsmPrinter::PrintAsmOperand(const MachineInstr *MI, unsigned OpNo,
600                                  const char *ExtraCode, raw_ostream &O) {
601   // Does this asm operand have a single letter operand modifier?
602   if (ExtraCode && ExtraCode[0]) {
603     if (ExtraCode[1] != 0) return true; // Unknown modifier.
604 
605     // https://gcc.gnu.org/onlinedocs/gccint/Output-Template.html
606     const MachineOperand &MO = MI->getOperand(OpNo);
607     switch (ExtraCode[0]) {
608     default:
609       return true;  // Unknown modifier.
610     case 'a': // Print as memory address.
611       if (MO.isReg()) {
612         PrintAsmMemoryOperand(MI, OpNo, nullptr, O);
613         return false;
614       }
615       LLVM_FALLTHROUGH; // GCC allows '%a' to behave like '%c' with immediates.
616     case 'c': // Substitute immediate value without immediate syntax
617       if (MO.isImm()) {
618         O << MO.getImm();
619         return false;
620       }
621       if (MO.isGlobal()) {
622         PrintSymbolOperand(MO, O);
623         return false;
624       }
625       return true;
626     case 'n':  // Negate the immediate constant.
627       if (!MO.isImm())
628         return true;
629       O << -MO.getImm();
630       return false;
631     case 's':  // The GCC deprecated s modifier
632       if (!MO.isImm())
633         return true;
634       O << ((32 - MO.getImm()) & 31);
635       return false;
636     }
637   }
638   return true;
639 }
640 
641 bool AsmPrinter::PrintAsmMemoryOperand(const MachineInstr *MI, unsigned OpNo,
642                                        const char *ExtraCode, raw_ostream &O) {
643   // Target doesn't support this yet!
644   return true;
645 }
646 
647 void AsmPrinter::emitInlineAsmStart() const {}
648 
649 void AsmPrinter::emitInlineAsmEnd(const MCSubtargetInfo &StartInfo,
650                                   const MCSubtargetInfo *EndInfo) const {}
651