SemaStmtAsm.cpp revision e54cba1ec0b0e498ee67d200289035797932e714 
1//===--- SemaStmtAsm.cpp - Semantic Analysis for Asm Statements -----------===//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9//
10//  This file implements semantic analysis for inline asm statements.
11//
12//===----------------------------------------------------------------------===//
13
14#include "clang/Sema/SemaInternal.h"
15#include "clang/Sema/Scope.h"
16#include "clang/Sema/ScopeInfo.h"
17#include "clang/Sema/Initialization.h"
18#include "clang/Sema/Lookup.h"
19#include "clang/AST/TypeLoc.h"
20#include "clang/Lex/Preprocessor.h"
21#include "clang/Basic/TargetInfo.h"
22#include "llvm/ADT/ArrayRef.h"
23#include "llvm/ADT/BitVector.h"
24#include "llvm/ADT/SmallString.h"
25#include "llvm/MC/MCAsmInfo.h"
26#include "llvm/MC/MCContext.h"
27#include "llvm/MC/MCExpr.h"
28#include "llvm/MC/MCInst.h"
29#include "llvm/MC/MCInstPrinter.h"
30#include "llvm/MC/MCInstrInfo.h"
31#include "llvm/MC/MCObjectFileInfo.h"
32#include "llvm/MC/MCRegisterInfo.h"
33#include "llvm/MC/MCStreamer.h"
34#include "llvm/MC/MCSubtargetInfo.h"
35#include "llvm/MC/MCSymbol.h"
36#include "llvm/MC/MCTargetAsmParser.h"
37#include "llvm/MC/MCParser/MCAsmLexer.h"
38#include "llvm/MC/MCParser/MCAsmParser.h"
39#include "llvm/MC/MCParser/MCParsedAsmOperand.h"
40#include "llvm/Support/SourceMgr.h"
41#include "llvm/Support/TargetRegistry.h"
42#include "llvm/Support/TargetSelect.h"
43using namespace clang;
44using namespace sema;
45
46/// CheckAsmLValue - GNU C has an extremely ugly extension whereby they silently
47/// ignore "noop" casts in places where an lvalue is required by an inline asm.
48/// We emulate this behavior when -fheinous-gnu-extensions is specified, but
49/// provide a strong guidance to not use it.
50///
51/// This method checks to see if the argument is an acceptable l-value and
52/// returns false if it is a case we can handle.
53static bool CheckAsmLValue(const Expr *E, Sema &S) {
54  // Type dependent expressions will be checked during instantiation.
55  if (E->isTypeDependent())
56    return false;
57
58  if (E->isLValue())
59    return false;  // Cool, this is an lvalue.
60
61  // Okay, this is not an lvalue, but perhaps it is the result of a cast that we
62  // are supposed to allow.
63  const Expr *E2 = E->IgnoreParenNoopCasts(S.Context);
64  if (E != E2 && E2->isLValue()) {
65    if (!S.getLangOpts().HeinousExtensions)
66      S.Diag(E2->getLocStart(), diag::err_invalid_asm_cast_lvalue)
67        << E->getSourceRange();
68    else
69      S.Diag(E2->getLocStart(), diag::warn_invalid_asm_cast_lvalue)
70        << E->getSourceRange();
71    // Accept, even if we emitted an error diagnostic.
72    return false;
73  }
74
75  // None of the above, just randomly invalid non-lvalue.
76  return true;
77}
78
79/// isOperandMentioned - Return true if the specified operand # is mentioned
80/// anywhere in the decomposed asm string.
81static bool isOperandMentioned(unsigned OpNo,
82                         ArrayRef<GCCAsmStmt::AsmStringPiece> AsmStrPieces) {
83  for (unsigned p = 0, e = AsmStrPieces.size(); p != e; ++p) {
84    const GCCAsmStmt::AsmStringPiece &Piece = AsmStrPieces[p];
85    if (!Piece.isOperand()) continue;
86
87    // If this is a reference to the input and if the input was the smaller
88    // one, then we have to reject this asm.
89    if (Piece.getOperandNo() == OpNo)
90      return true;
91  }
92  return false;
93}
94
95StmtResult Sema::ActOnGCCAsmStmt(SourceLocation AsmLoc, bool IsSimple,
96                                 bool IsVolatile, unsigned NumOutputs,
97                                 unsigned NumInputs, IdentifierInfo **Names,
98                                 MultiExprArg constraints, MultiExprArg exprs,
99                                 Expr *asmString, MultiExprArg clobbers,
100                                 SourceLocation RParenLoc) {
101  unsigned NumClobbers = clobbers.size();
102  StringLiteral **Constraints =
103    reinterpret_cast<StringLiteral**>(constraints.data());
104  Expr **Exprs = exprs.data();
105  StringLiteral *AsmString = cast<StringLiteral>(asmString);
106  StringLiteral **Clobbers = reinterpret_cast<StringLiteral**>(clobbers.data());
107
108  SmallVector<TargetInfo::ConstraintInfo, 4> OutputConstraintInfos;
109
110  // The parser verifies that there is a string literal here.
111  if (!AsmString->isAscii())
112    return StmtError(Diag(AsmString->getLocStart(),diag::err_asm_wide_character)
113      << AsmString->getSourceRange());
114
115  for (unsigned i = 0; i != NumOutputs; i++) {
116    StringLiteral *Literal = Constraints[i];
117    if (!Literal->isAscii())
118      return StmtError(Diag(Literal->getLocStart(),diag::err_asm_wide_character)
119        << Literal->getSourceRange());
120
121    StringRef OutputName;
122    if (Names[i])
123      OutputName = Names[i]->getName();
124
125    TargetInfo::ConstraintInfo Info(Literal->getString(), OutputName);
126    if (!Context.getTargetInfo().validateOutputConstraint(Info))
127      return StmtError(Diag(Literal->getLocStart(),
128                            diag::err_asm_invalid_output_constraint)
129                       << Info.getConstraintStr());
130
131    // Check that the output exprs are valid lvalues.
132    Expr *OutputExpr = Exprs[i];
133    if (CheckAsmLValue(OutputExpr, *this)) {
134      return StmtError(Diag(OutputExpr->getLocStart(),
135                  diag::err_asm_invalid_lvalue_in_output)
136        << OutputExpr->getSourceRange());
137    }
138
139    OutputConstraintInfos.push_back(Info);
140  }
141
142  SmallVector<TargetInfo::ConstraintInfo, 4> InputConstraintInfos;
143
144  for (unsigned i = NumOutputs, e = NumOutputs + NumInputs; i != e; i++) {
145    StringLiteral *Literal = Constraints[i];
146    if (!Literal->isAscii())
147      return StmtError(Diag(Literal->getLocStart(),diag::err_asm_wide_character)
148        << Literal->getSourceRange());
149
150    StringRef InputName;
151    if (Names[i])
152      InputName = Names[i]->getName();
153
154    TargetInfo::ConstraintInfo Info(Literal->getString(), InputName);
155    if (!Context.getTargetInfo().validateInputConstraint(OutputConstraintInfos.data(),
156                                                NumOutputs, Info)) {
157      return StmtError(Diag(Literal->getLocStart(),
158                            diag::err_asm_invalid_input_constraint)
159                       << Info.getConstraintStr());
160    }
161
162    Expr *InputExpr = Exprs[i];
163
164    // Only allow void types for memory constraints.
165    if (Info.allowsMemory() && !Info.allowsRegister()) {
166      if (CheckAsmLValue(InputExpr, *this))
167        return StmtError(Diag(InputExpr->getLocStart(),
168                              diag::err_asm_invalid_lvalue_in_input)
169                         << Info.getConstraintStr()
170                         << InputExpr->getSourceRange());
171    }
172
173    if (Info.allowsRegister()) {
174      if (InputExpr->getType()->isVoidType()) {
175        return StmtError(Diag(InputExpr->getLocStart(),
176                              diag::err_asm_invalid_type_in_input)
177          << InputExpr->getType() << Info.getConstraintStr()
178          << InputExpr->getSourceRange());
179      }
180    }
181
182    ExprResult Result = DefaultFunctionArrayLvalueConversion(Exprs[i]);
183    if (Result.isInvalid())
184      return StmtError();
185
186    Exprs[i] = Result.take();
187    InputConstraintInfos.push_back(Info);
188  }
189
190  // Check that the clobbers are valid.
191  for (unsigned i = 0; i != NumClobbers; i++) {
192    StringLiteral *Literal = Clobbers[i];
193    if (!Literal->isAscii())
194      return StmtError(Diag(Literal->getLocStart(),diag::err_asm_wide_character)
195        << Literal->getSourceRange());
196
197    StringRef Clobber = Literal->getString();
198
199    if (!Context.getTargetInfo().isValidClobber(Clobber))
200      return StmtError(Diag(Literal->getLocStart(),
201                  diag::err_asm_unknown_register_name) << Clobber);
202  }
203
204  GCCAsmStmt *NS =
205    new (Context) GCCAsmStmt(Context, AsmLoc, IsSimple, IsVolatile, NumOutputs,
206                             NumInputs, Names, Constraints, Exprs, AsmString,
207                             NumClobbers, Clobbers, RParenLoc);
208  // Validate the asm string, ensuring it makes sense given the operands we
209  // have.
210  SmallVector<GCCAsmStmt::AsmStringPiece, 8> Pieces;
211  unsigned DiagOffs;
212  if (unsigned DiagID = NS->AnalyzeAsmString(Pieces, Context, DiagOffs)) {
213    Diag(getLocationOfStringLiteralByte(AsmString, DiagOffs), DiagID)
214           << AsmString->getSourceRange();
215    return StmtError();
216  }
217
218  // Validate tied input operands for type mismatches.
219  for (unsigned i = 0, e = InputConstraintInfos.size(); i != e; ++i) {
220    TargetInfo::ConstraintInfo &Info = InputConstraintInfos[i];
221
222    // If this is a tied constraint, verify that the output and input have
223    // either exactly the same type, or that they are int/ptr operands with the
224    // same size (int/long, int*/long, are ok etc).
225    if (!Info.hasTiedOperand()) continue;
226
227    unsigned TiedTo = Info.getTiedOperand();
228    unsigned InputOpNo = i+NumOutputs;
229    Expr *OutputExpr = Exprs[TiedTo];
230    Expr *InputExpr = Exprs[InputOpNo];
231
232    if (OutputExpr->isTypeDependent() || InputExpr->isTypeDependent())
233      continue;
234
235    QualType InTy = InputExpr->getType();
236    QualType OutTy = OutputExpr->getType();
237    if (Context.hasSameType(InTy, OutTy))
238      continue;  // All types can be tied to themselves.
239
240    // Decide if the input and output are in the same domain (integer/ptr or
241    // floating point.
242    enum AsmDomain {
243      AD_Int, AD_FP, AD_Other
244    } InputDomain, OutputDomain;
245
246    if (InTy->isIntegerType() || InTy->isPointerType())
247      InputDomain = AD_Int;
248    else if (InTy->isRealFloatingType())
249      InputDomain = AD_FP;
250    else
251      InputDomain = AD_Other;
252
253    if (OutTy->isIntegerType() || OutTy->isPointerType())
254      OutputDomain = AD_Int;
255    else if (OutTy->isRealFloatingType())
256      OutputDomain = AD_FP;
257    else
258      OutputDomain = AD_Other;
259
260    // They are ok if they are the same size and in the same domain.  This
261    // allows tying things like:
262    //   void* to int*
263    //   void* to int            if they are the same size.
264    //   double to long double   if they are the same size.
265    //
266    uint64_t OutSize = Context.getTypeSize(OutTy);
267    uint64_t InSize = Context.getTypeSize(InTy);
268    if (OutSize == InSize && InputDomain == OutputDomain &&
269        InputDomain != AD_Other)
270      continue;
271
272    // If the smaller input/output operand is not mentioned in the asm string,
273    // then we can promote the smaller one to a larger input and the asm string
274    // won't notice.
275    bool SmallerValueMentioned = false;
276
277    // If this is a reference to the input and if the input was the smaller
278    // one, then we have to reject this asm.
279    if (isOperandMentioned(InputOpNo, Pieces)) {
280      // This is a use in the asm string of the smaller operand.  Since we
281      // codegen this by promoting to a wider value, the asm will get printed
282      // "wrong".
283      SmallerValueMentioned |= InSize < OutSize;
284    }
285    if (isOperandMentioned(TiedTo, Pieces)) {
286      // If this is a reference to the output, and if the output is the larger
287      // value, then it's ok because we'll promote the input to the larger type.
288      SmallerValueMentioned |= OutSize < InSize;
289    }
290
291    // If the smaller value wasn't mentioned in the asm string, and if the
292    // output was a register, just extend the shorter one to the size of the
293    // larger one.
294    if (!SmallerValueMentioned && InputDomain != AD_Other &&
295        OutputConstraintInfos[TiedTo].allowsRegister())
296      continue;
297
298    // Either both of the operands were mentioned or the smaller one was
299    // mentioned.  One more special case that we'll allow: if the tied input is
300    // integer, unmentioned, and is a constant, then we'll allow truncating it
301    // down to the size of the destination.
302    if (InputDomain == AD_Int && OutputDomain == AD_Int &&
303        !isOperandMentioned(InputOpNo, Pieces) &&
304        InputExpr->isEvaluatable(Context)) {
305      CastKind castKind =
306        (OutTy->isBooleanType() ? CK_IntegralToBoolean : CK_IntegralCast);
307      InputExpr = ImpCastExprToType(InputExpr, OutTy, castKind).take();
308      Exprs[InputOpNo] = InputExpr;
309      NS->setInputExpr(i, InputExpr);
310      continue;
311    }
312
313    Diag(InputExpr->getLocStart(),
314         diag::err_asm_tying_incompatible_types)
315      << InTy << OutTy << OutputExpr->getSourceRange()
316      << InputExpr->getSourceRange();
317    return StmtError();
318  }
319
320  return Owned(NS);
321}
322
323// getSpelling - Get the spelling of the AsmTok token.
324static StringRef getSpelling(Sema &SemaRef, Token AsmTok) {
325  StringRef Asm;
326  SmallString<512> TokenBuf;
327  TokenBuf.resize(512);
328  bool StringInvalid = false;
329  Asm = SemaRef.PP.getSpelling(AsmTok, TokenBuf, &StringInvalid);
330  assert (!StringInvalid && "Expected valid string!");
331  return Asm;
332}
333
334// Build the inline assembly string.  Returns true on error.
335static bool buildMSAsmString(Sema &SemaRef,
336                             SourceLocation AsmLoc,
337                             ArrayRef<Token> AsmToks,
338                             std::string &AsmString) {
339  assert (!AsmToks.empty() && "Didn't expect an empty AsmToks!");
340
341  SmallString<512> Asm;
342  for (unsigned i = 0, e = AsmToks.size(); i < e; ++i) {
343    bool isNewAsm = ((i == 0) ||
344                     AsmToks[i].isAtStartOfLine() ||
345                     AsmToks[i].is(tok::kw_asm));
346    if (isNewAsm) {
347      if (i != 0)
348        Asm += "\n\t";
349
350      if (AsmToks[i].is(tok::kw_asm)) {
351        i++; // Skip __asm
352        if (i == e) {
353          SemaRef.Diag(AsmLoc, diag::err_asm_empty);
354          return true;
355        }
356
357      }
358    }
359
360    if (i && AsmToks[i].hasLeadingSpace() && !isNewAsm)
361      Asm += ' ';
362
363    StringRef Spelling = getSpelling(SemaRef, AsmToks[i]);
364    Asm += Spelling;
365  }
366  AsmString = Asm.str();
367  return false;
368}
369
370namespace {
371enum AsmOpRewriteKind {
372   AOK_Imm,
373   AOK_Input,
374   AOK_Output
375};
376
377struct AsmOpRewrite {
378  AsmOpRewriteKind Kind;
379  llvm::SMLoc Loc;
380  unsigned Len;
381
382public:
383  AsmOpRewrite(AsmOpRewriteKind kind, llvm::SMLoc loc, unsigned len)
384    : Kind(kind), Loc(loc), Len(len) { }
385};
386
387}
388
389StmtResult Sema::ActOnMSAsmStmt(SourceLocation AsmLoc, SourceLocation LBraceLoc,
390                                ArrayRef<Token> AsmToks,SourceLocation EndLoc) {
391  SmallVector<IdentifierInfo*, 4> Inputs;
392  SmallVector<IdentifierInfo*, 4> Outputs;
393  SmallVector<IdentifierInfo*, 4> Names;
394  SmallVector<std::string, 4> InputConstraints;
395  SmallVector<std::string, 4> OutputConstraints;
396  SmallVector<StringRef, 4> Constraints;
397  unsigned NumOutputs;
398  unsigned NumInputs;
399  SmallVector<Expr*, 4> InputExprs;
400  SmallVector<Expr*, 4> OutputExprs;
401  SmallVector<Expr*, 4> Exprs;
402  SmallVector<StringRef, 4> Clobbers;
403  std::set<std::string> ClobberRegs;
404
405  SmallVector<struct AsmOpRewrite, 4> AsmStrRewrites;
406
407  // Empty asm statements don't need to instantiate the AsmParser, etc.
408  if (AsmToks.empty()) {
409    StringRef EmptyAsmStr;
410    MSAsmStmt *NS =
411      new (Context) MSAsmStmt(Context, AsmLoc, LBraceLoc, /*IsSimple*/ true,
412                              /*IsVolatile*/ true, AsmToks, /*NumOutputs*/ 0,
413                              /*NumInputs*/ 0, Names, Constraints, Exprs, EmptyAsmStr,
414                              Clobbers, EndLoc);
415    return Owned(NS);
416  }
417
418  std::string AsmString;
419  if (buildMSAsmString(*this, AsmLoc, AsmToks, AsmString))
420    return StmtError();
421
422  // Get the target specific parser.
423  std::string Error;
424  const std::string &TT = Context.getTargetInfo().getTriple().getTriple();
425  const llvm::Target *TheTarget(llvm::TargetRegistry::lookupTarget(TT, Error));
426
427  OwningPtr<llvm::MCAsmInfo> MAI(TheTarget->createMCAsmInfo(TT));
428  OwningPtr<llvm::MCRegisterInfo> MRI(TheTarget->createMCRegInfo(TT));
429  OwningPtr<llvm::MCObjectFileInfo> MOFI(new llvm::MCObjectFileInfo());
430  OwningPtr<llvm::MCSubtargetInfo>
431    STI(TheTarget->createMCSubtargetInfo(TT, "", ""));
432
433  llvm::SourceMgr SrcMgr;
434  llvm::MCContext Ctx(*MAI, *MRI, MOFI.get(), &SrcMgr);
435  llvm::MemoryBuffer *Buffer =
436    llvm::MemoryBuffer::getMemBuffer(AsmString, "<inline asm>");
437
438  // Tell SrcMgr about this buffer, which is what the parser will pick up.
439  SrcMgr.AddNewSourceBuffer(Buffer, llvm::SMLoc());
440
441  OwningPtr<llvm::MCStreamer> Str(createNullStreamer(Ctx));
442  OwningPtr<llvm::MCAsmParser>
443    Parser(createMCAsmParser(SrcMgr, Ctx, *Str.get(), *MAI));
444  OwningPtr<llvm::MCTargetAsmParser>
445    TargetParser(TheTarget->createMCAsmParser(*STI, *Parser));
446    Parser->setParsingInlineAsm(true);
447
448  // Get the instruction descriptor.
449  const llvm::MCInstrInfo *MII = TheTarget->createMCInstrInfo();
450  llvm::MCInstPrinter *IP =
451    TheTarget->createMCInstPrinter(1, *MAI, *MII, *MRI, *STI);
452
453  // Change to the Intel dialect.
454  Parser->setAssemblerDialect(1);
455  Parser->setTargetParser(*TargetParser.get());
456  Parser->setParsingInlineAsm(true);
457
458  // Prime the lexer.
459  Parser->Lex();
460
461  // While we have input, parse each statement.
462  unsigned InputIdx = 0;
463  unsigned OutputIdx = 0;
464  while (Parser->getLexer().isNot(llvm::AsmToken::Eof)) {
465    if (Parser->ParseStatement()) {
466      // FIXME: The AsmParser should report errors, but we could potentially be
467      // more verbose here.
468      break;
469    }
470
471    if (Parser->isInstruction()) {
472      const llvm::MCInstrDesc &Desc = MII->get(Parser->getOpcode());
473
474      // Build the list of clobbers, outputs and inputs.
475      for (unsigned i = 1, e = Parser->getNumParsedOperands(); i != e; ++i) {
476        llvm::MCParsedAsmOperand &Operand = Parser->getParsedOperand(i);
477
478        // Immediate.
479        if (Operand.isImm()) {
480          AsmStrRewrites.push_back(AsmOpRewrite(AOK_Imm,
481                                                Operand.getStartLoc(),
482                                                Operand.getNameLen()));
483          continue;
484        }
485
486
487        // Register operand.
488        if (Operand.isReg()) {
489          unsigned NumDefs = Desc.getNumDefs();
490          // Clobber.
491          if (NumDefs && Operand.getMCOperandNum() < NumDefs) {
492            std::string Reg;
493            llvm::raw_string_ostream OS(Reg);
494            IP->printRegName(OS, Operand.getReg());
495            StringRef Clobber(OS.str());
496            if (!Context.getTargetInfo().isValidClobber(Clobber))
497              return StmtError(
498                Diag(AsmLoc, diag::err_asm_unknown_register_name) << Clobber);
499            ClobberRegs.insert(Reg);
500          }
501          continue;
502        }
503
504
505        // Expr/Input or Output.
506        StringRef Name = Operand.getName();
507        if (IdentifierInfo *II = &Context.Idents.get(Name)) {
508          CXXScopeSpec SS;
509          UnqualifiedId Id;
510          SourceLocation Loc;
511          Id.setIdentifier(II, AsmLoc);
512          ExprResult Result = ActOnIdExpression(getCurScope(), SS, Loc, Id,
513                                                false, false);
514          if (!Result.isInvalid()) {
515            bool isOutput = (i == 1) && Desc.mayStore();
516            if (isOutput) {
517              std::string Constraint = "=";
518              ++InputIdx;
519              Outputs.push_back(II);
520              OutputExprs.push_back(Result.take());
521              Constraint += Operand.getConstraint().str();
522              OutputConstraints.push_back(Constraint);
523              AsmStrRewrites.push_back(AsmOpRewrite(AOK_Output,
524                                                    Operand.getStartLoc(),
525                                                    Operand.getNameLen()));
526            } else {
527              Inputs.push_back(II);
528              InputExprs.push_back(Result.take());
529              InputConstraints.push_back(Operand.getConstraint().str());
530              AsmStrRewrites.push_back(AsmOpRewrite(AOK_Input,
531                                                    Operand.getStartLoc(),
532                                                    Operand.getNameLen()));
533            }
534          }
535        }
536      }
537      Parser->freeParsedOperands();
538    }
539  }
540
541  // Set the number of Outputs and Inputs.
542  NumOutputs = Outputs.size();
543  NumInputs = Inputs.size();
544
545  // Set the unique clobbers.
546  for (std::set<std::string>::iterator I = ClobberRegs.begin(),
547         E = ClobberRegs.end(); I != E; ++I)
548    Clobbers.push_back(*I);
549
550  // Merge the various outputs and inputs.  Output are expected first.
551  Names.resize(NumOutputs + NumInputs);
552  Constraints.resize(NumOutputs + NumInputs);
553  Exprs.resize(NumOutputs + NumInputs);
554  for (unsigned i = 0; i < NumOutputs; ++i) {
555    Names[i] = Outputs[i];
556    Constraints[i] = OutputConstraints[i];
557    Exprs[i] = OutputExprs[i];
558  }
559  for (unsigned i = 0, j = NumOutputs; i < NumInputs; ++i, ++j) {
560    Names[j] = Inputs[i];
561    Constraints[j] = InputConstraints[i];
562    Exprs[j] = InputExprs[i];
563  }
564
565  // Build the IR assembly string.
566  std::string AsmStringIR;
567  llvm::raw_string_ostream OS(AsmStringIR);
568  const char *Start = AsmString.c_str();
569  for (SmallVectorImpl<struct AsmOpRewrite>::iterator I = AsmStrRewrites.begin(),
570         E = AsmStrRewrites.end(); I != E; ++I) {
571    const char *Loc = (*I).Loc.getPointer();
572
573    // Emit everything up to the immediate/expression.
574    OS << StringRef(Start, Loc - Start);
575
576    // Rewrite expressions in $N notation.
577    switch ((*I).Kind) {
578    case AOK_Imm:
579      OS << Twine("$$") + StringRef(Loc, (*I).Len);
580      break;
581    case AOK_Input:
582      OS << '$';
583      OS << InputIdx++;
584      break;
585    case AOK_Output:
586      OS << '$';
587      OS << OutputIdx++;
588      break;
589    }
590
591    // Skip the original expression.
592    Start = Loc + (*I).Len;
593  }
594  // Emit the remainder of the asm string.
595  const char *AsmEnd = AsmString.c_str() + AsmString.size();
596  if (Start != AsmEnd)
597    OS << StringRef(Start, AsmEnd - Start);
598
599  AsmString = OS.str();
600  MSAsmStmt *NS =
601    new (Context) MSAsmStmt(Context, AsmLoc, LBraceLoc, /*IsSimple*/ true,
602                            /*IsVolatile*/ true, AsmToks, NumOutputs,
603                            NumInputs, Names, Constraints, Exprs, AsmString,
604                            Clobbers, EndLoc);
605  return Owned(NS);
606}
607