1 //===- MILexer.cpp - Machine instructions lexer implementation ----------===//
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 the lexing of machine instructions.
11 //
12 //===----------------------------------------------------------------------===//
13 
14 #include "MILexer.h"
15 #include "llvm/ADT/None.h"
16 #include "llvm/ADT/StringExtras.h"
17 #include "llvm/ADT/StringSwitch.h"
18 #include "llvm/ADT/Twine.h"
19 #include <cctype>
20 
21 using namespace llvm;
22 
23 namespace {
24 
25 typedef function_ref<void(StringRef::iterator Loc, const Twine &)>
26     ErrorCallbackType;
27 
28 /// This class provides a way to iterate and get characters from the source
29 /// string.
30 class Cursor {
31   const char *Ptr;
32   const char *End;
33 
34 public:
35   Cursor(NoneType) : Ptr(nullptr), End(nullptr) {}
36 
37   explicit Cursor(StringRef Str) {
38     Ptr = Str.data();
39     End = Ptr + Str.size();
40   }
41 
42   bool isEOF() const { return Ptr == End; }
43 
44   char peek(int I = 0) const { return End - Ptr <= I ? 0 : Ptr[I]; }
45 
46   void advance(unsigned I = 1) { Ptr += I; }
47 
48   StringRef remaining() const { return StringRef(Ptr, End - Ptr); }
49 
50   StringRef upto(Cursor C) const {
51     assert(C.Ptr >= Ptr && C.Ptr <= End);
52     return StringRef(Ptr, C.Ptr - Ptr);
53   }
54 
55   StringRef::iterator location() const { return Ptr; }
56 
57   operator bool() const { return Ptr != nullptr; }
58 };
59 
60 } // end anonymous namespace
61 
62 MIToken &MIToken::reset(TokenKind Kind, StringRef Range) {
63   this->Kind = Kind;
64   this->Range = Range;
65   return *this;
66 }
67 
68 MIToken &MIToken::setStringValue(StringRef StrVal) {
69   StringValue = StrVal;
70   return *this;
71 }
72 
73 MIToken &MIToken::setOwnedStringValue(std::string StrVal) {
74   StringValueStorage = std::move(StrVal);
75   StringValue = StringValueStorage;
76   return *this;
77 }
78 
79 MIToken &MIToken::setIntegerValue(APSInt IntVal) {
80   this->IntVal = std::move(IntVal);
81   return *this;
82 }
83 
84 /// Skip the leading whitespace characters and return the updated cursor.
85 static Cursor skipWhitespace(Cursor C) {
86   while (isblank(C.peek()))
87     C.advance();
88   return C;
89 }
90 
91 static bool isNewlineChar(char C) { return C == '\n' || C == '\r'; }
92 
93 /// Skip a line comment and return the updated cursor.
94 static Cursor skipComment(Cursor C) {
95   if (C.peek() != ';')
96     return C;
97   while (!isNewlineChar(C.peek()) && !C.isEOF())
98     C.advance();
99   return C;
100 }
101 
102 /// Return true if the given character satisfies the following regular
103 /// expression: [-a-zA-Z$._0-9]
104 static bool isIdentifierChar(char C) {
105   return isalpha(C) || isdigit(C) || C == '_' || C == '-' || C == '.' ||
106          C == '$';
107 }
108 
109 /// Unescapes the given string value.
110 ///
111 /// Expects the string value to be quoted.
112 static std::string unescapeQuotedString(StringRef Value) {
113   assert(Value.front() == '"' && Value.back() == '"');
114   Cursor C = Cursor(Value.substr(1, Value.size() - 2));
115 
116   std::string Str;
117   Str.reserve(C.remaining().size());
118   while (!C.isEOF()) {
119     char Char = C.peek();
120     if (Char == '\\') {
121       if (C.peek(1) == '\\') {
122         // Two '\' become one
123         Str += '\\';
124         C.advance(2);
125         continue;
126       }
127       if (isxdigit(C.peek(1)) && isxdigit(C.peek(2))) {
128         Str += hexDigitValue(C.peek(1)) * 16 + hexDigitValue(C.peek(2));
129         C.advance(3);
130         continue;
131       }
132     }
133     Str += Char;
134     C.advance();
135   }
136   return Str;
137 }
138 
139 /// Lex a string constant using the following regular expression: \"[^\"]*\"
140 static Cursor lexStringConstant(Cursor C, ErrorCallbackType ErrorCallback) {
141   assert(C.peek() == '"');
142   for (C.advance(); C.peek() != '"'; C.advance()) {
143     if (C.isEOF() || isNewlineChar(C.peek())) {
144       ErrorCallback(
145           C.location(),
146           "end of machine instruction reached before the closing '\"'");
147       return None;
148     }
149   }
150   C.advance();
151   return C;
152 }
153 
154 static Cursor lexName(Cursor C, MIToken &Token, MIToken::TokenKind Type,
155                       unsigned PrefixLength, ErrorCallbackType ErrorCallback) {
156   auto Range = C;
157   C.advance(PrefixLength);
158   if (C.peek() == '"') {
159     if (Cursor R = lexStringConstant(C, ErrorCallback)) {
160       StringRef String = Range.upto(R);
161       Token.reset(Type, String)
162           .setOwnedStringValue(
163               unescapeQuotedString(String.drop_front(PrefixLength)));
164       return R;
165     }
166     Token.reset(MIToken::Error, Range.remaining());
167     return Range;
168   }
169   while (isIdentifierChar(C.peek()))
170     C.advance();
171   Token.reset(Type, Range.upto(C))
172       .setStringValue(Range.upto(C).drop_front(PrefixLength));
173   return C;
174 }
175 
176 static Cursor maybeLexIntegerOrScalarType(Cursor C, MIToken &Token) {
177   if ((C.peek() != 'i' && C.peek() != 's' && C.peek() != 'p') ||
178       !isdigit(C.peek(1)))
179     return None;
180   char Kind = C.peek();
181   auto Range = C;
182   C.advance(); // Skip 'i', 's', or 'p'
183   while (isdigit(C.peek()))
184     C.advance();
185 
186   Token.reset(Kind == 'i'
187                   ? MIToken::IntegerType
188                   : (Kind == 's' ? MIToken::ScalarType : MIToken::PointerType),
189               Range.upto(C));
190   return C;
191 }
192 
193 static MIToken::TokenKind getIdentifierKind(StringRef Identifier) {
194   return StringSwitch<MIToken::TokenKind>(Identifier)
195       .Case("_", MIToken::underscore)
196       .Case("implicit", MIToken::kw_implicit)
197       .Case("implicit-def", MIToken::kw_implicit_define)
198       .Case("def", MIToken::kw_def)
199       .Case("dead", MIToken::kw_dead)
200       .Case("killed", MIToken::kw_killed)
201       .Case("undef", MIToken::kw_undef)
202       .Case("internal", MIToken::kw_internal)
203       .Case("early-clobber", MIToken::kw_early_clobber)
204       .Case("debug-use", MIToken::kw_debug_use)
205       .Case("tied-def", MIToken::kw_tied_def)
206       .Case("frame-setup", MIToken::kw_frame_setup)
207       .Case("debug-location", MIToken::kw_debug_location)
208       .Case("same_value", MIToken::kw_cfi_same_value)
209       .Case("offset", MIToken::kw_cfi_offset)
210       .Case("def_cfa_register", MIToken::kw_cfi_def_cfa_register)
211       .Case("def_cfa_offset", MIToken::kw_cfi_def_cfa_offset)
212       .Case("def_cfa", MIToken::kw_cfi_def_cfa)
213       .Case("blockaddress", MIToken::kw_blockaddress)
214       .Case("intrinsic", MIToken::kw_intrinsic)
215       .Case("target-index", MIToken::kw_target_index)
216       .Case("half", MIToken::kw_half)
217       .Case("float", MIToken::kw_float)
218       .Case("double", MIToken::kw_double)
219       .Case("x86_fp80", MIToken::kw_x86_fp80)
220       .Case("fp128", MIToken::kw_fp128)
221       .Case("ppc_fp128", MIToken::kw_ppc_fp128)
222       .Case("target-flags", MIToken::kw_target_flags)
223       .Case("volatile", MIToken::kw_volatile)
224       .Case("non-temporal", MIToken::kw_non_temporal)
225       .Case("dereferenceable", MIToken::kw_dereferenceable)
226       .Case("invariant", MIToken::kw_invariant)
227       .Case("align", MIToken::kw_align)
228       .Case("stack", MIToken::kw_stack)
229       .Case("got", MIToken::kw_got)
230       .Case("jump-table", MIToken::kw_jump_table)
231       .Case("constant-pool", MIToken::kw_constant_pool)
232       .Case("call-entry", MIToken::kw_call_entry)
233       .Case("liveout", MIToken::kw_liveout)
234       .Case("address-taken", MIToken::kw_address_taken)
235       .Case("landing-pad", MIToken::kw_landing_pad)
236       .Case("liveins", MIToken::kw_liveins)
237       .Case("successors", MIToken::kw_successors)
238       .Case("floatpred", MIToken::kw_floatpred)
239       .Case("intpred", MIToken::kw_intpred)
240       .Default(MIToken::Identifier);
241 }
242 
243 static Cursor maybeLexIdentifier(Cursor C, MIToken &Token) {
244   if (!isalpha(C.peek()) && C.peek() != '_')
245     return None;
246   auto Range = C;
247   while (isIdentifierChar(C.peek()))
248     C.advance();
249   auto Identifier = Range.upto(C);
250   Token.reset(getIdentifierKind(Identifier), Identifier)
251       .setStringValue(Identifier);
252   return C;
253 }
254 
255 static Cursor maybeLexMachineBasicBlock(Cursor C, MIToken &Token,
256                                         ErrorCallbackType ErrorCallback) {
257   bool IsReference = C.remaining().startswith("%bb.");
258   if (!IsReference && !C.remaining().startswith("bb."))
259     return None;
260   auto Range = C;
261   unsigned PrefixLength = IsReference ? 4 : 3;
262   C.advance(PrefixLength); // Skip '%bb.' or 'bb.'
263   if (!isdigit(C.peek())) {
264     Token.reset(MIToken::Error, C.remaining());
265     ErrorCallback(C.location(), "expected a number after '%bb.'");
266     return C;
267   }
268   auto NumberRange = C;
269   while (isdigit(C.peek()))
270     C.advance();
271   StringRef Number = NumberRange.upto(C);
272   unsigned StringOffset = PrefixLength + Number.size(); // Drop '%bb.<id>'
273   if (C.peek() == '.') {
274     C.advance(); // Skip '.'
275     ++StringOffset;
276     while (isIdentifierChar(C.peek()))
277       C.advance();
278   }
279   Token.reset(IsReference ? MIToken::MachineBasicBlock
280                           : MIToken::MachineBasicBlockLabel,
281               Range.upto(C))
282       .setIntegerValue(APSInt(Number))
283       .setStringValue(Range.upto(C).drop_front(StringOffset));
284   return C;
285 }
286 
287 static Cursor maybeLexIndex(Cursor C, MIToken &Token, StringRef Rule,
288                             MIToken::TokenKind Kind) {
289   if (!C.remaining().startswith(Rule) || !isdigit(C.peek(Rule.size())))
290     return None;
291   auto Range = C;
292   C.advance(Rule.size());
293   auto NumberRange = C;
294   while (isdigit(C.peek()))
295     C.advance();
296   Token.reset(Kind, Range.upto(C)).setIntegerValue(APSInt(NumberRange.upto(C)));
297   return C;
298 }
299 
300 static Cursor maybeLexIndexAndName(Cursor C, MIToken &Token, StringRef Rule,
301                                    MIToken::TokenKind Kind) {
302   if (!C.remaining().startswith(Rule) || !isdigit(C.peek(Rule.size())))
303     return None;
304   auto Range = C;
305   C.advance(Rule.size());
306   auto NumberRange = C;
307   while (isdigit(C.peek()))
308     C.advance();
309   StringRef Number = NumberRange.upto(C);
310   unsigned StringOffset = Rule.size() + Number.size();
311   if (C.peek() == '.') {
312     C.advance();
313     ++StringOffset;
314     while (isIdentifierChar(C.peek()))
315       C.advance();
316   }
317   Token.reset(Kind, Range.upto(C))
318       .setIntegerValue(APSInt(Number))
319       .setStringValue(Range.upto(C).drop_front(StringOffset));
320   return C;
321 }
322 
323 static Cursor maybeLexJumpTableIndex(Cursor C, MIToken &Token) {
324   return maybeLexIndex(C, Token, "%jump-table.", MIToken::JumpTableIndex);
325 }
326 
327 static Cursor maybeLexStackObject(Cursor C, MIToken &Token) {
328   return maybeLexIndexAndName(C, Token, "%stack.", MIToken::StackObject);
329 }
330 
331 static Cursor maybeLexFixedStackObject(Cursor C, MIToken &Token) {
332   return maybeLexIndex(C, Token, "%fixed-stack.", MIToken::FixedStackObject);
333 }
334 
335 static Cursor maybeLexConstantPoolItem(Cursor C, MIToken &Token) {
336   return maybeLexIndex(C, Token, "%const.", MIToken::ConstantPoolItem);
337 }
338 
339 static Cursor maybeLexSubRegisterIndex(Cursor C, MIToken &Token,
340                                        ErrorCallbackType ErrorCallback) {
341   const StringRef Rule = "%subreg.";
342   if (!C.remaining().startswith(Rule))
343     return None;
344   return lexName(C, Token, MIToken::SubRegisterIndex, Rule.size(),
345                  ErrorCallback);
346 }
347 
348 static Cursor maybeLexIRBlock(Cursor C, MIToken &Token,
349                               ErrorCallbackType ErrorCallback) {
350   const StringRef Rule = "%ir-block.";
351   if (!C.remaining().startswith(Rule))
352     return None;
353   if (isdigit(C.peek(Rule.size())))
354     return maybeLexIndex(C, Token, Rule, MIToken::IRBlock);
355   return lexName(C, Token, MIToken::NamedIRBlock, Rule.size(), ErrorCallback);
356 }
357 
358 static Cursor maybeLexIRValue(Cursor C, MIToken &Token,
359                               ErrorCallbackType ErrorCallback) {
360   const StringRef Rule = "%ir.";
361   if (!C.remaining().startswith(Rule))
362     return None;
363   if (isdigit(C.peek(Rule.size())))
364     return maybeLexIndex(C, Token, Rule, MIToken::IRValue);
365   return lexName(C, Token, MIToken::NamedIRValue, Rule.size(), ErrorCallback);
366 }
367 
368 static Cursor lexVirtualRegister(Cursor C, MIToken &Token) {
369   auto Range = C;
370   C.advance(); // Skip '%'
371   auto NumberRange = C;
372   while (isdigit(C.peek()))
373     C.advance();
374   Token.reset(MIToken::VirtualRegister, Range.upto(C))
375       .setIntegerValue(APSInt(NumberRange.upto(C)));
376   return C;
377 }
378 
379 /// Returns true for a character allowed in a register name.
380 static bool isRegisterChar(char C) {
381   return isIdentifierChar(C) && C != '.';
382 }
383 
384 static Cursor maybeLexRegister(Cursor C, MIToken &Token) {
385   if (C.peek() != '%')
386     return None;
387   if (isdigit(C.peek(1)))
388     return lexVirtualRegister(C, Token);
389   auto Range = C;
390   C.advance(); // Skip '%'
391   while (isRegisterChar(C.peek()))
392     C.advance();
393   Token.reset(MIToken::NamedRegister, Range.upto(C))
394       .setStringValue(Range.upto(C).drop_front(1)); // Drop the '%'
395   return C;
396 }
397 
398 static Cursor maybeLexGlobalValue(Cursor C, MIToken &Token,
399                                   ErrorCallbackType ErrorCallback) {
400   if (C.peek() != '@')
401     return None;
402   if (!isdigit(C.peek(1)))
403     return lexName(C, Token, MIToken::NamedGlobalValue, /*PrefixLength=*/1,
404                    ErrorCallback);
405   auto Range = C;
406   C.advance(1); // Skip the '@'
407   auto NumberRange = C;
408   while (isdigit(C.peek()))
409     C.advance();
410   Token.reset(MIToken::GlobalValue, Range.upto(C))
411       .setIntegerValue(APSInt(NumberRange.upto(C)));
412   return C;
413 }
414 
415 static Cursor maybeLexExternalSymbol(Cursor C, MIToken &Token,
416                                      ErrorCallbackType ErrorCallback) {
417   if (C.peek() != '$')
418     return None;
419   return lexName(C, Token, MIToken::ExternalSymbol, /*PrefixLength=*/1,
420                  ErrorCallback);
421 }
422 
423 static bool isValidHexFloatingPointPrefix(char C) {
424   return C == 'H' || C == 'K' || C == 'L' || C == 'M';
425 }
426 
427 static Cursor lexFloatingPointLiteral(Cursor Range, Cursor C, MIToken &Token) {
428   C.advance();
429   // Skip over [0-9]*([eE][-+]?[0-9]+)?
430   while (isdigit(C.peek()))
431     C.advance();
432   if ((C.peek() == 'e' || C.peek() == 'E') &&
433       (isdigit(C.peek(1)) ||
434        ((C.peek(1) == '-' || C.peek(1) == '+') && isdigit(C.peek(2))))) {
435     C.advance(2);
436     while (isdigit(C.peek()))
437       C.advance();
438   }
439   Token.reset(MIToken::FloatingPointLiteral, Range.upto(C));
440   return C;
441 }
442 
443 static Cursor maybeLexHexadecimalLiteral(Cursor C, MIToken &Token) {
444   if (C.peek() != '0' || (C.peek(1) != 'x' && C.peek(1) != 'X'))
445     return None;
446   Cursor Range = C;
447   C.advance(2);
448   unsigned PrefLen = 2;
449   if (isValidHexFloatingPointPrefix(C.peek())) {
450     C.advance();
451     PrefLen++;
452   }
453   while (isxdigit(C.peek()))
454     C.advance();
455   StringRef StrVal = Range.upto(C);
456   if (StrVal.size() <= PrefLen)
457     return None;
458   if (PrefLen == 2)
459     Token.reset(MIToken::HexLiteral, Range.upto(C));
460   else // It must be 3, which means that there was a floating-point prefix.
461     Token.reset(MIToken::FloatingPointLiteral, Range.upto(C));
462   return C;
463 }
464 
465 static Cursor maybeLexNumericalLiteral(Cursor C, MIToken &Token) {
466   if (!isdigit(C.peek()) && (C.peek() != '-' || !isdigit(C.peek(1))))
467     return None;
468   auto Range = C;
469   C.advance();
470   while (isdigit(C.peek()))
471     C.advance();
472   if (C.peek() == '.')
473     return lexFloatingPointLiteral(Range, C, Token);
474   StringRef StrVal = Range.upto(C);
475   Token.reset(MIToken::IntegerLiteral, StrVal).setIntegerValue(APSInt(StrVal));
476   return C;
477 }
478 
479 static MIToken::TokenKind getMetadataKeywordKind(StringRef Identifier) {
480   return StringSwitch<MIToken::TokenKind>(Identifier)
481       .Case("!tbaa", MIToken::md_tbaa)
482       .Case("!alias.scope", MIToken::md_alias_scope)
483       .Case("!noalias", MIToken::md_noalias)
484       .Case("!range", MIToken::md_range)
485       .Default(MIToken::Error);
486 }
487 
488 static Cursor maybeLexExlaim(Cursor C, MIToken &Token,
489                              ErrorCallbackType ErrorCallback) {
490   if (C.peek() != '!')
491     return None;
492   auto Range = C;
493   C.advance(1);
494   if (isdigit(C.peek()) || !isIdentifierChar(C.peek())) {
495     Token.reset(MIToken::exclaim, Range.upto(C));
496     return C;
497   }
498   while (isIdentifierChar(C.peek()))
499     C.advance();
500   StringRef StrVal = Range.upto(C);
501   Token.reset(getMetadataKeywordKind(StrVal), StrVal);
502   if (Token.isError())
503     ErrorCallback(Token.location(),
504                   "use of unknown metadata keyword '" + StrVal + "'");
505   return C;
506 }
507 
508 static MIToken::TokenKind symbolToken(char C) {
509   switch (C) {
510   case ',':
511     return MIToken::comma;
512   case '.':
513     return MIToken::dot;
514   case '=':
515     return MIToken::equal;
516   case ':':
517     return MIToken::colon;
518   case '(':
519     return MIToken::lparen;
520   case ')':
521     return MIToken::rparen;
522   case '{':
523     return MIToken::lbrace;
524   case '}':
525     return MIToken::rbrace;
526   case '+':
527     return MIToken::plus;
528   case '-':
529     return MIToken::minus;
530   case '<':
531     return MIToken::less;
532   case '>':
533     return MIToken::greater;
534   default:
535     return MIToken::Error;
536   }
537 }
538 
539 static Cursor maybeLexSymbol(Cursor C, MIToken &Token) {
540   MIToken::TokenKind Kind;
541   unsigned Length = 1;
542   if (C.peek() == ':' && C.peek(1) == ':') {
543     Kind = MIToken::coloncolon;
544     Length = 2;
545   } else
546     Kind = symbolToken(C.peek());
547   if (Kind == MIToken::Error)
548     return None;
549   auto Range = C;
550   C.advance(Length);
551   Token.reset(Kind, Range.upto(C));
552   return C;
553 }
554 
555 static Cursor maybeLexNewline(Cursor C, MIToken &Token) {
556   if (!isNewlineChar(C.peek()))
557     return None;
558   auto Range = C;
559   C.advance();
560   Token.reset(MIToken::Newline, Range.upto(C));
561   return C;
562 }
563 
564 static Cursor maybeLexEscapedIRValue(Cursor C, MIToken &Token,
565                                      ErrorCallbackType ErrorCallback) {
566   if (C.peek() != '`')
567     return None;
568   auto Range = C;
569   C.advance();
570   auto StrRange = C;
571   while (C.peek() != '`') {
572     if (C.isEOF() || isNewlineChar(C.peek())) {
573       ErrorCallback(
574           C.location(),
575           "end of machine instruction reached before the closing '`'");
576       Token.reset(MIToken::Error, Range.remaining());
577       return C;
578     }
579     C.advance();
580   }
581   StringRef Value = StrRange.upto(C);
582   C.advance();
583   Token.reset(MIToken::QuotedIRValue, Range.upto(C)).setStringValue(Value);
584   return C;
585 }
586 
587 StringRef llvm::lexMIToken(StringRef Source, MIToken &Token,
588                            ErrorCallbackType ErrorCallback) {
589   auto C = skipComment(skipWhitespace(Cursor(Source)));
590   if (C.isEOF()) {
591     Token.reset(MIToken::Eof, C.remaining());
592     return C.remaining();
593   }
594 
595   if (Cursor R = maybeLexIntegerOrScalarType(C, Token))
596     return R.remaining();
597   if (Cursor R = maybeLexMachineBasicBlock(C, Token, ErrorCallback))
598     return R.remaining();
599   if (Cursor R = maybeLexIdentifier(C, Token))
600     return R.remaining();
601   if (Cursor R = maybeLexJumpTableIndex(C, Token))
602     return R.remaining();
603   if (Cursor R = maybeLexStackObject(C, Token))
604     return R.remaining();
605   if (Cursor R = maybeLexFixedStackObject(C, Token))
606     return R.remaining();
607   if (Cursor R = maybeLexConstantPoolItem(C, Token))
608     return R.remaining();
609   if (Cursor R = maybeLexSubRegisterIndex(C, Token, ErrorCallback))
610     return R.remaining();
611   if (Cursor R = maybeLexIRBlock(C, Token, ErrorCallback))
612     return R.remaining();
613   if (Cursor R = maybeLexIRValue(C, Token, ErrorCallback))
614     return R.remaining();
615   if (Cursor R = maybeLexRegister(C, Token))
616     return R.remaining();
617   if (Cursor R = maybeLexGlobalValue(C, Token, ErrorCallback))
618     return R.remaining();
619   if (Cursor R = maybeLexExternalSymbol(C, Token, ErrorCallback))
620     return R.remaining();
621   if (Cursor R = maybeLexHexadecimalLiteral(C, Token))
622     return R.remaining();
623   if (Cursor R = maybeLexNumericalLiteral(C, Token))
624     return R.remaining();
625   if (Cursor R = maybeLexExlaim(C, Token, ErrorCallback))
626     return R.remaining();
627   if (Cursor R = maybeLexSymbol(C, Token))
628     return R.remaining();
629   if (Cursor R = maybeLexNewline(C, Token))
630     return R.remaining();
631   if (Cursor R = maybeLexEscapedIRValue(C, Token, ErrorCallback))
632     return R.remaining();
633 
634   Token.reset(MIToken::Error, C.remaining());
635   ErrorCallback(C.location(),
636                 Twine("unexpected character '") + Twine(C.peek()) + "'");
637   return C.remaining();
638 }
639