lib/Lex/PPCaching.cpp

   1 //===--- PPCaching.cpp - Handle caching lexed tokens ----------------------===//
   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 pieces of the Preprocessor interface that manage the
  11 // caching of lexed tokens.
  12 //
  13 //===----------------------------------------------------------------------===//
  14
  15 #include "clang/Lex/Preprocessor.h"
  16 using namespace clang;
  17
  18 /// EnableBacktrackAtThisPos - From the point that this method is called, and
  19 /// until CommitBacktrackedTokens() or Backtrack() is called, the Preprocessor
  20 /// keeps track of the lexed tokens so that a subsequent Backtrack() call will
  21 /// make the Preprocessor re-lex the same tokens.
  22 ///
  23 /// Nested backtracks are allowed, meaning that EnableBacktrackAtThisPos can
  24 /// be called multiple times and CommitBacktrackedTokens/Backtrack calls will
  25 /// be combined with the EnableBacktrackAtThisPos calls in reverse order.
  26 void Preprocessor::EnableBacktrackAtThisPos() {
  27   BacktrackPositions.push_back(CachedLexPos);
  28   EnterCachingLexMode();
  29 }
  30
  31 /// CommitBacktrackedTokens - Disable the last EnableBacktrackAtThisPos call.
  32 void Preprocessor::CommitBacktrackedTokens() {
  33   assert(!BacktrackPositions.empty()
  34          && "EnableBacktrackAtThisPos was not called!");
  35   BacktrackPositions.pop_back();
  36 }
  37
  38 /// Backtrack - Make Preprocessor re-lex the tokens that were lexed since
  39 /// EnableBacktrackAtThisPos() was previously called.
  40 void Preprocessor::Backtrack() {
  41   assert(!BacktrackPositions.empty()
  42          && "EnableBacktrackAtThisPos was not called!");
  43   CachedLexPos = BacktrackPositions.back();
  44   BacktrackPositions.pop_back();
  45 }
  46
  47 void Preprocessor::CachingLex(Token &Result) {
  48   if (!InCachingLexMode())
  49     return;
  50
  51   if (CachedLexPos < CachedTokens.size()) {
  52     Result = CachedTokens[CachedLexPos++];
  53     return;
  54   }
  55
  56   ExitCachingLexMode();
  57   Lex(Result);
  58
  59   if (!isBacktrackEnabled()) {
  60     // All cached tokens were consumed.
  61     CachedTokens.clear();
  62     CachedLexPos = 0;
  63     return;
  64   }
  65
  66   // Cache the lexed token.
  67   EnterCachingLexMode();
  68   CachedTokens.push_back(Result);
  69   ++CachedLexPos;
  70 }
  71
  72 void Preprocessor::EnterCachingLexMode() {
  73   if (InCachingLexMode())
  74     return;
  75
  76   PushIncludeMacroStack();
  77 }
  78
  79
  80 const Token &Preprocessor::PeekAhead(unsigned N) {
  81   assert(CachedLexPos + N > CachedTokens.size() && "Confused caching.");
  82   ExitCachingLexMode();
  83   for (unsigned C = CachedLexPos + N - CachedTokens.size(); C > 0; --C) {
  84     CachedTokens.push_back(Token());
  85     Lex(CachedTokens.back());
  86   }
  87   EnterCachingLexMode();
  88   return CachedTokens.back();
  89 }
  90
  91 void Preprocessor::AnnotatePreviousCachedTokens(const Token &Tok) {
  92   assert(Tok.isAnnotation() && "Expected annotation token");
  93   assert(CachedLexPos != 0 && "Expected to have some cached tokens");
  94   assert(CachedTokens[CachedLexPos-1].getLastLoc() == Tok.getAnnotationEndLoc()
  95          && "The annotation should be until the most recent cached token");
  96
  97   // Start from the end of the cached tokens list and look for the token
  98   // that is the beginning of the annotation token.
  99   for (CachedTokensTy::size_type i = CachedLexPos; i != 0; --i) {
 100     CachedTokensTy::iterator AnnotBegin = CachedTokens.begin() + i-1;
 101     if (AnnotBegin->getLocation() == Tok.getLocation()) {
 102       assert((BacktrackPositions.empty() || BacktrackPositions.back() < i) &&
 103              "The backtrack pos points inside the annotated tokens!");
 104       // Replace the cached tokens with the single annotation token.
 105       if (i < CachedLexPos)
 106         CachedTokens.erase(AnnotBegin + 1, CachedTokens.begin() + CachedLexPos);
 107       *AnnotBegin = Tok;
 108       CachedLexPos = i;
 109       return;
 110     }
 111   }
 112 }