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   recomputeCurLexerKind();
46 }
47 
48 void Preprocessor::CachingLex(Token &Result) {
49   if (!InCachingLexMode())
50     return;
51 
52   if (CachedLexPos < CachedTokens.size()) {
53     Result = CachedTokens[CachedLexPos++];
54     return;
55   }
56 
57   ExitCachingLexMode();
58   Lex(Result);
59 
60   if (!isBacktrackEnabled()) {
61     // All cached tokens were consumed.
62     CachedTokens.clear();
63     CachedLexPos = 0;
64     return;
65   }
66 
67   // Cache the lexed token.
68   EnterCachingLexMode();
69   CachedTokens.push_back(Result);
70   ++CachedLexPos;
71 }
72 
73 void Preprocessor::EnterCachingLexMode() {
74   if (InCachingLexMode())
75     return;
76 
77   PushIncludeMacroStack();
78   CurLexerKind = CLK_CachingLexer;
79 }
80 
81 
82 const Token &Preprocessor::PeekAhead(unsigned N) {
83   assert(CachedLexPos + N > CachedTokens.size() && "Confused caching.");
84   ExitCachingLexMode();
85   for (unsigned C = CachedLexPos + N - CachedTokens.size(); C > 0; --C) {
86     CachedTokens.push_back(Token());
87     Lex(CachedTokens.back());
88   }
89   EnterCachingLexMode();
90   return CachedTokens.back();
91 }
92 
93 void Preprocessor::AnnotatePreviousCachedTokens(const Token &Tok) {
94   assert(Tok.isAnnotation() && "Expected annotation token");
95   assert(CachedLexPos != 0 && "Expected to have some cached tokens");
96   assert(CachedTokens[CachedLexPos-1].getLastLoc() == Tok.getAnnotationEndLoc()
97          && "The annotation should be until the most recent cached token");
98 
99   // Start from the end of the cached tokens list and look for the token
100   // that is the beginning of the annotation token.
101   for (CachedTokensTy::size_type i = CachedLexPos; i != 0; --i) {
102     CachedTokensTy::iterator AnnotBegin = CachedTokens.begin() + i-1;
103     if (AnnotBegin->getLocation() == Tok.getLocation()) {
104       assert((BacktrackPositions.empty() || BacktrackPositions.back() < i) &&
105              "The backtrack pos points inside the annotated tokens!");
106       // Replace the cached tokens with the single annotation token.
107       if (i < CachedLexPos)
108         CachedTokens.erase(AnnotBegin + 1, CachedTokens.begin() + CachedLexPos);
109       *AnnotBegin = Tok;
110       CachedLexPos = i;
111       return;
112     }
113   }
114 }
115