llvm-project

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//===--- PPCaching.cpp - Handle caching lexed tokens ----------------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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//
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// This file implements pieces of the Preprocessor interface that manage the
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// caching of lexed tokens.
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//
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//===----------------------------------------------------------------------===//
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#include "clang/Lex/Preprocessor.h"
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using namespace clang;
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// EnableBacktrackAtThisPos - From the point that this method is called, and
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// until CommitBacktrackedTokens() or Backtrack() is called, the Preprocessor
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// keeps track of the lexed tokens so that a subsequent Backtrack() call will
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// make the Preprocessor re-lex the same tokens.
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//
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// Nested backtracks are allowed, meaning that EnableBacktrackAtThisPos can
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// be called multiple times and CommitBacktrackedTokens/Backtrack calls will
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// be combined with the EnableBacktrackAtThisPos calls in reverse order.
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void Preprocessor::EnableBacktrackAtThisPos() {
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  assert(LexLevel == 0 && "cannot use lookahead while lexing");
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  BacktrackPositions.push_back(CachedLexPos);
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  EnterCachingLexMode();
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}
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// Disable the last EnableBacktrackAtThisPos call.
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void Preprocessor::CommitBacktrackedTokens() {
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  assert(!BacktrackPositions.empty()
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         && "EnableBacktrackAtThisPos was not called!");
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  BacktrackPositions.pop_back();
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}
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// Make Preprocessor re-lex the tokens that were lexed since
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// EnableBacktrackAtThisPos() was previously called.
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void Preprocessor::Backtrack() {
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  assert(!BacktrackPositions.empty()
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         && "EnableBacktrackAtThisPos was not called!");
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  CachedLexPos = BacktrackPositions.back();
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  BacktrackPositions.pop_back();
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  recomputeCurLexerKind();
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}
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void Preprocessor::CachingLex(Token &Result) {
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  if (!InCachingLexMode())
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    return;
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  // The assert in EnterCachingLexMode should prevent this from happening.
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  assert(LexLevel == 1 &&
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         "should not use token caching within the preprocessor");
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  if (CachedLexPos < CachedTokens.size()) {
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    Result = CachedTokens[CachedLexPos++];
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    Result.setFlag(Token::IsReinjected);
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    return;
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  }
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  ExitCachingLexMode();
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  Lex(Result);
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  if (isBacktrackEnabled()) {
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    // Cache the lexed token.
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    EnterCachingLexModeUnchecked();
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    CachedTokens.push_back(Result);
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    ++CachedLexPos;
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    return;
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  }
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  if (CachedLexPos < CachedTokens.size()) {
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    EnterCachingLexModeUnchecked();
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  } else {
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    // All cached tokens were consumed.
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    CachedTokens.clear();
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    CachedLexPos = 0;
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  }
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}
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void Preprocessor::EnterCachingLexMode() {
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  // The caching layer sits on top of all the other lexers, so it's incorrect
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  // to cache tokens while inside a nested lex action. The cached tokens would
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  // be retained after returning to the enclosing lex action and, at best,
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  // would appear at the wrong position in the token stream.
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  assert(LexLevel == 0 &&
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         "entered caching lex mode while lexing something else");
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  if (InCachingLexMode()) {
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    assert(CurLexerCallback == CLK_CachingLexer && "Unexpected lexer kind");
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    return;
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  }
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  EnterCachingLexModeUnchecked();
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}
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void Preprocessor::EnterCachingLexModeUnchecked() {
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  assert(CurLexerCallback != CLK_CachingLexer && "already in caching lex mode");
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  PushIncludeMacroStack();
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  CurLexerCallback = CLK_CachingLexer;
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}
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const Token &Preprocessor::PeekAhead(unsigned N) {
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  assert(CachedLexPos + N > CachedTokens.size() && "Confused caching.");
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  ExitCachingLexMode();
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  for (size_t C = CachedLexPos + N - CachedTokens.size(); C > 0; --C) {
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    CachedTokens.push_back(Token());
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    Lex(CachedTokens.back());
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  }
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  EnterCachingLexMode();
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  return CachedTokens.back();
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}
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void Preprocessor::AnnotatePreviousCachedTokens(const Token &Tok) {
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  assert(Tok.isAnnotation() && "Expected annotation token");
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  assert(CachedLexPos != 0 && "Expected to have some cached tokens");
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  assert(CachedTokens[CachedLexPos-1].getLastLoc() == Tok.getAnnotationEndLoc()
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         && "The annotation should be until the most recent cached token");
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  // Start from the end of the cached tokens list and look for the token
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  // that is the beginning of the annotation token.
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  for (CachedTokensTy::size_type i = CachedLexPos; i != 0; --i) {
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    CachedTokensTy::iterator AnnotBegin = CachedTokens.begin() + i-1;
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    if (AnnotBegin->getLocation() == Tok.getLocation()) {
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      assert((BacktrackPositions.empty() || BacktrackPositions.back() <= i) &&
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             "The backtrack pos points inside the annotated tokens!");
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      // Replace the cached tokens with the single annotation token.
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      if (i < CachedLexPos)
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        CachedTokens.erase(AnnotBegin + 1, CachedTokens.begin() + CachedLexPos);
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      *AnnotBegin = Tok;
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      CachedLexPos = i;
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      return;
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    }
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  }
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}
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bool Preprocessor::IsPreviousCachedToken(const Token &Tok) const {
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  // There's currently no cached token...
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  if (!CachedLexPos)
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    return false;
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  const Token LastCachedTok = CachedTokens[CachedLexPos - 1];
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  if (LastCachedTok.getKind() != Tok.getKind())
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    return false;
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  SourceLocation::IntTy RelOffset = 0;
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  if ((!getSourceManager().isInSameSLocAddrSpace(
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          Tok.getLocation(), getLastCachedTokenLocation(), &RelOffset)) ||
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      RelOffset)
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    return false;
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  return true;
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}
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void Preprocessor::ReplacePreviousCachedToken(ArrayRef<Token> NewToks) {
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  assert(CachedLexPos != 0 && "Expected to have some cached tokens");
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  CachedTokens.insert(CachedTokens.begin() + CachedLexPos - 1, NewToks.begin(),
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                      NewToks.end());
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  CachedTokens.erase(CachedTokens.begin() + CachedLexPos - 1 + NewToks.size());
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  CachedLexPos += NewToks.size() - 1;
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}
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