1 files changed, 163 insertions, 0 deletions
diff --git a/clang/lib/Lex/PPCaching.cpp b/clang/lib/Lex/PPCaching.cpp
new file mode 100644
index 0000000000000..31548d246d5a5
--- /dev/null
+++ b/clang/lib/Lex/PPCaching.cpp
@@ -0,0 +1,163 @@
+//===--- PPCaching.cpp - Handle caching lexed tokens ----------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements pieces of the Preprocessor interface that manage the
+// caching of lexed tokens.
+//
+//===----------------------------------------------------------------------===//
+
+#include "clang/Lex/Preprocessor.h"
+using namespace clang;
+
+// EnableBacktrackAtThisPos - From the point that this method is called, and
+// until CommitBacktrackedTokens() or Backtrack() is called, the Preprocessor
+// keeps track of the lexed tokens so that a subsequent Backtrack() call will
+// make the Preprocessor re-lex the same tokens.
+//
+// Nested backtracks are allowed, meaning that EnableBacktrackAtThisPos can
+// be called multiple times and CommitBacktrackedTokens/Backtrack calls will
+// be combined with the EnableBacktrackAtThisPos calls in reverse order.
+void Preprocessor::EnableBacktrackAtThisPos() {
+  assert(LexLevel == 0 && "cannot use lookahead while lexing");
+  BacktrackPositions.push_back(CachedLexPos);
+  EnterCachingLexMode();
+}
+
+// Disable the last EnableBacktrackAtThisPos call.
+void Preprocessor::CommitBacktrackedTokens() {
+  assert(!BacktrackPositions.empty()
+         && "EnableBacktrackAtThisPos was not called!");
+  BacktrackPositions.pop_back();
+}
+
+// Make Preprocessor re-lex the tokens that were lexed since
+// EnableBacktrackAtThisPos() was previously called.
+void Preprocessor::Backtrack() {
+  assert(!BacktrackPositions.empty()
+         && "EnableBacktrackAtThisPos was not called!");
+  CachedLexPos = BacktrackPositions.back();
+  BacktrackPositions.pop_back();
+  recomputeCurLexerKind();
+}
+
+void Preprocessor::CachingLex(Token &Result) {
+  if (!InCachingLexMode())
+    return;
+
+  // The assert in EnterCachingLexMode should prevent this from happening.
+  assert(LexLevel == 1 &&
+         "should not use token caching within the preprocessor");
+
+  if (CachedLexPos < CachedTokens.size()) {
+    Result = CachedTokens[CachedLexPos++];
+    Result.setFlag(Token::IsReinjected);
+    return;
+  }
+
+  ExitCachingLexMode();
+  Lex(Result);
+
+  if (isBacktrackEnabled()) {
+    // Cache the lexed token.
+    EnterCachingLexModeUnchecked();
+    CachedTokens.push_back(Result);
+    ++CachedLexPos;
+    return;
+  }
+
+  if (CachedLexPos < CachedTokens.size()) {
+    EnterCachingLexModeUnchecked();
+  } else {
+    // All cached tokens were consumed.
+    CachedTokens.clear();
+    CachedLexPos = 0;
+  }
+}
+
+void Preprocessor::EnterCachingLexMode() {
+  // The caching layer sits on top of all the other lexers, so it's incorrect
+  // to cache tokens while inside a nested lex action. The cached tokens would
+  // be retained after returning to the enclosing lex action and, at best,
+  // would appear at the wrong position in the token stream.
+  assert(LexLevel == 0 &&
+         "entered caching lex mode while lexing something else");
+
+  if (InCachingLexMode()) {
+    assert(CurLexerKind == CLK_CachingLexer && "Unexpected lexer kind");
+    return;
+  }
+
+  EnterCachingLexModeUnchecked();
+}
+
+void Preprocessor::EnterCachingLexModeUnchecked() {
+  assert(CurLexerKind != CLK_CachingLexer && "already in caching lex mode");
+  PushIncludeMacroStack();
+  CurLexerKind = CLK_CachingLexer;
+}
+
+
+const Token &Preprocessor::PeekAhead(unsigned N) {
+  assert(CachedLexPos + N > CachedTokens.size() && "Confused caching.");
+  ExitCachingLexMode();
+  for (size_t C = CachedLexPos + N - CachedTokens.size(); C > 0; --C) {
+    CachedTokens.push_back(Token());
+    Lex(CachedTokens.back());
+  }
+  EnterCachingLexMode();
+  return CachedTokens.back();
+}
+
+void Preprocessor::AnnotatePreviousCachedTokens(const Token &Tok) {
+  assert(Tok.isAnnotation() && "Expected annotation token");
+  assert(CachedLexPos != 0 && "Expected to have some cached tokens");
+  assert(CachedTokens[CachedLexPos-1].getLastLoc() == Tok.getAnnotationEndLoc()
+         && "The annotation should be until the most recent cached token");
+
+  // Start from the end of the cached tokens list and look for the token
+  // that is the beginning of the annotation token.
+  for (CachedTokensTy::size_type i = CachedLexPos; i != 0; --i) {
+    CachedTokensTy::iterator AnnotBegin = CachedTokens.begin() + i-1;
+    if (AnnotBegin->getLocation() == Tok.getLocation()) {
+      assert((BacktrackPositions.empty() || BacktrackPositions.back() <= i) &&
+             "The backtrack pos points inside the annotated tokens!");
+      // Replace the cached tokens with the single annotation token.
+      if (i < CachedLexPos)
+        CachedTokens.erase(AnnotBegin + 1, CachedTokens.begin() + CachedLexPos);
+      *AnnotBegin = Tok;
+      CachedLexPos = i;
+      return;
+    }
+  }
+}
+
+bool Preprocessor::IsPreviousCachedToken(const Token &Tok) const {
+  // There's currently no cached token...
+  if (!CachedLexPos)
+    return false;
+
+  const Token LastCachedTok = CachedTokens[CachedLexPos - 1];
+  if (LastCachedTok.getKind() != Tok.getKind())
+    return false;
+
+  int RelOffset = 0;
+  if ((!getSourceManager().isInSameSLocAddrSpace(
+          Tok.getLocation(), getLastCachedTokenLocation(), &RelOffset)) ||
+      RelOffset)
+    return false;
+
+  return true;
+}
+
+void Preprocessor::ReplacePreviousCachedToken(ArrayRef<Token> NewToks) {
+  assert(CachedLexPos != 0 && "Expected to have some cached tokens");
+  CachedTokens.insert(CachedTokens.begin() + CachedLexPos - 1, NewToks.begin(),
+                      NewToks.end());
+  CachedTokens.erase(CachedTokens.begin() + CachedLexPos - 1 + NewToks.size());
+  CachedLexPos += NewToks.size() - 1;
+}