Index: lib/Lex/PPCaching.cpp
===================================================================
--- lib/Lex/PPCaching.cpp
+++ lib/Lex/PPCaching.cpp
@@ -86,7 +86,7 @@
 const Token &Preprocessor::PeekAhead(unsigned N) {
   assert(CachedLexPos + N > CachedTokens.size() && "Confused caching.");
   ExitCachingLexMode();
-  for (unsigned C = CachedLexPos + N - CachedTokens.size(); C > 0; --C) {
+  for (size_t C = CachedLexPos + N - CachedTokens.size(); C > 0; --C) {
     CachedTokens.push_back(Token());
     Lex(CachedTokens.back());
   }
Index: lib/Lex/PPLexerChange.cpp
===================================================================
--- lib/Lex/PPLexerChange.cpp
+++ lib/Lex/PPLexerChange.cpp
@@ -40,10 +40,10 @@
   // If there are any stacked lexers, we're in a #include.
   assert(IsFileLexer(IncludeMacroStack[0]) &&
          "Top level include stack isn't our primary lexer?");
-  for (unsigned i = 1, e = IncludeMacroStack.size(); i != e; ++i)
-    if (IsFileLexer(IncludeMacroStack[i]))
-      return false;
-  return true;
+  return std::none_of(IncludeMacroStack.begin() + 1, IncludeMacroStack.end(),
+                      [](const IncludeStackInfo &ISI) -> bool {
+    return IsFileLexer(ISI);
+  });
 }
 
 /// getCurrentLexer - Return the current file lexer being lexed from.  Note
@@ -54,8 +54,7 @@
     return CurPPLexer;
 
   // Look for a stacked lexer.
-  for (unsigned i = IncludeMacroStack.size(); i != 0; --i) {
-    const IncludeStackInfo& ISI = IncludeMacroStack[i-1];
+  for (const IncludeStackInfo &ISI : llvm::reverse(IncludeMacroStack)) {
     if (IsFileLexer(ISI))
       return ISI.ThePPLexer;
   }
@@ -571,8 +570,7 @@
   // explicit EOD token.
   PreprocessorLexer *FoundLexer = nullptr;
   bool LexerWasInPPMode = false;
-  for (unsigned i = 0, e = IncludeMacroStack.size(); i != e; ++i) {
-    IncludeStackInfo &ISI = *(IncludeMacroStack.end()-i-1);
+  for (const IncludeStackInfo &ISI : llvm::reverse(IncludeMacroStack)) {
     if (ISI.ThePPLexer == nullptr) continue;  // Scan for a real lexer.
 
     // Once we find a real lexer, mark it as raw mode (disabling macro
Index: lib/Lex/PPMacroExpansion.cpp
===================================================================
--- lib/Lex/PPMacroExpansion.cpp
+++ lib/Lex/PPMacroExpansion.cpp
@@ -411,8 +411,7 @@
     // macro stack.
     if (CurPPLexer)
       return false;
-    for (unsigned i = IncludeMacroStack.size(); i != 0; --i) {
-      IncludeStackInfo &Entry = IncludeMacroStack[i-1];
+    for (const IncludeStackInfo &Entry : llvm::reverse(IncludeMacroStack)) {
       if (Entry.TheLexer)
         Val = Entry.TheLexer->isNextPPTokenLParen();
       else if (Entry.ThePTHLexer)
@@ -501,9 +500,7 @@
     } else {
       Callbacks->MacroExpands(Identifier, M, ExpansionRange, Args);
       if (!DelayedMacroExpandsCallbacks.empty()) {
-        for (unsigned i = 0, e = DelayedMacroExpandsCallbacks.size(); i != e;
-             ++i) {
-          MacroExpandsInfo &Info = DelayedMacroExpandsCallbacks[i];
+        for (const MacroExpandsInfo &Info : DelayedMacroExpandsCallbacks) {
           // FIXME: We lose macro args info with delayed callback.
           Callbacks->MacroExpands(Info.Tok, Info.MD, Info.Range,
                                   /*Args=*/nullptr);
@@ -757,7 +754,7 @@
     assert(Tok.isOneOf(tok::l_paren, tok::comma) &&
            "only expect argument separators here");
 
-    unsigned ArgTokenStart = ArgTokens.size();
+    size_t ArgTokenStart = ArgTokens.size();
     SourceLocation ArgStartLoc = Tok.getLocation();
 
     // C99 6.10.3p11: Keep track of the number of l_parens we have seen.  Note
@@ -1009,10 +1006,10 @@
   if (cacheNeedsToGrow) {
     // Go through all the TokenLexers whose 'Tokens' pointer points in the
     // buffer and update the pointers to the (potential) new buffer array.
-    for (unsigned i = 0, e = MacroExpandingLexersStack.size(); i != e; ++i) {
+    for (const auto &Lexer : MacroExpandingLexersStack) {
       TokenLexer *prevLexer;
       size_t tokIndex;
-      std::tie(prevLexer, tokIndex) = MacroExpandingLexersStack[i];
+      std::tie(prevLexer, tokIndex) = Lexer;
       prevLexer->Tokens = MacroExpandedTokens.data() + tokIndex;
     }
   }
Index: lib/Lex/Pragma.cpp
===================================================================
--- lib/Lex/Pragma.cpp
+++ lib/Lex/Pragma.cpp
@@ -281,7 +281,7 @@
 
     // Remove escaped quotes and escapes.
     unsigned ResultPos = 1;
-    for (unsigned i = 1, e = StrVal.size() - 1; i != e; ++i) {
+    for (size_t i = 1, e = StrVal.size() - 1; i != e; ++i) {
       // Skip escapes.  \\ -> '\' and \" -> '"'.
       if (StrVal[i] == '\\' && i + 1 < e &&
           (StrVal[i + 1] == '\\' || StrVal[i + 1] == '"'))
Index: lib/Lex/TokenConcatenation.cpp
===================================================================
--- lib/Lex/TokenConcatenation.cpp
+++ lib/Lex/TokenConcatenation.cpp
@@ -232,7 +232,7 @@
     // it as an identifier.
     if (!PrevTok.hasUDSuffix())
       return false;
-    // FALL THROUGH.
+    LLVM_FALLTHROUGH;
   case tok::identifier:   // id+id or id+number or id+L"foo".
     // id+'.'... will not append.
     if (Tok.is(tok::numeric_constant))
Index: lib/Lex/TokenLexer.cpp
===================================================================
--- lib/Lex/TokenLexer.cpp
+++ lib/Lex/TokenLexer.cpp
@@ -275,7 +275,7 @@
 
       // If the arg token expanded into anything, append it.
       if (ResultArgToks->isNot(tok::eof)) {
-        unsigned FirstResult = ResultToks.size();
+        size_t FirstResult = ResultToks.size();
         unsigned NumToks = MacroArgs::getArgLength(ResultArgToks);
         ResultToks.append(ResultArgToks, ResultArgToks+NumToks);
 
@@ -289,8 +289,8 @@
 
         // If the '##' came from expanding an argument, turn it into 'unknown'
         // to avoid pasting.
-        for (unsigned i = FirstResult, e = ResultToks.size(); i != e; ++i) {
-          Token &Tok = ResultToks[i];
+        for (Token &Tok : llvm::make_range(ResultToks.begin() + FirstResult,
+                                           ResultToks.end())) {
           if (Tok.is(tok::hashhash))
             Tok.setKind(tok::unknown);
         }
@@ -333,9 +333,8 @@
 
       // If the '##' came from expanding an argument, turn it into 'unknown'
       // to avoid pasting.
-      for (unsigned i = ResultToks.size() - NumToks, e = ResultToks.size();
-             i != e; ++i) {
-        Token &Tok = ResultToks[i];
+      for (Token &Tok : llvm::make_range(ResultToks.end() - NumToks,
+                                         ResultToks.end())) {
         if (Tok.is(tok::hashhash))
           Tok.setKind(tok::unknown);
       }