Index: llvm/lib/Support/CommandLine.cpp
===================================================================
--- llvm/lib/Support/CommandLine.cpp
+++ llvm/lib/Support/CommandLine.cpp
@@ -688,7 +688,9 @@
          O->getNumOccurrencesFlag() == cl::OneOrMore;
 }
 
-static bool isWhitespace(char C) { return strchr(" \t\n\r\f\v", C); }
+static bool isWhitespace(char C) {
+  return C == ' ' || C == '\t' || C == '\r' || C == '\n';
+}
 
 static bool isQuote(char C) { return C == '\"' || C == '\''; }
 
@@ -709,16 +711,19 @@
         break;
     }
 
+    char C = Src[I];
+
     // Backslash escapes the next character.
-    if (I + 1 < E && Src[I] == '\\') {
+    if (I + 1 < E && C == '\\') {
       ++I; // Skip the escape.
       Token.push_back(Src[I]);
       continue;
     }
 
     // Consume a quoted string.
-    if (isQuote(Src[I])) {
-      char Quote = Src[I++];
+    if (isQuote(C)) {
+      char Quote = C;
+      ++I;
       while (I != E && Src[I] != Quote) {
         // Backslash escapes the next character.
         if (Src[I] == '\\' && I + 1 != E)
@@ -732,7 +737,7 @@
     }
 
     // End the token if this is whitespace.
-    if (isWhitespace(Src[I])) {
+    if (isWhitespace(C)) {
       if (!Token.empty())
         NewArgv.push_back(Saver.save(StringRef(Token)).data());
       Token.clear();
@@ -740,7 +745,7 @@
     }
 
     // This is a normal character.  Append it.
-    Token.push_back(Src[I]);
+    Token.push_back(C);
   }
 
   // Append the last token after hitting EOF with no whitespace.
@@ -798,25 +803,27 @@
   // end of the source string.
   enum { INIT, UNQUOTED, QUOTED } State = INIT;
   for (size_t I = 0, E = Src.size(); I != E; ++I) {
+    char C = Src[I];
+
     // INIT state indicates that the current input index is at the start of
     // the string or between tokens.
     if (State == INIT) {
-      if (isWhitespace(Src[I])) {
+      if (isWhitespace(C)) {
         // Mark the end of lines in response files
-        if (MarkEOLs && Src[I] == '\n')
+        if (MarkEOLs && C == '\n')
           NewArgv.push_back(nullptr);
         continue;
       }
-      if (Src[I] == '"') {
+      if (C == '"') {
         State = QUOTED;
         continue;
       }
-      if (Src[I] == '\\') {
+      if (C == '\\') {
         I = parseBackslash(Src, I, Token);
         State = UNQUOTED;
         continue;
       }
-      Token.push_back(Src[I]);
+      Token.push_back(C);
       State = UNQUOTED;
       continue;
     }
@@ -825,38 +832,38 @@
     // quotes.
     if (State == UNQUOTED) {
       // Whitespace means the end of the token.
-      if (isWhitespace(Src[I])) {
+      if (isWhitespace(C)) {
         NewArgv.push_back(Saver.save(StringRef(Token)).data());
         Token.clear();
         State = INIT;
         // Mark the end of lines in response files
-        if (MarkEOLs && Src[I] == '\n')
+        if (MarkEOLs && C == '\n')
           NewArgv.push_back(nullptr);
         continue;
       }
-      if (Src[I] == '"') {
+      if (C == '"') {
         State = QUOTED;
         continue;
       }
-      if (Src[I] == '\\') {
+      if (C == '\\') {
         I = parseBackslash(Src, I, Token);
         continue;
       }
-      Token.push_back(Src[I]);
+      Token.push_back(C);
       continue;
     }
 
     // QUOTED state means that it's reading a token quoted by double quotes.
     if (State == QUOTED) {
-      if (Src[I] == '"') {
+      if (C == '"') {
         State = UNQUOTED;
         continue;
       }
-      if (Src[I] == '\\') {
+      if (C == '\\') {
         I = parseBackslash(Src, I, Token);
         continue;
       }
-      Token.push_back(Src[I]);
+      Token.push_back(C);
     }
   }
   // Append the last token after hitting EOF with no whitespace.