diff --git a/llvm/lib/IR/AsmWriter.cpp b/llvm/lib/IR/AsmWriter.cpp
index 48b3d2bb1bb5..c9748e1387eb 100644
--- a/llvm/lib/IR/AsmWriter.cpp
+++ b/llvm/lib/IR/AsmWriter.cpp
@@ -353,12 +353,11 @@ void llvm::printLLVMNameWithoutPrefix(raw_ostream &OS, StringRef Name) {
   // Scan the name to see if it needs quotes first.
   bool NeedsQuotes = isdigit(static_cast<unsigned char>(Name[0]));
   if (!NeedsQuotes) {
-    for (unsigned i = 0, e = Name.size(); i != e; ++i) {
+    for (unsigned char C : Name) {
       // By making this unsigned, the value passed in to isalnum will always be
       // in the range 0-255.  This is important when building with MSVC because
       // its implementation will assert.  This situation can arise when dealing
       // with UTF-8 multibyte characters.
-      unsigned char C = Name[i];
       if (!isalnum(static_cast<unsigned char>(C)) && C != '-' && C != '.' &&
           C != '_') {
         NeedsQuotes = true;
diff --git a/llvm/lib/MC/MCAsmStreamer.cpp b/llvm/lib/MC/MCAsmStreamer.cpp
index 154b2d051f34..2ca921017171 100644
--- a/llvm/lib/MC/MCAsmStreamer.cpp
+++ b/llvm/lib/MC/MCAsmStreamer.cpp
@@ -1069,16 +1069,14 @@ void MCAsmStreamer::PrintQuotedString(StringRef Data, raw_ostream &OS) const {
   OS << '"';
 
   if (MAI->hasPairedDoubleQuoteStringConstants()) {
-    for (unsigned i = 0, e = Data.size(); i != e; ++i) {
-      unsigned char C = Data[i];
+    for (unsigned char C : Data) {
       if (C == '"')
         OS << "\"\"";
       else
         OS << (char)C;
     }
   } else {
-    for (unsigned i = 0, e = Data.size(); i != e; ++i) {
-      unsigned char C = Data[i];
+    for (unsigned char C : Data) {
       if (C == '"' || C == '\\') {
         OS << '\\' << (char)C;
         continue;
diff --git a/llvm/lib/Option/OptTable.cpp b/llvm/lib/Option/OptTable.cpp
index 37c2fcbab181..19e05b9272bb 100644
--- a/llvm/lib/Option/OptTable.cpp
+++ b/llvm/lib/Option/OptTable.cpp
@@ -150,10 +150,9 @@ OptTable::OptTable(ArrayRef<Info> OptionInfos, bool IgnoreCase)
   for (StringSet<>::const_iterator I = PrefixesUnion.begin(),
                                    E = PrefixesUnion.end(); I != E; ++I) {
     StringRef Prefix = I->getKey();
-    for (StringRef::const_iterator C = Prefix.begin(), CE = Prefix.end();
-                                   C != CE; ++C)
-      if (!is_contained(PrefixChars, *C))
-        PrefixChars.push_back(*C);
+    for (char C : Prefix)
+      if (!is_contained(PrefixChars, C))
+        PrefixChars.push_back(C);
   }
 }
 
diff --git a/llvm/lib/Support/Regex.cpp b/llvm/lib/Support/Regex.cpp
index 0d5cc1c00db1..7a804a1a2297 100644
--- a/llvm/lib/Support/Regex.cpp
+++ b/llvm/lib/Support/Regex.cpp
@@ -218,10 +218,10 @@ bool Regex::isLiteralERE(StringRef Str) {
 
 std::string Regex::escape(StringRef String) {
   std::string RegexStr;
-  for (unsigned i = 0, e = String.size(); i != e; ++i) {
-    if (strchr(RegexMetachars, String[i]))
+  for (char C : String) {
+    if (strchr(RegexMetachars, C))
       RegexStr += '\\';
-    RegexStr += String[i];
+    RegexStr += C;
   }
 
   return RegexStr;
diff --git a/llvm/lib/Support/StringExtras.cpp b/llvm/lib/Support/StringExtras.cpp
index 8abf9f7ce0f1..5683d7005584 100644
--- a/llvm/lib/Support/StringExtras.cpp
+++ b/llvm/lib/Support/StringExtras.cpp
@@ -60,8 +60,7 @@ void llvm::SplitString(StringRef Source,
 }
 
 void llvm::printEscapedString(StringRef Name, raw_ostream &Out) {
-  for (unsigned i = 0, e = Name.size(); i != e; ++i) {
-    unsigned char C = Name[i];
+  for (unsigned char C : Name) {
     if (C == '\\')
       Out << '\\' << C;
     else if (isPrint(C) && C != '"')
diff --git a/llvm/lib/Support/StringRef.cpp b/llvm/lib/Support/StringRef.cpp
index c532a1abe906..652303fdb6a0 100644
--- a/llvm/lib/Support/StringRef.cpp
+++ b/llvm/lib/Support/StringRef.cpp
@@ -227,8 +227,8 @@ size_t StringRef::rfind_insensitive(StringRef Str) const {
 StringRef::size_type StringRef::find_first_of(StringRef Chars,
                                               size_t From) const {
   std::bitset<1 << CHAR_BIT> CharBits;
-  for (size_type i = 0; i != Chars.size(); ++i)
-    CharBits.set((unsigned char)Chars[i]);
+  for (char C : Chars)
+    CharBits.set((unsigned char)C);
 
   for (size_type i = std::min(From, Length), e = Length; i != e; ++i)
     if (CharBits.test((unsigned char)Data[i]))
@@ -252,8 +252,8 @@ StringRef::size_type StringRef::find_first_not_of(char C, size_t From) const {
 StringRef::size_type StringRef::find_first_not_of(StringRef Chars,
                                                   size_t From) const {
   std::bitset<1 << CHAR_BIT> CharBits;
-  for (size_type i = 0; i != Chars.size(); ++i)
-    CharBits.set((unsigned char)Chars[i]);
+  for (char C : Chars)
+    CharBits.set((unsigned char)C);
 
   for (size_type i = std::min(From, Length), e = Length; i != e; ++i)
     if (!CharBits.test((unsigned char)Data[i]))
@@ -268,8 +268,8 @@ StringRef::size_type StringRef::find_first_not_of(StringRef Chars,
 StringRef::size_type StringRef::find_last_of(StringRef Chars,
                                              size_t From) const {
   std::bitset<1 << CHAR_BIT> CharBits;
-  for (size_type i = 0; i != Chars.size(); ++i)
-    CharBits.set((unsigned char)Chars[i]);
+  for (char C : Chars)
+    CharBits.set((unsigned char)C);
 
   for (size_type i = std::min(From, Length) - 1, e = -1; i != e; --i)
     if (CharBits.test((unsigned char)Data[i]))
@@ -293,8 +293,8 @@ StringRef::size_type StringRef::find_last_not_of(char C, size_t From) const {
 StringRef::size_type StringRef::find_last_not_of(StringRef Chars,
                                                  size_t From) const {
   std::bitset<1 << CHAR_BIT> CharBits;
-  for (size_type i = 0, e = Chars.size(); i != e; ++i)
-    CharBits.set((unsigned char)Chars[i]);
+  for (char C : Chars)
+    CharBits.set((unsigned char)C);
 
   for (size_type i = std::min(From, Length) - 1, e = -1; i != e; --i)
     if (!CharBits.test((unsigned char)Data[i]))
diff --git a/llvm/lib/Target/AArch64/MCTargetDesc/AArch64ELFStreamer.cpp b/llvm/lib/Target/AArch64/MCTargetDesc/AArch64ELFStreamer.cpp
index f2a470857d21..78c0e90b1384 100644
--- a/llvm/lib/Target/AArch64/MCTargetDesc/AArch64ELFStreamer.cpp
+++ b/llvm/lib/Target/AArch64/MCTargetDesc/AArch64ELFStreamer.cpp
@@ -177,8 +177,8 @@ public:
     // We can't just use EmitIntValue here, as that will emit a data mapping
     // symbol, and swap the endianness on big-endian systems (instructions are
     // always little-endian).
-    for (unsigned I = 0; I < 4; ++I) {
-      Buffer[I] = uint8_t(Inst);
+    for (char &C : Buffer) {
+      C = uint8_t(Inst);
       Inst >>= 8;
     }
 
diff --git a/llvm/lib/Target/AArch64/MCTargetDesc/AArch64TargetStreamer.cpp b/llvm/lib/Target/AArch64/MCTargetDesc/AArch64TargetStreamer.cpp
index cf1a60643efd..92552c3d41d5 100644
--- a/llvm/lib/Target/AArch64/MCTargetDesc/AArch64TargetStreamer.cpp
+++ b/llvm/lib/Target/AArch64/MCTargetDesc/AArch64TargetStreamer.cpp
@@ -101,8 +101,8 @@ void AArch64TargetStreamer::emitInst(uint32_t Inst) {
   // We can't just use EmitIntValue here, as that will swap the
   // endianness on big-endian systems (instructions are always
   // little-endian).
-  for (unsigned I = 0; I < 4; ++I) {
-    Buffer[I] = uint8_t(Inst);
+  for (char &C : Buffer) {
+    C = uint8_t(Inst);
     Inst >>= 8;
   }
 
diff --git a/llvm/lib/Target/AMDGPU/AMDGPUPrintfRuntimeBinding.cpp b/llvm/lib/Target/AMDGPU/AMDGPUPrintfRuntimeBinding.cpp
index d560d2043f42..7c4eb71882c7 100644
--- a/llvm/lib/Target/AMDGPU/AMDGPUPrintfRuntimeBinding.cpp
+++ b/llvm/lib/Target/AMDGPU/AMDGPUPrintfRuntimeBinding.cpp
@@ -280,10 +280,10 @@ bool AMDGPUPrintfRuntimeBindingImpl::lowerPrintfForGpu(Module &M) {
       }
       LLVM_DEBUG(dbgs() << "Printf format string in source = " << Str.str()
                         << '\n');
-      for (size_t I = 0; I < Str.size(); ++I) {
+      for (char C : Str) {
         // Rest of the C escape sequences (e.g. \') are handled correctly
         // by the MDParser
-        switch (Str[I]) {
+        switch (C) {
         case '\a':
           Sizes << "\\a";
           break;
@@ -308,7 +308,7 @@ bool AMDGPUPrintfRuntimeBindingImpl::lowerPrintfForGpu(Module &M) {
           Sizes << "\\72";
           break;
         default:
-          Sizes << Str[I];
+          Sizes << C;
           break;
         }
       }
diff --git a/llvm/lib/Target/NVPTX/NVPTXAssignValidGlobalNames.cpp b/llvm/lib/Target/NVPTX/NVPTXAssignValidGlobalNames.cpp
index a8a43cee9ab7..34b9dfe87cc2 100644
--- a/llvm/lib/Target/NVPTX/NVPTXAssignValidGlobalNames.cpp
+++ b/llvm/lib/Target/NVPTX/NVPTXAssignValidGlobalNames.cpp
@@ -72,8 +72,7 @@ bool NVPTXAssignValidGlobalNames::runOnModule(Module &M) {
 std::string NVPTXAssignValidGlobalNames::cleanUpName(StringRef Name) {
   std::string ValidName;
   raw_string_ostream ValidNameStream(ValidName);
-  for (unsigned I = 0, E = Name.size(); I != E; ++I) {
-    char C = Name[I];
+  for (char C : Name) {
     if (C == '.' || C == '@') {
       ValidNameStream << "_$_";
     } else {