Index: libc/src/string/aarch64/memcmp.cpp
===================================================================
--- libc/src/string/aarch64/memcmp.cpp
+++ libc/src/string/aarch64/memcmp.cpp
@@ -14,20 +14,21 @@
 namespace __llvm_libc {
 namespace aarch64 {
 
-static int memcmp_impl(const char *lhs, const char *rhs, size_t count) {
+static int memcmp_impl(const char *lhs, const char *rhs,
+                       size_t count) noexcept {
   if (count == 0)
     return 0;
   if (count == 1)
     return ThreeWayCompare<_1>(lhs, rhs);
-  else if (count == 2)
+  if (count == 2)
     return ThreeWayCompare<_2>(lhs, rhs);
-  else if (count == 3)
+  if (count == 3)
     return ThreeWayCompare<_3>(lhs, rhs);
-  else if (count < 8)
+  if (count < 8)
     return ThreeWayCompare<HeadTail<_4>>(lhs, rhs, count);
-  else if (count < 16)
+  if (count < 16)
     return ThreeWayCompare<HeadTail<_8>>(lhs, rhs, count);
-  else if (count < 128) {
+  if (count < 128) {
     if (Equals<_16>(lhs, rhs)) {
       if (count < 32)
         return ThreeWayCompare<Tail<_16>>(lhs, rhs, count);
@@ -49,11 +50,11 @@
 } // namespace aarch64
 
 LLVM_LIBC_FUNCTION(int, memcmp,
-                   (const void *lhs, const void *rhs, size_t count)) {
+                   (const void *lhs, const void *rhs, size_t count))
+noexcept {
 
-  const char *_lhs = reinterpret_cast<const char *>(lhs);
-  const char *_rhs = reinterpret_cast<const char *>(rhs);
-  return aarch64::memcmp_impl(_lhs, _rhs, count);
+  return aarch64::memcmp_impl(reinterpret_cast<const char *>(lhs),
+                              reinterpret_cast<const char *>(rhs), count);
 }
 
 } // namespace __llvm_libc
Index: libc/src/string/aarch64/memcpy.cpp
===================================================================
--- libc/src/string/aarch64/memcpy.cpp
+++ libc/src/string/aarch64/memcpy.cpp
@@ -42,7 +42,7 @@
 //   with little change on the code side.
 // This implementation has been tuned for Neoverse-N1.
 static void memcpy_aarch64(char *__restrict dst, const char *__restrict src,
-                           size_t count) {
+                           size_t count) noexcept {
   if (count == 0)
     return;
   if (count == 1)
@@ -68,7 +68,8 @@
 
 LLVM_LIBC_FUNCTION(void *, memcpy,
                    (void *__restrict dst, const void *__restrict src,
-                    size_t size)) {
+                    size_t size))
+noexcept {
   memcpy_aarch64(reinterpret_cast<char *>(dst),
                  reinterpret_cast<const char *>(src), size);
   return dst;
Index: libc/src/string/memchr.cpp
===================================================================
--- libc/src/string/memchr.cpp
+++ libc/src/string/memchr.cpp
@@ -15,9 +15,10 @@
 namespace __llvm_libc {
 
 // TODO: Look at performance benefits of comparing words.
-LLVM_LIBC_FUNCTION(void *, memchr, (const void *src, int c, size_t n)) {
+LLVM_LIBC_FUNCTION(void *, memchr, (const void *src, int c, size_t n)) noexcept{
   return internal::find_first_character(
-      reinterpret_cast<const unsigned char *>(src), c, n);
+      reinterpret_cast<const unsigned char *>(src),
+      static_cast<unsigned char>(c), n);
 }
 
 } // namespace __llvm_libc
Index: libc/src/string/memcmp.cpp
===================================================================
--- libc/src/string/memcmp.cpp
+++ libc/src/string/memcmp.cpp
@@ -14,7 +14,7 @@
 
 // TODO: It is a simple implementation, an optimized version is preparing.
 LLVM_LIBC_FUNCTION(int, memcmp,
-                   (const void *lhs, const void *rhs, size_t count)) {
+                   (const void *lhs, const void *rhs, size_t count)) noexcept {
   const unsigned char *_lhs = reinterpret_cast<const unsigned char *>(lhs);
   const unsigned char *_rhs = reinterpret_cast<const unsigned char *>(rhs);
   for (size_t i = 0; i < count; ++i)
Index: libc/src/string/memcpy.cpp
===================================================================
--- libc/src/string/memcpy.cpp
+++ libc/src/string/memcpy.cpp
@@ -31,7 +31,7 @@
 // - As compilers and processors get better, the generated code is improved
 //   with little change on the code side.
 static void memcpy_impl(char *__restrict dst, const char *__restrict src,
-                        size_t count) {
+                        size_t count) noexcept {
   // Use scalar strategies (_1, _2, _3 ...)
   using namespace __llvm_libc::scalar;
 
@@ -60,7 +60,7 @@
 
 LLVM_LIBC_FUNCTION(void *, memcpy,
                    (void *__restrict dst, const void *__restrict src,
-                    size_t size)) {
+                    size_t size)) noexcept {
   memcpy_impl(reinterpret_cast<char *>(dst),
               reinterpret_cast<const char *>(src), size);
   return dst;
Index: libc/src/string/memmove.cpp
===================================================================
--- libc/src/string/memmove.cpp
+++ libc/src/string/memmove.cpp
@@ -15,22 +15,25 @@
 
 namespace __llvm_libc {
 
-static inline void move_byte_forward(char *dest_m, const char *src_m,
-                                     size_t count) {
-  for (size_t offset = 0; count; --count, ++offset)
+static inline void move_byte_forward(unsigned char *dest_m,
+                                     const unsigned char *src_m, size_t count) noexcept {
+  for (size_t offset = 0; offset != count; ++offset)
     dest_m[offset] = src_m[offset];
 }
 
-static inline void move_byte_backward(char *dest_m, const char *src_m,
-                                      size_t count) {
-  for (size_t offset = count - 1; count; --count, --offset)
-    dest_m[offset] = src_m[offset];
+static inline void move_byte_backward(unsigned char *dest_m,
+                                      const unsigned char *src_m,
+                                      size_t count) noexcept {
+  if (count != 0) { // Avoid underflow
+    for (size_t offset = count - 1; offset != 0; --offset)
+      dest_m[offset] = src_m[offset];
+  }
 }
 
 LLVM_LIBC_FUNCTION(void *, memmove,
-                   (void *dest, const void *src, size_t count)) {
-  char *dest_c = reinterpret_cast<char *>(dest);
-  const char *src_c = reinterpret_cast<const char *>(src);
+                   (void *dest, const void *src, size_t count)) noexcept {
+  unsigned char *dest_c = reinterpret_cast<unsigned char *>(dest);
+  const unsigned char *src_c = reinterpret_cast<const unsigned char *>(src);
 
   // If the distance between src_c and dest_c is equal to or greater
   // than count (integerAbs(src_c - dest_c) >= count), they would not overlap.
@@ -58,7 +61,7 @@
   // TODO: Optimize `move_byte_xxx(...)` functions.
   if (dest_c < src_c)
     move_byte_forward(dest_c, src_c, count);
-  if (dest_c > src_c)
+  else if (dest_c > src_c)
     move_byte_backward(dest_c, src_c, count);
   return dest;
 }
Index: libc/src/string/memory_utils/elements.h
===================================================================
--- libc/src/string/memory_utils/elements.h
+++ libc/src/string/memory_utils/elements.h
@@ -26,44 +26,46 @@
 
 // Fixed-size copies from 'src' to 'dst'.
 template <typename Element>
-void Copy(char *__restrict dst, const char *__restrict src) {
+void Copy(char *__restrict dst, const char *__restrict src) noexcept {
   Element::Copy(dst, src);
 }
 // Runtime-size copies from 'src' to 'dst'.
 template <typename Element>
-void Copy(char *__restrict dst, const char *__restrict src, size_t size) {
+void Copy(char *__restrict dst, const char *__restrict src,
+          size_t size) noexcept {
   Element::Copy(dst, src, size);
 }
 
 // Fixed-size equality between 'lhs' and 'rhs'.
-template <typename Element> bool Equals(const char *lhs, const char *rhs) {
+template <typename Element>
+bool Equals(const char *lhs, const char *rhs) noexcept {
   return Element::Equals(lhs, rhs);
 }
 // Runtime-size equality between 'lhs' and 'rhs'.
 template <typename Element>
-bool Equals(const char *lhs, const char *rhs, size_t size) {
+bool Equals(const char *lhs, const char *rhs, size_t size) noexcept {
   return Element::Equals(lhs, rhs, size);
 }
 
 // Fixed-size three-way comparison between 'lhs' and 'rhs'.
 template <typename Element>
-int ThreeWayCompare(const char *lhs, const char *rhs) {
+int ThreeWayCompare(const char *lhs, const char *rhs) noexcept {
   return Element::ThreeWayCompare(lhs, rhs);
 }
 // Runtime-size three-way comparison between 'lhs' and 'rhs'.
 template <typename Element>
-int ThreeWayCompare(const char *lhs, const char *rhs, size_t size) {
+int ThreeWayCompare(const char *lhs, const char *rhs, size_t size) noexcept {
   return Element::ThreeWayCompare(lhs, rhs, size);
 }
 
 // Fixed-size initialization.
 template <typename Element>
-void SplatSet(char *dst, const unsigned char value) {
+void SplatSet(char *dst, const unsigned char value) noexcept {
   Element::SplatSet(dst, value);
 }
 // Runtime-size initialization.
 template <typename Element>
-void SplatSet(char *dst, const unsigned char value, size_t size) {
+void SplatSet(char *dst, const unsigned char value, size_t size) noexcept {
   Element::SplatSet(dst, value, size);
 }
 
@@ -76,14 +78,14 @@
 template <typename Element, size_t ElementCount> struct Repeated {
   static constexpr size_t kSize = ElementCount * Element::kSize;
 
-  static void Copy(char *__restrict dst, const char *__restrict src) {
+  static void Copy(char *__restrict dst, const char *__restrict src) noexcept {
     for (size_t i = 0; i < ElementCount; ++i) {
       const size_t offset = i * Element::kSize;
       Element::Copy(dst + offset, src + offset);
     }
   }
 
-  static bool Equals(const char *lhs, const char *rhs) {
+  static bool Equals(const char *lhs, const char *rhs) noexcept {
     for (size_t i = 0; i < ElementCount; ++i) {
       const size_t offset = i * Element::kSize;
       if (!Element::Equals(lhs + offset, rhs + offset))
@@ -92,18 +94,17 @@
     return true;
   }
 
-  static int ThreeWayCompare(const char *lhs, const char *rhs) {
+  static int ThreeWayCompare(const char *lhs, const char *rhs) noexcept {
     for (size_t i = 0; i < ElementCount; ++i) {
       const size_t offset = i * Element::kSize;
       // We make the assumption that 'Equals' si cheaper than 'ThreeWayCompare'.
-      if (Element::Equals(lhs + offset, rhs + offset))
-        continue;
-      return Element::ThreeWayCompare(lhs + offset, rhs + offset);
+      if (!Element::Equals(lhs + offset, rhs + offset))
+        return Element::ThreeWayCompare(lhs + offset, rhs + offset);
     }
     return 0;
   }
 
-  static void SplatSet(char *dst, const unsigned char value) {
+  static void SplatSet(char *dst, const unsigned char value) noexcept {
     for (size_t i = 0; i < ElementCount; ++i) {
       const size_t offset = i * Element::kSize;
       Element::SplatSet(dst + offset, value);
@@ -119,25 +120,25 @@
 template <typename Head, typename... Tail> struct Chained<Head, Tail...> {
   static constexpr size_t kSize = Head::kSize + Chained<Tail...>::kSize;
 
-  static void Copy(char *__restrict dst, const char *__restrict src) {
+  static void Copy(char *__restrict dst, const char *__restrict src) noexcept {
     Chained<Tail...>::Copy(dst + Head::kSize, src + Head::kSize);
     __llvm_libc::Copy<Head>(dst, src);
   }
 
-  static bool Equals(const char *lhs, const char *rhs) {
+  static bool Equals(const char *lhs, const char *rhs) noexcept {
     if (!__llvm_libc::Equals<Head>(lhs, rhs))
       return false;
     return Chained<Tail...>::Equals(lhs + Head::kSize, rhs + Head::kSize);
   }
 
-  static int ThreeWayCompare(const char *lhs, const char *rhs) {
-    if (__llvm_libc::Equals<Head>(lhs, rhs))
-      return Chained<Tail...>::ThreeWayCompare(lhs + Head::kSize,
-                                               rhs + Head::kSize);
-    return __llvm_libc::ThreeWayCompare<Head>(lhs, rhs);
+  static int ThreeWayCompare(const char *lhs, const char *rhs) noexcept {
+    if (!__llvm_libc::Equals<Head>(lhs, rhs))
+      return __llvm_libc::ThreeWayCompare<Head>(lhs, rhs);
+    return Chained<Tail...>::ThreeWayCompare(lhs + Head::kSize,
+                                             rhs + Head::kSize);
   }
 
-  static void SplatSet(char *dst, const unsigned char value) {
+  static void SplatSet(char *dst, const unsigned char value) noexcept {
     Chained<Tail...>::SplatSet(dst + Head::kSize, value);
     __llvm_libc::SplatSet<Head>(dst, value);
   }
@@ -168,23 +169,25 @@
 // Precondition: `size >= T::kSize`.
 template <typename T> struct Tail {
   static void Copy(char *__restrict dst, const char *__restrict src,
-                   size_t size) {
+                   size_t size) noexcept {
     return T::Copy(dst + offset(size), src + offset(size));
   }
 
-  static bool Equals(const char *lhs, const char *rhs, size_t size) {
+  static bool Equals(const char *lhs, const char *rhs, size_t size) noexcept {
     return T::Equals(lhs + offset(size), rhs + offset(size));
   }
 
-  static int ThreeWayCompare(const char *lhs, const char *rhs, size_t size) {
+  static int ThreeWayCompare(const char *lhs, const char *rhs,
+                             size_t size) noexcept {
     return T::ThreeWayCompare(lhs + offset(size), rhs + offset(size));
   }
 
-  static void SplatSet(char *dst, const unsigned char value, size_t size) {
+  static void SplatSet(char *dst, const unsigned char value,
+                       size_t size) noexcept {
     return T::SplatSet(dst + offset(size), value);
   }
 
-  static size_t offset(size_t size) { return size - T::kSize; }
+  static size_t offset(size_t size) noexcept { return size - T::kSize; }
 };
 
 // Perform the operation on the first and last 'T::kSize' bytes of the buffer.
@@ -199,24 +202,26 @@
 // Precondition: `size >= T::kSize && size <= 2 x T::kSize`.
 template <typename T> struct HeadTail {
   static void Copy(char *__restrict dst, const char *__restrict src,
-                   size_t size) {
+                   size_t size) noexcept {
     T::Copy(dst, src);
     Tail<T>::Copy(dst, src, size);
   }
 
-  static bool Equals(const char *lhs, const char *rhs, size_t size) {
+  static bool Equals(const char *lhs, const char *rhs, size_t size) noexcept {
     if (!T::Equals(lhs, rhs))
       return false;
     return Tail<T>::Equals(lhs, rhs, size);
   }
 
-  static int ThreeWayCompare(const char *lhs, const char *rhs, size_t size) {
+  static int ThreeWayCompare(const char *lhs, const char *rhs,
+                             size_t size) noexcept {
     if (!T::Equals(lhs, rhs))
       return T::ThreeWayCompare(lhs, rhs);
     return Tail<T>::ThreeWayCompare(lhs, rhs, size);
   }
 
-  static void SplatSet(char *dst, const unsigned char value, size_t size) {
+  static void SplatSet(char *dst, const unsigned char value,
+                       size_t size) noexcept {
     T::SplatSet(dst, value);
     Tail<T>::SplatSet(dst, value, size);
   }
@@ -356,7 +361,7 @@
 template <size_t Size> struct Builtin {
   static constexpr size_t kSize = Size;
 
-  static void Copy(char *__restrict dst, const char *__restrict src) {
+  static void Copy(char *__restrict dst, const char *__restrict src) noexcept {
 #if LLVM_LIBC_HAVE_MEMORY_SANITIZER || LLVM_LIBC_HAVE_ADDRESS_SANITIZER
     ForLoopCopy(dst, src);
 #elif __has_builtin(__builtin_memcpy_inline)
@@ -376,15 +381,15 @@
 #define LLVM_LIBC_MEMCMP __builtin_memcmp
 #endif
 
-  static bool Equals(const char *lhs, const char *rhs) {
+  static bool Equals(const char *lhs, const char *rhs) noexcept {
     return LLVM_LIBC_MEMCMP(lhs, rhs, kSize) == 0;
   }
 
-  static int ThreeWayCompare(const char *lhs, const char *rhs) {
+  static int ThreeWayCompare(const char *lhs, const char *rhs) noexcept {
     return LLVM_LIBC_MEMCMP(lhs, rhs, kSize);
   }
 
-  static void SplatSet(char *dst, const unsigned char value) {
+  static void SplatSet(char *dst, const unsigned char value) noexcept {
     __builtin_memset(dst, value, kSize);
   }
 
@@ -392,7 +397,8 @@
   // Copies `kSize` bytes from `src` to `dst` using a for loop.
   // This code requires the use of `-fno-buitin-memcpy` to prevent the compiler
   // from turning the for-loop back into `__builtin_memcpy`.
-  static void ForLoopCopy(char *__restrict dst, const char *__restrict src) {
+  static void ForLoopCopy(char *__restrict dst,
+                          const char *__restrict src) noexcept {
     for (size_t i = 0; i < kSize; ++i)
       dst[i] = src[i];
   }
@@ -418,58 +424,62 @@
 template <typename T> struct Scalar {
   static constexpr size_t kSize = sizeof(T);
 
-  static void Copy(char *__restrict dst, const char *__restrict src) {
+  static void Copy(char *__restrict dst, const char *__restrict src) noexcept {
     Store(dst, Load(src));
   }
 
-  static bool Equals(const char *lhs, const char *rhs) {
+  static bool Equals(const char *lhs, const char *rhs) noexcept {
     return Load(lhs) == Load(rhs);
   }
 
-  static int ThreeWayCompare(const char *lhs, const char *rhs) {
+  static int ThreeWayCompare(const char *lhs, const char *rhs) noexcept {
     return ScalarThreeWayCompare(Load(lhs), Load(rhs));
   }
 
-  static void SplatSet(char *dst, const unsigned char value) {
+  static void SplatSet(char *dst, const unsigned char value) noexcept {
     Store(dst, GetSplattedValue(value));
   }
 
   static int ScalarThreeWayCompare(T a, T b);
 
 private:
-  static T Load(const char *ptr) {
+  static T Load(const char *ptr) noexcept {
     T value;
     builtin::Builtin<kSize>::Copy(reinterpret_cast<char *>(&value), ptr);
     return value;
   }
-  static void Store(char *ptr, T value) {
+  static void Store(char *ptr, T value) noexcept {
     builtin::Builtin<kSize>::Copy(ptr, reinterpret_cast<const char *>(&value));
   }
-  static T GetSplattedValue(const unsigned char value) {
+  static T GetSplattedValue(const unsigned char value) noexcept {
     return T(~0) / T(0xFF) * T(value);
   }
 };
 
 template <>
-inline int Scalar<uint8_t>::ScalarThreeWayCompare(uint8_t a, uint8_t b) {
+inline int Scalar<uint8_t>::ScalarThreeWayCompare(uint8_t a,
+                                                  uint8_t b) noexcept {
   const int16_t la = Endian::ToBigEndian(a);
   const int16_t lb = Endian::ToBigEndian(b);
   return la - lb;
 }
 template <>
-inline int Scalar<uint16_t>::ScalarThreeWayCompare(uint16_t a, uint16_t b) {
+inline int Scalar<uint16_t>::ScalarThreeWayCompare(uint16_t a,
+                                                   uint16_t b) noexcept {
   const int32_t la = Endian::ToBigEndian(a);
   const int32_t lb = Endian::ToBigEndian(b);
   return la - lb;
 }
 template <>
-inline int Scalar<uint32_t>::ScalarThreeWayCompare(uint32_t a, uint32_t b) {
+inline int Scalar<uint32_t>::ScalarThreeWayCompare(uint32_t a,
+                                                   uint32_t b) noexcept {
   const uint32_t la = Endian::ToBigEndian(a);
   const uint32_t lb = Endian::ToBigEndian(b);
   return la > lb ? 1 : la < lb ? -1 : 0;
 }
 template <>
-inline int Scalar<uint64_t>::ScalarThreeWayCompare(uint64_t a, uint64_t b) {
+inline int Scalar<uint64_t>::ScalarThreeWayCompare(uint64_t a,
+                                                   uint64_t b) noexcept {
   const uint64_t la = Endian::ToBigEndian(a);
   const uint64_t lb = Endian::ToBigEndian(b);
   return la > lb ? 1 : la < lb ? -1 : 0;
Index: libc/src/string/memory_utils/memset_utils.h
===================================================================
--- libc/src/string/memory_utils/memset_utils.h
+++ libc/src/string/memory_utils/memset_utils.h
@@ -48,7 +48,7 @@
 // may waste up to 31 Bytes. Benchmarks showed that SetAlignedBlocks<64> was not
 // superior for sizes that mattered.
 inline static void GeneralPurposeMemset(char *dst, unsigned char value,
-                                        size_t count) {
+                                        size_t count) noexcept {
 #if defined(__i386__) || defined(__x86_64__)
   using namespace ::__llvm_libc::x86;
 #else
Index: libc/src/string/memory_utils/utils.h
===================================================================
--- libc/src/string/memory_utils/utils.h
+++ libc/src/string/memory_utils/utils.h
@@ -72,11 +72,11 @@
 }
 
 // Returns the offset from `ptr` to the next cache line.
-static inline intptr_t offset_to_next_cache_line(const void *ptr) {
+static inline intptr_t offset_to_next_cache_line(const void *ptr) noexcept {
   return offset_to_next_aligned<LLVM_LIBC_CACHELINE_SIZE>(ptr);
 }
 
-template <size_t alignment, typename T> static T *assume_aligned(T *ptr) {
+template <size_t alignment, typename T> static T *assume_aligned(T *ptr) noexcept {
   return reinterpret_cast<T *>(__builtin_assume_aligned(ptr, alignment));
 }
 
Index: libc/src/string/memrchr.cpp
===================================================================
--- libc/src/string/memrchr.cpp
+++ libc/src/string/memrchr.cpp
@@ -12,13 +12,13 @@
 
 namespace __llvm_libc {
 
-LLVM_LIBC_FUNCTION(void *, memrchr, (const void *src, int c, size_t n)) {
+LLVM_LIBC_FUNCTION(void *, memrchr, (const void *src, int c, size_t n))
+noexcept {
   const unsigned char *str = reinterpret_cast<const unsigned char *>(src);
-  const unsigned char ch = c;
+  const unsigned char ch = static_cast<unsigned char>(c);
   for (; n != 0; --n) {
-    const unsigned char *s = str + n - 1;
-    if (*s == ch)
-      return const_cast<unsigned char *>(s);
+    if (*(--str) == ch)
+      return const_cast<unsigned char *>(str);
   }
   return nullptr;
 }
Index: libc/src/string/strcat.cpp
===================================================================
--- libc/src/string/strcat.cpp
+++ libc/src/string/strcat.cpp
@@ -15,7 +15,7 @@
 namespace __llvm_libc {
 
 LLVM_LIBC_FUNCTION(char *, strcat,
-                   (char *__restrict dest, const char *__restrict src)) {
+                   (char *__restrict dest, const char *__restrict src)) noexcept {
   __llvm_libc::strcpy(dest + internal::string_length(dest), src);
   return dest;
 }
Index: libc/src/string/strchr.cpp
===================================================================
--- libc/src/string/strchr.cpp
+++ libc/src/string/strchr.cpp
@@ -13,13 +13,13 @@
 namespace __llvm_libc {
 
 // TODO: Look at performance benefits of comparing words.
-LLVM_LIBC_FUNCTION(char *, strchr, (const char *src, int c)) {
-  unsigned char *str =
-      const_cast<unsigned char *>(reinterpret_cast<const unsigned char *>(src));
-  const unsigned char ch = c;
-  for (; *str && *str != ch; ++str)
-    ;
-  return *str == ch ? reinterpret_cast<char *>(str) : nullptr;
+LLVM_LIBC_FUNCTION(char *, strchr, (const char *src, int c)) noexcept {
+  const char ch = static_cast<char>(c);
+  for (; *src != ch; ++src)
+    if (*src == '\0')
+      return nullptr;
+
+  return const_cast<char *>(src);
 }
 
 } // namespace __llvm_libc
Index: libc/src/string/strcmp.cpp
===================================================================
--- libc/src/string/strcmp.cpp
+++ libc/src/string/strcmp.cpp
@@ -13,7 +13,7 @@
 namespace __llvm_libc {
 
 // TODO: Look at benefits for comparing words at a time.
-LLVM_LIBC_FUNCTION(int, strcmp, (const char *left, const char *right)) {
+LLVM_LIBC_FUNCTION(int, strcmp, (const char *left, const char *right)) noexcept {
   for (; *left && *left == *right; ++left, ++right)
     ;
   return *reinterpret_cast<const unsigned char *>(left) -
Index: libc/src/string/strcpy.cpp
===================================================================
--- libc/src/string/strcpy.cpp
+++ libc/src/string/strcpy.cpp
@@ -15,7 +15,8 @@
 namespace __llvm_libc {
 
 LLVM_LIBC_FUNCTION(char *, strcpy,
-                   (char *__restrict dest, const char *__restrict src)) {
+                   (char *__restrict dest, const char *__restrict src))
+noexcept {
   return reinterpret_cast<char *>(
       __llvm_libc::memcpy(dest, src, internal::string_length(src) + 1));
 }
Index: libc/src/string/strcspn.cpp
===================================================================
--- libc/src/string/strcspn.cpp
+++ libc/src/string/strcspn.cpp
@@ -13,7 +13,8 @@
 
 namespace __llvm_libc {
 
-LLVM_LIBC_FUNCTION(size_t, strcspn, (const char *src, const char *segment)) {
+LLVM_LIBC_FUNCTION(size_t, strcspn, (const char *src, const char *segment))
+noexcept {
   return internal::complementary_span(src, segment);
 }
 
Index: libc/src/string/string_utils.h
===================================================================
--- libc/src/string/string_utils.h
+++ libc/src/string/string_utils.h
@@ -17,31 +17,33 @@
 
 // Returns the length of a string, denoted by the first occurrence
 // of a null terminator.
-static inline size_t string_length(const char *src) {
-  size_t length;
-  for (length = 0; *src; ++src, ++length)
+static inline size_t string_length(const char *src) noexcept {
+  const char *const initial = src;
+  for (; *src != '\0'; ++src)
     ;
-  return length;
+  return src - initial;
 }
 
 // Returns the first occurrence of 'ch' within the first 'n' characters of
 // 'src'. If 'ch' is not found, returns nullptr.
 static inline void *find_first_character(const unsigned char *src,
-                                         unsigned char ch, size_t n) {
-  for (; n && *src != ch; --n, ++src)
-    ;
-  return n ? const_cast<unsigned char *>(src) : nullptr;
+                                         unsigned char ch, size_t n) noexcept {
+  for (; n != 0; --n, ++src)
+    if (*src == ch)
+      return const_cast<unsigned char *>(src);
+  return nullptr;
 }
 
 // Returns the maximum length span that contains only characters not found in
 // 'segment'. If no characters are found, returns the length of 'src'.
-static inline size_t complementary_span(const char *src, const char *segment) {
-  const char *initial = src;
+static inline size_t complementary_span(const char *src,
+                                        const char *segment) noexcept {
+  const char *const initial = src;
   cpp::Bitset<256> bitset;
 
-  for (; *segment; ++segment)
+  for (; *segment != '\0'; ++segment)
     bitset.set(*segment);
-  for (; *src && !bitset.test(*src); ++src)
+  for (; *src != '\0' && !bitset.test(*src); ++src)
     ;
   return src - initial;
 }
@@ -57,24 +59,23 @@
 // terminating character is reached, returns a nullptr.
 static inline char *string_token(char *__restrict src,
                                  const char *__restrict delimiter_string,
-                                 char **__restrict saveptr) {
+                                 char **__restrict saveptr) noexcept {
   cpp::Bitset<256> delimiter_set;
-  for (; *delimiter_string; ++delimiter_string)
+  for (; *delimiter_string != '\0'; ++delimiter_string)
     delimiter_set.set(*delimiter_string);
 
   src = src ? src : *saveptr;
-  for (; *src && delimiter_set.test(*src); ++src)
+  for (; *src != '\0' && delimiter_set.test(*src); ++src)
     ;
-  if (!*src) {
+  if (*src == '\0') {
     *saveptr = src;
     return nullptr;
   }
   char *token = src;
-  for (; *src && !delimiter_set.test(*src); ++src)
+  for (; *src != '\0' && !delimiter_set.test(*src); ++src)
     ;
-  if (*src) {
-    *src = '\0';
-    ++src;
+  if (*src != '\0') {
+    *src++ = '\0';
   }
   *saveptr = src;
   return token;
Index: libc/src/string/strlen.cpp
===================================================================
--- libc/src/string/strlen.cpp
+++ libc/src/string/strlen.cpp
@@ -15,7 +15,7 @@
 
 // TODO: investigate the performance of this function.
 // There might be potential for compiler optimization.
-LLVM_LIBC_FUNCTION(size_t, strlen, (const char *src)) {
+LLVM_LIBC_FUNCTION(size_t, strlen, (const char *src)) noexcept {
   return internal::string_length(src);
 }
 
Index: libc/src/string/strncpy.cpp
===================================================================
--- libc/src/string/strncpy.cpp
+++ libc/src/string/strncpy.cpp
@@ -15,7 +15,8 @@
 
 LLVM_LIBC_FUNCTION(char *, strncpy,
                    (char *__restrict dest, const char *__restrict src,
-                    size_t n)) {
+                    size_t n))
+noexcept {
   size_t i = 0;
   // Copy up until \0 is found.
   for (; i < n && src[i] != '\0'; ++i)
Index: libc/src/string/strnlen.cpp
===================================================================
--- libc/src/string/strnlen.cpp
+++ libc/src/string/strnlen.cpp
@@ -14,7 +14,7 @@
 
 namespace __llvm_libc {
 
-LLVM_LIBC_FUNCTION(size_t, strnlen, (const char *src, size_t n)) {
+LLVM_LIBC_FUNCTION(size_t, strnlen, (const char *src, size_t n)) noexcept {
   const void *temp = internal::find_first_character(
       reinterpret_cast<const unsigned char *>(src), '\0', n);
   return temp ? reinterpret_cast<const char *>(temp) - src : n;
Index: libc/src/string/strpbrk.cpp
===================================================================
--- libc/src/string/strpbrk.cpp
+++ libc/src/string/strpbrk.cpp
@@ -13,7 +13,8 @@
 
 namespace __llvm_libc {
 
-LLVM_LIBC_FUNCTION(char *, strpbrk, (const char *src, const char *breakset)) {
+LLVM_LIBC_FUNCTION(char *, strpbrk, (const char *src, const char *breakset))
+noexcept {
   src += internal::complementary_span(src, breakset);
   return *src ? const_cast<char *>(src) : nullptr;
 }
Index: libc/src/string/strrchr.cpp
===================================================================
--- libc/src/string/strrchr.cpp
+++ libc/src/string/strrchr.cpp
@@ -12,13 +12,13 @@
 
 namespace __llvm_libc {
 
-LLVM_LIBC_FUNCTION(char *, strrchr, (const char *src, int c)) {
-  const char ch = c;
+LLVM_LIBC_FUNCTION(char *, strrchr, (const char *src, int c)) noexcept {
+  const char ch = static_cast<char>(c);
   char *last_occurrence = nullptr;
   do {
     if (*src == ch)
       last_occurrence = const_cast<char *>(src);
-  } while (*src++);
+  } while (*src++ != '\0');
   return last_occurrence;
 }
 
Index: libc/src/string/strspn.cpp
===================================================================
--- libc/src/string/strspn.cpp
+++ libc/src/string/strspn.cpp
@@ -14,7 +14,8 @@
 
 namespace __llvm_libc {
 
-LLVM_LIBC_FUNCTION(size_t, strspn, (const char *src, const char *segment)) {
+LLVM_LIBC_FUNCTION(size_t, strspn, (const char *src, const char *segment))
+noexcept {
   const char *initial = src;
   cpp::Bitset<256> bitset;
 
Index: libc/src/string/strstr.cpp
===================================================================
--- libc/src/string/strstr.cpp
+++ libc/src/string/strstr.cpp
@@ -15,7 +15,8 @@
 
 // TODO: This is a simple brute force implementation. This can be
 // improved upon using well known string matching algorithms.
-LLVM_LIBC_FUNCTION(char *, strstr, (const char *haystack, const char *needle)) {
+LLVM_LIBC_FUNCTION(char *, strstr, (const char *haystack, const char *needle))
+noexcept {
   for (size_t i = 0; haystack[i]; ++i) {
     size_t j;
     for (j = 0; haystack[i + j] && haystack[i + j] == needle[j]; ++j)
Index: libc/src/string/strtok.cpp
===================================================================
--- libc/src/string/strtok.cpp
+++ libc/src/string/strtok.cpp
@@ -17,7 +17,8 @@
 
 LLVM_LIBC_FUNCTION(char *, strtok,
                    (char *__restrict src,
-                    const char *__restrict delimiter_string)) {
+                    const char *__restrict delimiter_string))
+noexcept {
   return internal::string_token(src, delimiter_string, &strtok_str);
 }
 
Index: libc/src/string/strtok_r.cpp
===================================================================
--- libc/src/string/strtok_r.cpp
+++ libc/src/string/strtok_r.cpp
@@ -16,7 +16,8 @@
 LLVM_LIBC_FUNCTION(char *, strtok_r,
                    (char *__restrict src,
                     const char *__restrict delimiter_string,
-                    char **__restrict saveptr)) {
+                    char **__restrict saveptr))
+noexcept {
   return internal::string_token(src, delimiter_string, saveptr);
 }
 
Index: libc/src/string/x86_64/memcpy.cpp
===================================================================
--- libc/src/string/x86_64/memcpy.cpp
+++ libc/src/string/x86_64/memcpy.cpp
@@ -63,7 +63,7 @@
 // - As compilers and processors get better, the generated code is improved
 //   with little change on the code side.
 static void memcpy_x86(char *__restrict dst, const char *__restrict src,
-                       size_t count) {
+                       size_t count) noexcept {
   // Use x86 strategies (_1, _2, _3 ...)
   using namespace __llvm_libc::x86;