[ADT] Add an in-place version of toHex()

and use that to simplify MD5's hex string code which was previously
using a string stream, as well as Clang's
CGDebugInfo::computeChecksum().

Differential revision: https://reviews.llvm.org/D116960

Author: zmodem

clang/lib/CodeGen/CGDebugInfo.cpp

@@ -354,13 +354,9 @@ CGDebugInfo::computeChecksum(FileID FID, SmallString<32> &Checksum) const {
   if (!MemBuffer)
     return None;
 
-  llvm::MD5 Hash;
-  llvm::MD5::MD5Result Result;
-
-  Hash.update(MemBuffer->getBuffer());
-  Hash.final(Result);
-
-  Hash.stringifyResult(Result, Checksum);
+  llvm::toHex(
+      llvm::MD5::hash(llvm::arrayRefFromStringRef(MemBuffer->getBuffer())),
+      /*LowerCase*/ true, Checksum);
   return llvm::DIFile::CSK_MD5;
 }
 

llvm/include/llvm/ADT/StringExtras.h

@@ -29,7 +29,6 @@
 
 namespace llvm {
 
-template<typename T> class SmallVectorImpl;
 class raw_ostream;
 
 /// hexdigit - Return the hexadecimal character for the
@@ -166,21 +165,26 @@ inline std::string utohexstr(uint64_t X, bool LowerCase = false) {
 
 /// Convert buffer \p Input to its hexadecimal representation.
 /// The returned string is double the size of \p Input.
-inline std::string toHex(StringRef Input, bool LowerCase = false) {
-  size_t Length = Input.size();
-
-  std::string Output;
-  Output.reserve(2 * Length);
-  for (size_t i = 0; i < Length; ++i) {
-    const unsigned char c = Input[i];
-    Output.push_back(hexdigit(c >> 4, LowerCase));
-    Output.push_back(hexdigit(c & 15, LowerCase));
+inline void toHex(ArrayRef<uint8_t> Input, bool LowerCase,
+                  SmallVectorImpl<char> &Output) {
+  const size_t Length = Input.size();
+  Output.resize_for_overwrite(Length * 2);
+
+  for (size_t i = 0; i < Length; i++) {
+    const uint8_t c = Input[i];
+    Output[i * 2    ] = hexdigit(c >> 4, LowerCase);
+    Output[i * 2 + 1] = hexdigit(c & 15, LowerCase);
   }
-  return Output;
 }
 
 inline std::string toHex(ArrayRef<uint8_t> Input, bool LowerCase = false) {
-  return toHex(toStringRef(Input), LowerCase);
+  SmallString<16> Output;
+  toHex(Input, LowerCase, Output);
+  return std::string(Output);
+}
+
+inline std::string toHex(StringRef Input, bool LowerCase = false) {
+  return toHex(arrayRefFromStringRef(Input), LowerCase);
 }
 
 /// Store the binary representation of the two provided values, \p MSB and

llvm/include/llvm/Support/MD5.h

@@ -88,7 +88,7 @@ class MD5 {
 
   /// Translates the bytes in \p Res to a hex string that is
   /// deposited into \p Str. The result will be of length 32.
-  static void stringifyResult(MD5Result &Result, SmallString<32> &Str);
+  static void stringifyResult(MD5Result &Result, SmallVectorImpl<char> &Str);
 
   /// Computes the hash for a given bytes.
   static std::array<uint8_t, 16> hash(ArrayRef<uint8_t> Data);

llvm/lib/Support/MD5.cpp

@@ -40,10 +40,9 @@
 #include "llvm/Support/MD5.h"
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/SmallString.h"
+#include "llvm/ADT/StringExtras.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/Support/Endian.h"
-#include "llvm/Support/Format.h"
-#include "llvm/Support/raw_ostream.h"
 #include <array>
 #include <cstdint>
 #include <cstring>
@@ -281,14 +280,12 @@ StringRef MD5::result() {
 
 SmallString<32> MD5::MD5Result::digest() const {
   SmallString<32> Str;
-  raw_svector_ostream Res(Str);
-  for (int i = 0; i < 16; ++i)
-    Res << format("%.2x", Bytes[i]);
+  toHex(Bytes, /*LowerCase*/ true, Str);
   return Str;
 }
 
-void MD5::stringifyResult(MD5Result &Result, SmallString<32> &Str) {
-  Str = Result.digest();
+void MD5::stringifyResult(MD5Result &Result, SmallVectorImpl<char> &Str) {
+  toHex(Result.Bytes, /*LowerCase*/ true, Str);
 }
 
 std::array<uint8_t, 16> MD5::hash(ArrayRef<uint8_t> Data) {