[demangler][NFC] Utility header cleanups

[urnathan]

Summary

A few items I came across ...

a) Using a do...while loop in the number formatter means we do not have to special case zero.

b) Let's use 'if (auto size = ...) {}' for appending to the output buffer.

c) We should also be using memcpy there, not memmove -- the string being appended is never part of the current buffer.

d) Let's put all the operator<< functions together.

e) I find 'if (cond) frob(..., true) ; elseOD frob(..., false)' somewhat confusing. Let's just use std::abs in the signed integer printer and let CSE decide about the duplicate < 0 testing.

f) Let's have as many as possible return *this. That's both more consistent, and allows tailcalls in some cases (the actual number formatter has a local array though).

These changes removed around 100 bytes from the demangler's instructions on x86_64.

[ChuanqiXu]

LGTM.

[serge-sans-paille]

Thanks o/

libcxxabi/src/demangle/Utility.h

if (N + CurrentPosition >= BufferCapacity) {
       if (BufferCapacity < N + CurrentPosition)
         BufferCapacity = N + CurrentPosition;
       Buffer = static_cast<char *>(std::realloc(Buffer, BufferCapacity));
       if (Buffer == nullptr)
         std::terminate();
     }
   }
 
-  void writeUnsigned(uint64_t N, bool isNeg = false) {
-    // Handle special case...
-    if (N == 0) {
-      *this << '0';
-      return;
-    }
-
+  OutputBuffer &writeUnsigned(uint64_t N, bool isNeg = false) {
     std::array<char, 21> Temp;
     char *TempPtr = Temp.data() + Temp.size();
 
-    while (N) {
+    // Output at least one character.
+    do {
       *--TempPtr = char('0' + N % 10);
       N /= 10;
-    }
+    } while (N);
 
-    // Add negative sign...
+    // Add negative sign.
     if (isNeg)
       *--TempPtr = '-';
-    this->operator<<(StringView(TempPtr, Temp.data() + Temp.size()));
+
+    return operator+=(StringView(TempPtr, Temp.data() + Temp.size()));
   }
 
 public:
   OutputBuffer(char *StartBuf, size_t Size)
       : Buffer(StartBuf), CurrentPosition(0), BufferCapacity(Size) {}
   OutputBuffer() = default;
   void reset(char *Buffer_, size_t BufferCapacity_) {
     CurrentPosition = 0;
     Buffer = Buffer_;
     BufferCapacity = BufferCapacity_;
   }
 
   /// If a ParameterPackExpansion (or similar type) is encountered, the offset
   /// into the pack that we're currently printing.
   unsigned CurrentPackIndex = std::numeric_limits<unsigned>::max();
   unsigned CurrentPackMax = std::numeric_limits<unsigned>::max();
 
   OutputBuffer &operator+=(StringView R) {
-    size_t Size = R.size();
-    if (Size == 0)
-      return *this;
+    if (size_t Size = R.size()) {
       grow(Size);
-    std::memmove(Buffer + CurrentPosition, R.begin(), Size);
+      std::memcpy(Buffer + CurrentPosition, R.begin(), Size);
       CurrentPosition += Size;
+    }
     return *this;
   }
 
   OutputBuffer &operator+=(char C) {
     grow(1);
     Buffer[CurrentPosition++] = C;
     return *this;
   }
 
-  OutputBuffer &operator<<(StringView R) { return (*this += R); }
-
   OutputBuffer prepend(StringView R) {
     size_t Size = R.size();
 
     grow(Size);
     std::memmove(Buffer + Size, Buffer, CurrentPosition);
     std::memcpy(Buffer, R.begin(), Size);
     CurrentPosition += Size;
 
     return *this;
   }
 
+  OutputBuffer &operator<<(StringView R) { return (*this += R); }
+
   OutputBuffer &operator<<(char C) { return (*this += C); }
 
   OutputBuffer &operator<<(long long N) {
-    if (N < 0)
-      writeUnsigned(static_cast<unsigned long long>(-N), true);
-    else
-      writeUnsigned(static_cast<unsigned long long>(N));
-    return *this;
+    return writeUnsigned(static_cast<unsigned long long>(std::abs(N)), N < 0);
   }
 
   OutputBuffer &operator<<(unsigned long long N) {
-    writeUnsigned(N, false);
-    return *this;
+    return writeUnsigned(N, false);
   }
 
   OutputBuffer &operator<<(long N) {
     return this->operator<<(static_cast<long long>(N));
   }
 
   OutputBuffer &operator<<(unsigned long N) {
     return this->operator<<(static_cast<unsigned long long>(N));

llvm/include/llvm/Demangle/Utility.h

if (N + CurrentPosition >= BufferCapacity) {
       if (BufferCapacity < N + CurrentPosition)
         BufferCapacity = N + CurrentPosition;
       Buffer = static_cast<char *>(std::realloc(Buffer, BufferCapacity));
       if (Buffer == nullptr)
         std::terminate();
     }
   }
 
-  void writeUnsigned(uint64_t N, bool isNeg = false) {
-    // Handle special case...
-    if (N == 0) {
-      *this << '0';
-      return;
-    }
-
+  OutputBuffer &writeUnsigned(uint64_t N, bool isNeg = false) {
     std::array<char, 21> Temp;
     char *TempPtr = Temp.data() + Temp.size();
 
-    while (N) {
+    // Output at least one character.
+    do {
       *--TempPtr = char('0' + N % 10);
       N /= 10;
-    }
+    } while (N);
 
-    // Add negative sign...
+    // Add negative sign.
     if (isNeg)
       *--TempPtr = '-';
-    this->operator<<(StringView(TempPtr, Temp.data() + Temp.size()));
+
+    return operator+=(StringView(TempPtr, Temp.data() + Temp.size()));
   }
 
 public:
   OutputBuffer(char *StartBuf, size_t Size)
       : Buffer(StartBuf), CurrentPosition(0), BufferCapacity(Size) {}
   OutputBuffer() = default;
   void reset(char *Buffer_, size_t BufferCapacity_) {
     CurrentPosition = 0;
     Buffer = Buffer_;
     BufferCapacity = BufferCapacity_;
   }
 
   /// If a ParameterPackExpansion (or similar type) is encountered, the offset
   /// into the pack that we're currently printing.
   unsigned CurrentPackIndex = std::numeric_limits<unsigned>::max();
   unsigned CurrentPackMax = std::numeric_limits<unsigned>::max();
 
   OutputBuffer &operator+=(StringView R) {
-    size_t Size = R.size();
-    if (Size == 0)
-      return *this;
+    if (size_t Size = R.size()) {
       grow(Size);
-    std::memmove(Buffer + CurrentPosition, R.begin(), Size);
+      std::memcpy(Buffer + CurrentPosition, R.begin(), Size);
       CurrentPosition += Size;
+    }
     return *this;
   }
 
   OutputBuffer &operator+=(char C) {
     grow(1);
     Buffer[CurrentPosition++] = C;
     return *this;
   }
 
-  OutputBuffer &operator<<(StringView R) { return (*this += R); }
-
   OutputBuffer prepend(StringView R) {
     size_t Size = R.size();
 
     grow(Size);
     std::memmove(Buffer + Size, Buffer, CurrentPosition);
     std::memcpy(Buffer, R.begin(), Size);
     CurrentPosition += Size;
 
     return *this;
   }
 
+  OutputBuffer &operator<<(StringView R) { return (*this += R); }
+
   OutputBuffer &operator<<(char C) { return (*this += C); }
 
   OutputBuffer &operator<<(long long N) {
-    if (N < 0)
-      writeUnsigned(static_cast<unsigned long long>(-N), true);
-    else
-      writeUnsigned(static_cast<unsigned long long>(N));
-    return *this;
+    return writeUnsigned(static_cast<unsigned long long>(std::abs(N)), N < 0);
   }
 
   OutputBuffer &operator<<(unsigned long long N) {
-    writeUnsigned(N, false);
-    return *this;
+    return writeUnsigned(N, false);
   }
 
   OutputBuffer &operator<<(long N) {
     return this->operator<<(static_cast<long long>(N));
   }
 
   OutputBuffer &operator<<(unsigned long N) {
     return this->operator<<(static_cast<unsigned long long>(N));