[llvm] f0ef708 - [demangler][NFC] Utility header cleanups

[Nathan Sidwell via llvm-commits]

Author: Nathan Sidwell
Date: 2022-02-08T07:25:02-08:00
New Revision: f0ef708dc12eb7d3ec5d8af9abbae40bd27c07cd

URL: https://github.com/llvm/llvm-project/commit/f0ef708dc12eb7d3ec5d8af9abbae40bd27c07cd
DIFF: https://github.com/llvm/llvm-project/commit/f0ef708dc12eb7d3ec5d8af9abbae40bd27c07cd.diff

LOG: [demangler][NFC] Utility header cleanups

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.

Reviewed By: ChuanqiXu

Differential Revision: https://reviews.llvm.org/D119176

Added: 
    

Modified: 
    libcxxabi/src/demangle/Utility.h
    llvm/include/llvm/Demangle/Utility.h

Removed: 
    


################################################################################
diff  --git a/libcxxabi/src/demangle/Utility.h b/libcxxabi/src/demangle/Utility.h
index 3b27328522a6f..93ef2aae34ba8 100644
--- a/libcxxabi/src/demangle/Utility.h
+++ b/libcxxabi/src/demangle/Utility.h
@@ -45,25 +45,21 @@ class OutputBuffer {
     }
   }
 
-  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:
@@ -82,12 +78,11 @@ class OutputBuffer {
   unsigned CurrentPackMax = std::numeric_limits<unsigned>::max();
 
   OutputBuffer &operator+=(StringView R) {
-    size_t Size = R.size();
-    if (Size == 0)
-      return *this;
-    grow(Size);
-    std::memmove(Buffer + CurrentPosition, R.begin(), Size);
-    CurrentPosition += Size;
+    if (size_t Size = R.size()) {
+      grow(Size);
+      std::memcpy(Buffer + CurrentPosition, R.begin(), Size);
+      CurrentPosition += Size;
+    }
     return *this;
   }
 
@@ -97,8 +92,6 @@ class OutputBuffer {
     return *this;
   }
 
-  OutputBuffer &operator<<(StringView R) { return (*this += R); }
-
   OutputBuffer prepend(StringView R) {
     size_t Size = R.size();
 
@@ -110,19 +103,16 @@ class OutputBuffer {
     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) {

diff  --git a/llvm/include/llvm/Demangle/Utility.h b/llvm/include/llvm/Demangle/Utility.h
index 1cf7e8f1df458..58b1954ec82a5 100644
--- a/llvm/include/llvm/Demangle/Utility.h
+++ b/llvm/include/llvm/Demangle/Utility.h
@@ -45,25 +45,21 @@ class OutputBuffer {
     }
   }
 
-  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:
@@ -82,12 +78,11 @@ class OutputBuffer {
   unsigned CurrentPackMax = std::numeric_limits<unsigned>::max();
 
   OutputBuffer &operator+=(StringView R) {
-    size_t Size = R.size();
-    if (Size == 0)
-      return *this;
-    grow(Size);
-    std::memmove(Buffer + CurrentPosition, R.begin(), Size);
-    CurrentPosition += Size;
+    if (size_t Size = R.size()) {
+      grow(Size);
+      std::memcpy(Buffer + CurrentPosition, R.begin(), Size);
+      CurrentPosition += Size;
+    }
     return *this;
   }
 
@@ -97,8 +92,6 @@ class OutputBuffer {
     return *this;
   }
 
-  OutputBuffer &operator<<(StringView R) { return (*this += R); }
-
   OutputBuffer prepend(StringView R) {
     size_t Size = R.size();
 
@@ -110,19 +103,16 @@ class OutputBuffer {
     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) {