Support: Add a raw_ostream::write_zeros() function. NFCI.

[pcc]

Summary

This will eventually replace MCObjectWriter::WriteZeros.

Part of PR37466.

[dblaikie]

Seems fine to me

cfe/trunk/lib/CodeGen/CoverageMappingGen.cpp

std::string RawCoverageMappings =
       llvm::join(CoverageMappings.begin(), CoverageMappings.end(), "");
   OS << RawCoverageMappings;
   size_t CoverageMappingSize = RawCoverageMappings.size();
   size_t FilenamesSize = OS.str().size() - CoverageMappingSize;
   // Append extra zeroes if necessary to ensure that the size of the filenames
   // and coverage mappings is a multiple of 8.
   if (size_t Rem = OS.str().size() % 8) {
     CoverageMappingSize += 8 - Rem;
-    for (size_t I = 0, S = 8 - Rem; I < S; ++I)
-      OS << '\0';
+    OS.write_zeros(8 - Rem);
   }
   auto *FilenamesAndMappingsVal =
       llvm::ConstantDataArray::getString(Ctx, OS.str(), false);
 
   // Create the deferred function records array
   auto RecordsTy =
       llvm::ArrayType::get(FunctionRecordTy, FunctionRecords.size());
   auto RecordsVal = llvm::ConstantArray::get(RecordsTy, FunctionRecords);

llvm/trunk/include/llvm/Support/raw_ostream.h

public:
   raw_ostream &operator<<(const formatv_object_base &);
 
   // Formatted output, see the format_bytes() function in Support/Format.h.
   raw_ostream &operator<<(const FormattedBytes &);
 
   /// indent - Insert 'NumSpaces' spaces.
   raw_ostream &indent(unsigned NumSpaces);
 
+  /// write_zeros - Insert 'NumZeros' nulls.
+  raw_ostream &write_zeros(unsigned NumZeros);
+
   /// Changes the foreground color of text that will be output from this point
   /// forward.
   /// @param Color ANSI color to use, the special SAVEDCOLOR can be used to
   /// change only the bold attribute, and keep colors untouched
   /// @param Bold bold/brighter text, default false
   /// @param BG if true change the background, default: change foreground
   /// @returns itself so it can be used within << invocations
   virtual raw_ostream &changeColor(enum Colors Color,

llvm/trunk/lib/Support/raw_ostream.cpp

while (!Bytes.empty()) {
     Bytes = Bytes.drop_front(Line.size());
     LineIndex += Line.size();
     if (LineIndex < Size)
       *this << '\n';
   }
   return *this;
 }
 
-/// indent - Insert 'NumSpaces' spaces.
-raw_ostream &raw_ostream::indent(unsigned NumSpaces) {
-  static const char Spaces[] = "                                "
-                               "                                "
-                               "                ";
+template <char C>
+static raw_ostream &write_padding(raw_ostream &OS, unsigned NumChars) {
+  static const char Chars[] = {C, C, C, C, C, C, C, C, C, C, C, C, C, C, C, C,
+                               C, C, C, C, C, C, C, C, C, C, C, C, C, C, C, C,
+                               C, C, C, C, C, C, C, C, C, C, C, C, C, C, C, C,
+                               C, C, C, C, C, C, C, C, C, C, C, C, C, C, C, C,
+                               C, C, C, C, C, C, C, C, C, C, C, C, C, C, C, C};
 
   // Usually the indentation is small, handle it with a fastpath.
-  if (NumSpaces < array_lengthof(Spaces))
-    return write(Spaces, NumSpaces);
+  if (NumChars < array_lengthof(Chars))
+    return OS.write(Chars, NumChars);
 
-  while (NumSpaces) {
-    unsigned NumToWrite = std::min(NumSpaces,
-                                   (unsigned)array_lengthof(Spaces)-1);
-    write(Spaces, NumToWrite);
-    NumSpaces -= NumToWrite;
+  while (NumChars) {
+    unsigned NumToWrite = std::min(NumChars,
+                                   (unsigned)array_lengthof(Chars)-1);
+    OS.write(Chars, NumToWrite);
+    NumChars -= NumToWrite;
   }
-  return *this;
+  return OS;
+}
+
+/// indent - Insert 'NumSpaces' spaces.
+raw_ostream &raw_ostream::indent(unsigned NumSpaces) {
+  return write_padding<' '>(*this, NumSpaces);
+}
+
+/// write_zeros - Insert 'NumZeros' nulls.
+raw_ostream &raw_ostream::write_zeros(unsigned NumZeros) {
+  return write_padding<'\0'>(*this, NumZeros);
 }
 
 void raw_ostream::anchor() {}
 
 //===----------------------------------------------------------------------===//
 //  Formatted Output
 //===----------------------------------------------------------------------===//