Introduce a string_ostream string builder facilty

string_ostream is a safe and efficient string builder that combines opaque
stack storage with a built-in ostream interface.

small_string_ostream<bytes> additionally permits an explicit stack storage size
other than the default 128 bytes to be provided. Beyond that, storage is
transferred to the heap.

This convenient class can be used in most places an
std::string+raw_string_ostream pair or SmallString<>+raw_svector_ostream pair
would previously have been used, in order to guarantee consistent access
without byte truncation.

The patch also converts much of LLVM to use the new facility. These changes
include several probable bug fixes for truncated output, a programming error
that's no longer possible with the new interface.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@211749 91177308-0d34-0410-b5e6-96231b3b80d8

3 files changed, 15 insertions, 19 deletions

diff --git a/utils/FileCheck/FileCheck.cpp b/utils/FileCheck/FileCheck.cpp
index 978e05f4f2c..2c33e6896b7 100644
--- a/utils/FileCheck/FileCheck.cpp
+++ b/utils/FileCheck/FileCheck.cpp
@@ -458,8 +458,7 @@ void Pattern::PrintFailureInfo(const SourceMgr &SM, StringRef Buffer,
   // variable values.
   if (!VariableUses.empty()) {
     for (unsigned i = 0, e = VariableUses.size(); i != e; ++i) {
-      SmallString<256> Msg;
-      raw_svector_ostream OS(Msg);
+      small_string_ostream<256> OS;
       StringRef Var = VariableUses[i].first;
       if (Var[0] == '@') {
         std::string Value;
diff --git a/utils/TableGen/CodeEmitterGen.cpp b/utils/TableGen/CodeEmitterGen.cpp
index 4d0c0ca8e70..5e27d45b156 100644
--- a/utils/TableGen/CodeEmitterGen.cpp
+++ b/utils/TableGen/CodeEmitterGen.cpp
@@ -319,8 +319,7 @@ void CodeEmitterGen::run(raw_ostream &o) {
 
   // Default case: unhandled opcode
   o << "  default:\n"
-    << "    std::string msg;\n"
-    << "    raw_string_ostream Msg(msg);\n"
+    << "    string_ostream Msg;\n"
     << "    Msg << \"Not supported instr: \" << MI;\n"
     << "    report_fatal_error(Msg.str());\n"
     << "  }\n"
diff --git a/utils/yaml-bench/YAMLBench.cpp b/utils/yaml-bench/YAMLBench.cpp
index 39b8f72ecc5..c3c7c152c2c 100644
--- a/utils/yaml-bench/YAMLBench.cpp
+++ b/utils/yaml-bench/YAMLBench.cpp
@@ -166,23 +166,21 @@ static void benchmark( llvm::TimerGroup &Group
 }
 
 static std::string createJSONText(size_t MemoryMB, unsigned ValueSize) {
-  std::string JSONText;
-  llvm::raw_string_ostream Stream(JSONText);
-  Stream << "[\n";
+  llvm::string_ostream OS;
+  OS << "[\n";
   size_t MemoryBytes = MemoryMB * 1024 * 1024;
-  while (JSONText.size() < MemoryBytes) {
-    Stream << " {\n"
-           << "  \"key1\": \"" << std::string(ValueSize, '*') << "\",\n"
-           << "  \"key2\": \"" << std::string(ValueSize, '*') << "\",\n"
-           << "  \"key3\": \"" << std::string(ValueSize, '*') << "\"\n"
-           << " }";
-    Stream.flush();
-    if (JSONText.size() < MemoryBytes) Stream << ",";
-    Stream << "\n";
+  while (OS.tell() < MemoryBytes) {
+    OS << " {\n"
+       << "  \"key1\": \"" << std::string(ValueSize, '*') << "\",\n"
+       << "  \"key2\": \"" << std::string(ValueSize, '*') << "\",\n"
+       << "  \"key3\": \"" << std::string(ValueSize, '*') << "\"\n"
+       << " }";
+    if (OS.tell() < MemoryBytes)
+      OS << ",";
+    OS << "\n";
   }
-  Stream << "]\n";
-  Stream.flush();
-  return JSONText;
+  OS << "]\n";
+  return OS.str();
 }
 
 int main(int argc, char **argv) {