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, 8 insertions, 11 deletions

diff --git a/lib/Analysis/Analysis.cpp b/lib/Analysis/Analysis.cpp
index ade940a7d3..7b6397679d 100644
--- a/lib/Analysis/Analysis.cpp
+++ b/lib/Analysis/Analysis.cpp
@@ -75,8 +75,7 @@ void LLVMInitializeAnalysis(LLVMPassRegistryRef R) {
 LLVMBool LLVMVerifyModule(LLVMModuleRef M, LLVMVerifierFailureAction Action,
                           char **OutMessages) {
   raw_ostream *DebugOS = Action != LLVMReturnStatusAction ? &errs() : nullptr;
-  std::string Messages;
-  raw_string_ostream MsgsOS(Messages);
+  string_ostream MsgsOS;
 
   LLVMBool Result = verifyModule(*unwrap(M), OutMessages ? &MsgsOS : DebugOS);
 
@@ -88,7 +87,7 @@ LLVMBool LLVMVerifyModule(LLVMModuleRef M, LLVMVerifierFailureAction Action,
     report_fatal_error("Broken module found, compilation aborted!");
 
   if (OutMessages)
-    *OutMessages = strdup(MsgsOS.str().c_str());
+    *OutMessages = strndup(MsgsOS.str().data(), MsgsOS.str().size());
 
   return Result;
 }
diff --git a/lib/Analysis/BlockFrequencyInfo.cpp b/lib/Analysis/BlockFrequencyInfo.cpp
index 8ed8e3e4c2..7e702c3143 100644
--- a/lib/Analysis/BlockFrequencyInfo.cpp
+++ b/lib/Analysis/BlockFrequencyInfo.cpp
@@ -82,10 +82,9 @@ struct DOTGraphTraits<BlockFrequencyInfo*> : public DefaultDOTGraphTraits {
 
   std::string getNodeLabel(const BasicBlock *Node,
                            const BlockFrequencyInfo *Graph) {
-    std::string Result;
-    raw_string_ostream OS(Result);
+    string_ostream OS;
 
-    OS << Node->getName().str() << ":";
+    OS << Node->getName() << ":";
     switch (ViewBlockFreqPropagationDAG) {
     case GVDT_Fraction:
       Graph->printBlockFreq(OS, Node);
@@ -98,7 +97,7 @@ struct DOTGraphTraits<BlockFrequencyInfo*> : public DefaultDOTGraphTraits {
                        "never reach this point.");
     }
 
-    return Result;
+    return OS.str();
   }
 };
 
diff --git a/lib/Analysis/Lint.cpp b/lib/Analysis/Lint.cpp
index b14f3292e9..806a1fdee5 100644
--- a/lib/Analysis/Lint.cpp
+++ b/lib/Analysis/Lint.cpp
@@ -105,11 +105,10 @@ namespace {
     const DataLayout *DL;
     TargetLibraryInfo *TLI;
 
-    std::string Messages;
-    raw_string_ostream MessagesStr;
+    string_ostream MessagesStr;
 
     static char ID; // Pass identification, replacement for typeid
-    Lint() : FunctionPass(ID), MessagesStr(Messages) {
+    Lint() : FunctionPass(ID) {
       initializeLintPass(*PassRegistry::getPassRegistry());
     }
 
@@ -181,7 +180,7 @@ bool Lint::runOnFunction(Function &F) {
   TLI = &getAnalysis<TargetLibraryInfo>();
   visit(F);
   dbgs() << MessagesStr.str();
-  Messages.clear();
+  MessagesStr.clear();
   return false;
 }