[clang] Nits on uses of raw_string_ostream (NFC)

* Don't call raw_string_ostream::flush(), which is essentially a no-op.
* Strip unneeded calls to raw_string_ostream::str(), to avoid extra indirection.

Author: JOE1994

clang/lib/AST/APValue.cpp

@@ -947,7 +947,6 @@ std::string APValue::getAsString(const ASTContext &Ctx, QualType Ty) const {
   std::string Result;
   llvm::raw_string_ostream Out(Result);
   printPretty(Out, Ctx, Ty);
-  Out.flush();
   return Result;
 }
 

clang/lib/AST/DeclPrinter.cpp

@@ -629,7 +629,6 @@ static void printExplicitSpecifier(ExplicitSpecifier ES, llvm::raw_ostream &Out,
     EOut << ")";
   }
   EOut << " ";
-  EOut.flush();
   Out << Proto;
 }
 
@@ -790,7 +789,6 @@ void DeclPrinter::VisitFunctionDecl(FunctionDecl *D) {
         llvm::raw_string_ostream EOut(Proto);
         FT->getNoexceptExpr()->printPretty(EOut, nullptr, SubPolicy,
                                            Indentation, "\n", &Context);
-        EOut.flush();
         Proto += ")";
       }
     }

clang/lib/AST/Expr.cpp

@@ -612,7 +612,7 @@ std::string SYCLUniqueStableNameExpr::ComputeName(ASTContext &Context,
   llvm::raw_string_ostream Out(Buffer);
   Ctx->mangleCanonicalTypeName(Ty, Out);
 
-  return Out.str();
+  return Buffer;
 }
 
 PredefinedExpr::PredefinedExpr(SourceLocation L, QualType FNTy,
@@ -798,7 +798,6 @@ std::string PredefinedExpr::ComputeName(PredefinedIdentKind IK,
     FD->printQualifiedName(POut, Policy);
 
     if (IK == PredefinedIdentKind::Function) {
-      POut.flush();
       Out << Proto;
       return std::string(Name);
     }
@@ -880,15 +879,12 @@ std::string PredefinedExpr::ComputeName(PredefinedIdentKind IK,
       }
     }
 
-    TOut.flush();
     if (!TemplateParams.empty()) {
       // remove the trailing comma and space
       TemplateParams.resize(TemplateParams.size() - 2);
       POut << " [" << TemplateParams << "]";
     }
 
-    POut.flush();
-
     // Print "auto" for all deduced return types. This includes C++1y return
     // type deduction and lambdas. For trailing return types resolve the
     // decltype expression. Otherwise print the real type when this is

clang/lib/AST/Mangle.cpp

@@ -574,9 +574,9 @@ class ASTNameGenerator::Implementation {
     std::string BackendBuf;
     llvm::raw_string_ostream BOS(BackendBuf);
 
-    llvm::Mangler::getNameWithPrefix(BOS, FOS.str(), DL);
+    llvm::Mangler::getNameWithPrefix(BOS, FrontendBuf, DL);
 
-    return BOS.str();
+    return BackendBuf;
   }
 
   std::string getMangledThunk(const CXXMethodDecl *MD, const ThunkInfo &T,
@@ -589,9 +589,9 @@ class ASTNameGenerator::Implementation {
     std::string BackendBuf;
     llvm::raw_string_ostream BOS(BackendBuf);
 
-    llvm::Mangler::getNameWithPrefix(BOS, FOS.str(), DL);
+    llvm::Mangler::getNameWithPrefix(BOS, FrontendBuf, DL);
 
-    return BOS.str();
+    return BackendBuf;
   }
 };
 

clang/lib/AST/MicrosoftMangle.cpp

@@ -1396,7 +1396,7 @@ void MicrosoftCXXNameMangler::mangleNestedName(GlobalDecl GD) {
           Stream << '_' << Discriminator;
         if (ParameterDiscriminator)
           Stream << '_' << ParameterDiscriminator;
-        return Stream.str();
+        return Buffer;
       };
 
       unsigned Discriminator = BD->getBlockManglingNumber();

clang/lib/AST/StmtViz.cpp

@@ -34,15 +34,14 @@ struct DOTGraphTraits<const Stmt*> : public DefaultDOTGraphTraits {
   static std::string getNodeLabel(const Stmt* Node, const Stmt* Graph) {
 
 #ifndef NDEBUG
-    std::string OutSStr;
-    llvm::raw_string_ostream Out(OutSStr);
+    std::string OutStr;
+    llvm::raw_string_ostream Out(OutStr);
 
     if (Node)
       Out << Node->getStmtClassName();
     else
       Out << "<NULL>";
 
-    std::string OutStr = Out.str();
     if (OutStr[0] == '\n') OutStr.erase(OutStr.begin());
 
     // Process string output to make it nicer...

clang/lib/ASTMatchers/Dynamic/Registry.cpp

@@ -791,7 +791,7 @@ Registry::getMatcherCompletions(ArrayRef<ArgKind> AcceptedTypes) {
           TypedText += "\"";
       }
 
-      Completions.emplace_back(TypedText, OS.str(), MaxSpecificity);
+      Completions.emplace_back(TypedText, Decl, MaxSpecificity);
     }
   }
 

clang/lib/Analysis/CFG.cpp

@@ -6164,7 +6164,7 @@ void CFGBlock::printTerminatorJson(raw_ostream &Out, const LangOptions &LO,
 
   printTerminator(TempOut, LO);
 
-  Out << JsonFormat(TempOut.str(), AddQuotes);
+  Out << JsonFormat(Buf, AddQuotes);
 }
 
 // Returns true if by simply looking at the block, we can be sure that it
@@ -6345,10 +6345,9 @@ struct DOTGraphTraits<const CFG*> : public DefaultDOTGraphTraits {
   DOTGraphTraits(bool isSimple = false) : DefaultDOTGraphTraits(isSimple) {}
 
   static std::string getNodeLabel(const CFGBlock *Node, const CFG *Graph) {
-    std::string OutSStr;
-    llvm::raw_string_ostream Out(OutSStr);
+    std::string OutStr;
+    llvm::raw_string_ostream Out(OutStr);
     print_block(Out,Graph, *Node, *GraphHelper, false, false);
-    std::string& OutStr = Out.str();
 
     if (OutStr[0] == '\n') OutStr.erase(OutStr.begin());