[flang] Tidy uses of raw_string_ostream (NFC)

As specified in the docs,
1) raw_string_ostream is always unbuffered and
2) the underlying buffer may be used directly

( 65b1361 for further reference )

Avoid unneeded calls to raw_string_ostream::str(), to avoid excess indirection.

Author: JOE1994

flang/include/flang/Parser/dump-parse-tree.h

@@ -875,7 +875,7 @@ class ParseTreeDumper {
       ss << x;
     }
     if (ss.tell()) {
-      return ss.str();
+      return buf;
     }
     if constexpr (std::is_same_v<T, Name>) {
       return x.source.ToString();

flang/lib/Evaluate/formatting.cpp

@@ -563,7 +563,7 @@ std::string ExpressionBase<RESULT>::AsFortran() const {
   std::string buf;
   llvm::raw_string_ostream ss{buf};
   AsFortran(ss);
-  return ss.str();
+  return buf;
 }
 
 template <typename RESULT>
@@ -604,7 +604,7 @@ static std::string DerivedTypeSpecAsFortran(
   if (ch != '(') {
     ss << ')';
   }
-  return ss.str();
+  return buf;
 }
 
 llvm::raw_ostream &StructureConstructor::AsFortran(llvm::raw_ostream &o) const {

flang/lib/Parser/prescan.cpp

@@ -1098,7 +1098,7 @@ void Prescanner::FortranInclude(const char *firstQuote) {
   const SourceFile *included{
       allSources_.Open(path, error, std::move(prependPath))};
   if (!included) {
-    Say(provenance, "INCLUDE: %s"_err_en_US, error.str());
+    Say(provenance, "INCLUDE: %s"_err_en_US, buf);
   } else if (included->bytes() > 0) {
     ProvenanceRange includeLineRange{
         provenance, static_cast<std::size_t>(p - nextLine_)};

flang/lib/Semantics/expression.cpp

@@ -3223,7 +3223,7 @@ void ExpressionAnalyzer::Analyze(const parser::CallStmt &callStmt) {
       llvm::raw_string_ostream dump{buf};
       parser::DumpTree(dump, callStmt);
       Say("Internal error: Expression analysis failed on CALL statement: %s"_err_en_US,
-          dump.str());
+          buf);
     }
   }
 }
@@ -3847,8 +3847,7 @@ MaybeExpr ExpressionAnalyzer::ExprOrVariable(
       std::string buf;
       llvm::raw_string_ostream dump{buf};
       parser::DumpTree(dump, x);
-      Say("Internal error: Expression analysis failed on: %s"_err_en_US,
-          dump.str());
+      Say("Internal error: Expression analysis failed on: %s"_err_en_US, buf);
     }
     return std::nullopt;
   }

flang/lib/Semantics/pointer-assignment.cpp

@@ -353,7 +353,7 @@ bool PointerAssignmentChecker::Check(const evaluate::Designator<T> &d) {
       std::string buf;
       llvm::raw_string_ostream ss{buf};
       d.AsFortran(ss);
-      Say(*m, description_, ss.str());
+      Say(*m, description_, buf);
     } else {
       Say(std::get<MessageFormattedText>(*msg));
     }

flang/lib/Semantics/scope.cpp

@@ -47,7 +47,7 @@ std::string EquivalenceObject::AsFortran() const {
   if (substringStart) {
     ss << '(' << *substringStart << ":)";
   }
-  return ss.str();
+  return buf;
 }
 
 Scope &Scope::MakeScope(Kind kind, Symbol *symbol) {

flang/lib/Semantics/tools.cpp

@@ -440,7 +440,7 @@ static void CheckMissingAnalysis(
     llvm::raw_string_ostream ss{buf};
     ss << "node has not been analyzed:\n";
     parser::DumpTree(ss, x);
-    common::die(ss.str().c_str());
+    common::die(buf.c_str());
   }
 }
 

flang/lib/Semantics/type.cpp

@@ -658,7 +658,7 @@ std::string DerivedTypeSpec::VectorTypeAsFortran() const {
   case (Fortran::semantics::DerivedTypeSpec::Category::DerivedType):
     Fortran::common::die("Vector element type not implemented");
   }
-  return ss.str();
+  return buf;
 }
 
 std::string DerivedTypeSpec::AsFortran() const {
@@ -694,7 +694,7 @@ std::string DerivedTypeSpec::AsFortran() const {
     }
     ss << ')';
   }
-  return ss.str();
+  return buf;
 }
 
 llvm::raw_ostream &operator<<(llvm::raw_ostream &o, const DerivedTypeSpec &x) {
@@ -771,7 +771,7 @@ std::string ParamValue::AsFortran() const {
       std::string buf;
       llvm::raw_string_ostream ss{buf};
       expr_->AsFortran(ss);
-      return ss.str();
+      return buf;
     } else {
       return "";
     }
@@ -795,7 +795,7 @@ static std::string KindAsFortran(const KindExpr &kind) {
   } else {
     kind.AsFortran(ss);
   }
-  return ss.str();
+  return buf;
 }
 
 std::string IntrinsicTypeSpec::AsFortran() const {

flang/unittests/Evaluate/real.cpp

@@ -158,10 +158,9 @@ template <typename R> void basicTests(int rm, Rounding rounding) {
       TEST(ivf.flags.empty())(ldesc);
       MATCH(x, ivf.value.ToUInt64())(ldesc);
       if (rounding.mode == RoundingMode::TiesToEven) { // to match stold()
-        std::string buf;
-        llvm::raw_string_ostream ss{buf};
+        std::string decimal;
+        llvm::raw_string_ostream ss{decimal};
         vr.value.AsFortran(ss, kind, false /*exact*/);
-        std::string decimal{ss.str()};
         const char *p{decimal.data()};
         MATCH(x, static_cast<std::uint64_t>(std::stold(decimal)))
         ("%s %s", ldesc, p);
@@ -424,22 +423,21 @@ void subsetTests(int pass, Rounding rounding, std::uint32_t opds) {
       ("%d IsInfinite(0x%jx)", pass, static_cast<std::intmax_t>(rj));
 
       static constexpr int kind{REAL::bits / 8};
-      std::string ssBuf, cssBuf;
-      llvm::raw_string_ostream ss{ssBuf};
+      std::string s, cssBuf;
+      llvm::raw_string_ostream ss{s};
       llvm::raw_string_ostream css{cssBuf};
       x.AsFortran(ss, kind, false /*exact*/);
-      std::string s{ss.str()};
       if (IsNaN(rj)) {
         css << "(0._" << kind << "/0.)";
-        MATCH(css.str(), s)
+        MATCH(cssBuf, s)
         ("%d invalid(0x%jx)", pass, static_cast<std::intmax_t>(rj));
       } else if (IsInfinite(rj)) {
         css << '(';
         if (IsNegative(rj)) {
           css << '-';
         }
         css << "1._" << kind << "/0.)";
-        MATCH(css.str(), s)
+        MATCH(cssBuf, s)
         ("%d overflow(0x%jx)", pass, static_cast<std::intmax_t>(rj));
       } else {
         const char *p = s.data();

flang/unittests/Frontend/CodeGenActionTest.cpp

@@ -103,7 +103,7 @@ TEST(CodeGenAction, GracefullyHandleLLVMConversionFailure) {
   action.setCurrentInput(file);
 
   consumeError(action.execute());
-  ASSERT_EQ(diagnosticsOS.str(),
+  ASSERT_EQ(diagnosticOutput,
       "error: Lowering to LLVM IR failed\n"
       "error: failed to create the LLVM module\n");
 }