[llvm][Transforms] Avoid 'raw_string_ostream::str' (NFC)

Since `raw_string_ostream` doesn't own the string buffer, it is
desirable (in terms of memory safety) for users to directly reference
the string buffer rather than use `raw_string_ostream::str()`.

Work towards TODO comment to remove `raw_string_ostream::str()`.

Author: JOE1994

llvm/lib/Transforms/IPO/AttributorAttributes.cpp

@@ -8866,7 +8866,7 @@ struct AADenormalFPMathImpl : public AADenormalFPMath {
     if (Known.ModeF32.isValid())
       OS << " denormal-fp-math-f32=" << Known.ModeF32;
     OS << ']';
-    return OS.str();
+    return Str;
   }
 };
 
@@ -8979,7 +8979,7 @@ struct AAValueConstantRangeImpl : AAValueConstantRange {
     OS << " / ";
     getAssumed().print(OS);
     OS << ">";
-    return OS.str();
+    return Str;
   }
 
   /// Helper function to get a SCEV expr for the associated value at program
@@ -9656,7 +9656,7 @@ struct AAPotentialConstantValuesImpl : AAPotentialConstantValues {
     std::string Str;
     llvm::raw_string_ostream OS(Str);
     OS << getState();
-    return OS.str();
+    return Str;
   }
 
   /// See AbstractAttribute::updateImpl(...).
@@ -10778,7 +10778,7 @@ struct AAPotentialValuesImpl : AAPotentialValues {
     std::string Str;
     llvm::raw_string_ostream OS(Str);
     OS << getState();
-    return OS.str();
+    return Str;
   }
 
   template <typename AAType>

llvm/lib/Transforms/IPO/IROutliner.cpp

@@ -678,7 +678,7 @@ Function *IROutliner::createFunction(Module &M, OutlinableGroup &Group,
     Mg.getNameWithPrefix(MangledNameStream, F, false);
 
     DISubprogram *OutlinedSP = DB.createFunction(
-        Unit /* Context */, F->getName(), MangledNameStream.str(),
+        Unit /* Context */, F->getName(), Dummy,
         Unit /* File */,
         0 /* Line 0 is reserved for compiler-generated code. */,
         DB.createSubroutineType(

llvm/lib/Transforms/IPO/OpenMPOpt.cpp

@@ -1667,21 +1667,21 @@ struct OpenMPOpt {
       BP->print(Printer);
       Printer << Separator;
     }
-    LLVM_DEBUG(dbgs() << "\t\toffload_baseptrs: " << Printer.str() << "\n");
+    LLVM_DEBUG(dbgs() << "\t\toffload_baseptrs: " << ValuesStr << "\n");
     ValuesStr.clear();
 
     for (auto *P : OAs[1].StoredValues) {
       P->print(Printer);
       Printer << Separator;
     }
-    LLVM_DEBUG(dbgs() << "\t\toffload_ptrs: " << Printer.str() << "\n");
+    LLVM_DEBUG(dbgs() << "\t\toffload_ptrs: " << ValuesStr << "\n");
     ValuesStr.clear();
 
     for (auto *S : OAs[2].StoredValues) {
       S->print(Printer);
       Printer << Separator;
     }
-    LLVM_DEBUG(dbgs() << "\t\toffload_sizes: " << Printer.str() << "\n");
+    LLVM_DEBUG(dbgs() << "\t\toffload_sizes: " << ValuesStr << "\n");
   }
 
   /// Returns the instruction where the "wait" counterpart \p RuntimeCall can be

llvm/lib/Transforms/IPO/WholeProgramDevirt.cpp

@@ -1616,7 +1616,7 @@ std::string DevirtModule::getGlobalName(VTableSlot Slot,
   for (uint64_t Arg : Args)
     OS << '_' << Arg;
   OS << '_' << Name;
-  return OS.str();
+  return FullName;
 }
 
 bool DevirtModule::shouldExportConstantsAsAbsoluteSymbols() {

llvm/lib/Transforms/InstCombine/InstructionCombining.cpp

@@ -5080,7 +5080,7 @@ bool InstCombinerImpl::run() {
 #ifndef NDEBUG
     std::string OrigI;
 #endif
-    LLVM_DEBUG(raw_string_ostream SS(OrigI); I->print(SS); OrigI = SS.str(););
+    LLVM_DEBUG(raw_string_ostream SS(OrigI); I->print(SS););
     LLVM_DEBUG(dbgs() << "IC: Visiting: " << OrigI << '\n');
 
     if (Instruction *Result = visit(*I)) {

llvm/lib/Transforms/Instrumentation/PGOInstrumentation.cpp

@@ -2264,7 +2264,7 @@ static std::string getSimpleNodeName(const BasicBlock *Node) {
   std::string SimpleNodeName;
   raw_string_ostream OS(SimpleNodeName);
   Node->printAsOperand(OS, false);
-  return OS.str();
+  return SimpleNodeName;
 }
 
 void llvm::setProfMetadata(Module *M, Instruction *TI,

llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp

@@ -16211,7 +16211,7 @@ bool SLPVectorizerPass::tryToVectorizeList(ArrayRef<Value *> VL, BoUpSLP &R,
         Ty->print(rso);
         return OptimizationRemarkMissed(SV_NAME, "UnsupportedType", I0)
                << "Cannot SLP vectorize list: type "
-               << rso.str() + " is unsupported by vectorizer";
+               << TypeStr + " is unsupported by vectorizer";
       });
       return false;
     }