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

[JOE1994]

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().

[llvmbot]

@llvm/pr-subscribers-llvm-ir
@llvm/pr-subscribers-llvm-adt
@llvm/pr-subscribers-llvm-analysis
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@llvm/pr-subscribers-llvm-binary-utilities

Author: Youngsuk Kim (JOE1994)

Changes

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().

---

Full diff: https://github.com/llvm/llvm-project/pull/96995.diff

6 Files Affected:

• (modified) llvm/include/llvm/ADT/FloatingPointMode.h (+1-1)
• (modified) llvm/include/llvm/Analysis/CFGPrinter.h (+3-4)
• (modified) llvm/include/llvm/Analysis/DDG.h (+4-4)
• (modified) llvm/include/llvm/DebugInfo/LogicalView/Core/LVSupport.h (+1-1)
• (modified) llvm/include/llvm/IR/ModuleSummaryIndex.h (+1-1)
• (modified) llvm/include/llvm/Object/MachO.h (+2-2)

diff --git a/llvm/include/llvm/ADT/FloatingPointMode.h b/llvm/include/llvm/ADT/FloatingPointMode.h
index 468de085d1bed..639d931ef88fe 100644
--- a/llvm/include/llvm/ADT/FloatingPointMode.h
+++ b/llvm/include/llvm/ADT/FloatingPointMode.h
@@ -176,7 +176,7 @@ struct DenormalMode {
     std::string storage;
     raw_string_ostream OS(storage);
     print(OS);
-    return OS.str();
+    return storage;
   }
 };
 
diff --git a/llvm/include/llvm/Analysis/CFGPrinter.h b/llvm/include/llvm/Analysis/CFGPrinter.h
index 590b4f064b1ee..2d2a84217985a 100644
--- a/llvm/include/llvm/Analysis/CFGPrinter.h
+++ b/llvm/include/llvm/Analysis/CFGPrinter.h
@@ -133,7 +133,7 @@ std::string SimpleNodeLabelString(const BasicBlockT *Node) {
   raw_string_ostream OS(Str);
 
   Node->printAsOperand(OS, false);
-  return OS.str();
+  return Str;
 }
 
 template <typename BasicBlockT>
@@ -148,7 +148,7 @@ std::string CompleteNodeLabelString(
   std::string Str;
   raw_string_ostream OS(Str);
   HandleBasicBlock(OS, *Node);
-  std::string OutStr = OS.str();
+  std::string OutStr(Str);
   // Remove "%" from BB name
   if (OutStr[0] == '%') {
     OutStr.erase(OutStr.begin());
@@ -247,7 +247,7 @@ struct DOTGraphTraits<DOTFuncInfo *> : public DefaultDOTGraphTraits {
       raw_string_ostream OS(Str);
       auto Case = *SwitchInst::ConstCaseIt::fromSuccessorIndex(SI, SuccNo);
       OS << Case.getCaseValue()->getValue();
-      return OS.str();
+      return Str;
     }
     return "";
   }
@@ -257,7 +257,6 @@ struct DOTGraphTraits<DOTFuncInfo *> : public DefaultDOTGraphTraits {
     if (NodeName.empty()) {
       raw_string_ostream NodeOS(NodeName);
       Node->printAsOperand(NodeOS, false);
-      NodeName = NodeOS.str();
       // Removing %
       NodeName.erase(NodeName.begin());
     }
diff --git a/llvm/include/llvm/Analysis/DDG.h b/llvm/include/llvm/Analysis/DDG.h
index bd559f3fb69b1..be5f746e31a57 100644
--- a/llvm/include/llvm/Analysis/DDG.h
+++ b/llvm/include/llvm/Analysis/DDG.h
@@ -467,16 +467,16 @@ DependenceGraphInfo<NodeType>::getDependenceString(const NodeType &Src,
   raw_string_ostream OS(Str);
   DependenceList Deps;
   if (!getDependencies(Src, Dst, Deps))
-    return OS.str();
+    return Str;
   interleaveComma(Deps, OS, [&](const std::unique_ptr<Dependence> &D) {
     D->dump(OS);
     // Remove the extra new-line character printed by the dump
     // method
-    if (OS.str().back() == '\n')
-      OS.str().pop_back();
+    if (Str.back() == '\n')
+      Str.pop_back();
   });
 
-  return OS.str();
+  return Str;
 }
 
 //===--------------------------------------------------------------------===//
diff --git a/llvm/include/llvm/DebugInfo/LogicalView/Core/LVSupport.h b/llvm/include/llvm/DebugInfo/LogicalView/Core/LVSupport.h
index 67089d9e7d41b..8269344fe6efe 100644
--- a/llvm/include/llvm/DebugInfo/LogicalView/Core/LVSupport.h
+++ b/llvm/include/llvm/DebugInfo/LogicalView/Core/LVSupport.h
@@ -110,7 +110,7 @@ inline std::string hexString(uint64_t Value, size_t Width = HEX_WIDTH) {
   std::string String;
   raw_string_ostream Stream(String);
   Stream << hexValue(Value, Width, false);
-  return Stream.str();
+  return String;
 }
 
 // Get a hexadecimal string representation for the given value.
diff --git a/llvm/include/llvm/IR/ModuleSummaryIndex.h b/llvm/include/llvm/IR/ModuleSummaryIndex.h
index a6bb261af7522..ecafb0e68fa7a 100644
--- a/llvm/include/llvm/IR/ModuleSummaryIndex.h
+++ b/llvm/include/llvm/IR/ModuleSummaryIndex.h
@@ -793,7 +793,7 @@ class FunctionSummary : public GlobalValueSummary {
       OS << ", hasUnknownCall: " << this->HasUnknownCall;
       OS << ", mustBeUnreachable: " << this->MustBeUnreachable;
       OS << ")";
-      return OS.str();
+      return Output;
     }
   };
 
diff --git a/llvm/include/llvm/Object/MachO.h b/llvm/include/llvm/Object/MachO.h
index 35350df78f8d4..61d05352ec75a 100644
--- a/llvm/include/llvm/Object/MachO.h
+++ b/llvm/include/llvm/Object/MachO.h
@@ -799,7 +799,7 @@ class MachOObjectFile : public ObjectFile {
       std::string ret;
       raw_string_ostream ss(ret);
       ss << format_hex(platform, 8, true);
-      return ss.str();
+      return ret;
     }
   }
 
@@ -814,7 +814,7 @@ class MachOObjectFile : public ObjectFile {
       std::string ret;
       raw_string_ostream ss(ret);
       ss << format_hex(tools, 8, true);
-      return ss.str();
+      return ret;
     }
   }
 

[JOE1994]

The following is the TODO comment I'm referring to:

llvm-project/llvm/include/llvm/Support/raw_ostream.h

Lines 676 to 679 in 8044158

	/// Returns the string's reference. In most cases it is better to simply use
	/// the underlying std::string directly.
	/// TODO: Consider removing this API.
	std::string &str() { return OS; }

[kazutakahirata]

Could we rename Str to OutStr and drop the copy construction?

Suggested change

	std::string Str;
	raw_string_ostream OS(Str);
	HandleBasicBlock(OS, *Node);
	std::string OutStr;
	raw_string_ostream OS(OutStr);
	HandleBasicBlock(OS, *Node);

[JOE1994]

Applied your feedback to follow-up commit. Thank you!

[MaskRay]

LGTM once kazutakahirata's comment is addressed.