[PATCH] D115374: [NFC][clang] Return std::strings built from raw_string_ostreams more efficiently

[Logan Smith via Phabricator via cfe-commits]

logan-5 created this revision.
logan-5 added a reviewer: aaron.ballman.
logan-5 added a project: clang.
Herald added subscribers: abrachet, ctetreau, dexonsmith, martong.
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Returning `OS.str()` is guaranteed to copy the underlying string, whereas `OS.flush(); return Underlying;` makes `Underlying` a candidate for NRVO, or at worst, implicit move.

To keep this kind of inefficiency at bay in the future, the fast code should probably be made easier to type than the slow code (as it's currently the opposite). Perhaps this could be solved by:

- making `raw_string_ostream` guarantee+document that it does not need to be `flush()`ed (similar to `raw_svector_ostream`), //and/or//
- making `raw_string_ostream::str()` return a `StringRef` rather than `std::string&`, to discourage using it to initialize `std::string`s

Implementing those two ideas would make simply `return Underlying;` the natural, correct, and efficient choice. They are, however, out of scope for this patch.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D115374

Files:
  clang/include/clang/StaticAnalyzer/Checkers/SValExplainer.h
  clang/include/clang/Testing/TestClangConfig.h
  clang/lib/AST/ASTDiagnostic.cpp
  clang/lib/AST/AttrImpl.cpp
  clang/lib/AST/Decl.cpp
  clang/lib/AST/DeclarationName.cpp
  clang/lib/AST/OpenMPClause.cpp
  clang/lib/ASTMatchers/Dynamic/Diagnostics.cpp
  clang/lib/Analysis/AnalysisDeclContext.cpp
  clang/lib/Basic/SourceLocation.cpp
  clang/lib/Basic/Version.cpp
  clang/lib/Frontend/CompilerInvocation.cpp
  clang/lib/Frontend/TestModuleFileExtension.cpp
  clang/lib/Rewrite/HTMLRewrite.cpp
  clang/lib/Sema/CodeCompleteConsumer.cpp
  clang/lib/Sema/SemaAttr.cpp
  clang/lib/StaticAnalyzer/Checkers/FuchsiaHandleChecker.cpp
  clang/lib/StaticAnalyzer/Core/HTMLDiagnostics.cpp
  clang/lib/StaticAnalyzer/Core/MemRegion.cpp
  clang/lib/Tooling/Syntax/Tokens.cpp
  clang/lib/Tooling/Syntax/Tree.cpp
  clang/tools/clang-fuzzer/handle-llvm/handle_llvm.cpp
  clang/unittests/AST/ASTTraverserTest.cpp
  clang/unittests/Analysis/MacroExpansionContextTest.cpp
  clang/unittests/Tooling/Syntax/TreeTest.cpp

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