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[NFC][CLANG] Fix static analyzer bugs about unnecessary object copies with auto keyword #75082

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Dec 23, 2023
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[NFC][CLANG] Fix static analyzer bugs about unnecessary object copies with auto keyword #75082

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2 changes: 1 addition & 1 deletion clang/lib/CodeGen/BackendUtil.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -876,7 +876,7 @@ void EmitAssemblyHelper::RunOptimizationPipeline(
<< PluginFN << toString(PassPlugin.takeError());
}
}
for (auto PassCallback : CodeGenOpts.PassBuilderCallbacks)
for (const auto &PassCallback : CodeGenOpts.PassBuilderCallbacks)
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PassBuilderCallbacks is defined as:

clang/include/clang/Basic/CodeGenOptions.h:
404   /// List of pass builder callbacks.
405   std::vector<std::function<void(llvm::PassBuilder &)>> PassBuilderCallbacks;

In the case where a std::function element wraps a lambda, copies can be expensive, so such avoidance makes sense. The operator() member of std::function is already const qualified, so the addition of const doesn't effect the behavior, at least not in the current language standards. Such calls are valid even when a mutable lambda is wrapped. That arguably results in a const violation, so there have been some papers that argued for changes (N4348, P0045) but to my knowledge, the standard has not been changed.

This looks like a good change.

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Thank you @tahonermann for reviews and information!

PassCallback(PB);
#define HANDLE_EXTENSION(Ext) \
get##Ext##PluginInfo().RegisterPassBuilderCallbacks(PB);
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