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Optimize CommandLineV1Flag type dispatch, validation, and FlagSaver. - #1983
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1. Replace `IsOfType<T>()` (up to 6 virtual `TypeId()` calls + 6 indirect `op_(kFastTypeId)` calls) in `ChangedDirectly`, `CommandLineV1Flag::Typename()`, and `CommandLineV1Flag::InvokeValidator()` with direct `op == &absl_flags::FlagOps<T>` pointer comparisons. 2. Add `!inited_.load(std::memory_order_acquire)` fast paths to `CommandLineV1Flag::ValidateDefaultValue()`, `IsModified()`, `IsSpecifiedOnCommandLine()`, and `HasValidatorFn()`, avoiding lazily allocating and locking ~8,000 `absl::Mutex`es during flag initialization. 3. Return a sentinel `V1FlagState` (`current_ == nullptr`) from `CommandLineV1Flag::SaveState()` when unmodified (`!inited_` and `!ChangedDirectly(op_, def_, cur_)`), avoiding `DataGuard()` mutex allocation/locking and ~8,000 `Clone(op_, cur_)` heap allocations/deletions per `FlagSaver` scope while preserving restoration across direct variable mutations and `SET_FLAGS_DEFAULT`. PiperOrigin-RevId: 989386175
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Optimize CommandLineV1Flag type dispatch, validation, and FlagSaver.
IsOfType<T>()(up to 6 virtualTypeId()calls + 6 indirectop_(kFastTypeId)calls) inChangedDirectly,CommandLineV1Flag::Typename(), andCommandLineV1Flag::InvokeValidator()with direct
op == &absl_flags::FlagOps<T>pointer comparisons.!inited_.load(std::memory_order_acquire)fast paths toCommandLineV1Flag::ValidateDefaultValue(),IsModified(),IsSpecifiedOnCommandLine(), andHasValidatorFn(), avoiding lazilyallocating and locking ~8,000
absl::Mutexes during flag initialization.V1FlagState(current_ == nullptr) fromCommandLineV1Flag::SaveState()when unmodified (!inited_and!ChangedDirectly(op_, def_, cur_)), avoidingDataGuard()mutexallocation/locking and ~8,000
Clone(op_, cur_)heap allocations/deletionsper
FlagSaverscope while preserving restoration across direct variablemutations and
SET_FLAGS_DEFAULT.