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As a follow-up to #113852, this PR optimizes the performance of the `insert(const_iterator pos, InputIt first, InputIt last)` function for `input_iterator`-pair inputs in `std::vector` for cases where reallocation occurs during insertion. Additionally, this optimization enhances exception safety by replacing the traditional `try-catch` mechanism with a modern exception guard for the `insert` function. The optimization targets cases where insertion trigger reallocation. In scenarios without reallocation, the implementation remains unchanged. Previous implementation ----------------------- The previous implementation of `insert` is inefficient in reallocation scenarios because it performs the following steps separately: - `reserve()`: This leads to the first round of relocating old elements to new memory; - `rotate()`: This leads to the second round of reorganizing the existing elements; - Move-forward: Moves the elements after the insertion position to their final positions. - Insert: performs the actual insertion. This approach results in a lot of redundant operations, requiring the elements to undergo three rounds of relocations/reorganizations to be placed in their final positions. Proposed implementation ----------------------- The proposed implementation jointly optimize the above 4 steps in the previous implementation such that each element is placed in its final position in just one round of relocation. Specifically, this optimization reduces the total cost from 2 relocations + 1 std::rotate call to just 1 relocation, without needing to call `std::rotate`, thereby significantly improving overall performance.
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