[vim/vim] eval: reduce string concat allocations (PR #19642)

[mattn]

Reduce allocations in string .= and .. operations by using vim_realloc() to grow the existing buffer in place, avoiding an alloc/copy/free cycle on every concatenation.

Operation	Before	After	Change
.= (append)	0.4877s	0.3957s	-19%
.. (concat)	0.1511s	0.1490s	(noise)

Note

The improvement is most visible with .= because the left-hand string grows repeatedly (e.g. let s .= 'x' in a loop). Without this patch, each iteration requires alloc/copy-all/free, making it O(n²) overall. vim_realloc() can often extend the buffer in place, avoiding the full copy. The .. benchmark concatenates two small fixed-size literals, so the copy cost is negligible regardless of the allocation strategy.

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You can view, comment on, or merge this pull request online at:

  https://github.com/vim/vim/pull/19642

Commit Summary

• a4aab3b eval: reduce string concat allocations

File Changes

(1 file)

• M src/eval.c (36)

Patch Links:

• https://github.com/vim/vim/pull/19642.patch
• https://github.com/vim/vim/pull/19642.diff

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