Avoid unnecessary arena allocations in `expand_pattern()`.

`expand_pattern()` has two callsites. One of them needs arena
allocation, but the other does not.

This commit moves the arena allocation out of the function. This avoids
the allocation of many 4 KiB page arena chunks that only hold a single
small allocation. It reduces the number of bytes allocated by up to 2%
for various benchmarks, albeit without only a very small improvement in
runtime.

0 files changed, 0 insertions, 0 deletions