perf(shirabe): use mimalloc as the global allocator

Profiling `create-project` showed glibc malloc/free accounting for about
41% of samples: the work is dominated by a very large number of small,
short-lived allocations, mostly from decoding repository JSON into
PhpMixed.

`create-project laravel/laravel`, offline against a warmed cache, all
three variants measured in one hyperfine run (8 runs each, identical
composer.lock):

  glibc      3.633 s +- 0.023   (user 3.580 s, sys 2.255 s)
  mimalloc   3.096 s +- 0.054   (user 3.004 s, sys 2.315 s)   -14.8%
  jemalloc   3.177 s +- 0.028   (user 3.136 s, sys 2.285 s)   -12.5%

The gain is entirely in user time; system time is unchanged, so the
extraction and file-writing half of the run is unaffected. Peak RSS drops
slightly, from 267 MB to 257 MB. mimalloc wins over jemalloc and, unlike
jemalloc, needs no C build of its own at every profile.

The allocator is declared in the library rather than in `main.rs` so that
the test and benchmark binaries, which link this crate but not `main.rs`,
run against the allocator the binary ships with.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

1 files changed, 4 insertions, 0 deletions

diff --git a/crates/shirabe/src/lib.rs b/crates/shirabe/src/lib.rs
index 9daf2188..3b142e74 100644
--- a/crates/shirabe/src/lib.rs
+++ b/crates/shirabe/src/lib.rs
@@ -25,6 +25,10 @@ pub mod self_update;
 pub mod signal;
 pub mod util;
 
+// Declared here to use this allocator in all binaries including tests and benches.
+#[global_allocator]
+static GLOBAL: mimalloc::MiMalloc = mimalloc::MiMalloc;
+
 // InstalledVersions is intentionally unported to Rust. It is a runtime API for plugins and project
 // code, never read by Composer itself. Its real state is stored in PHP's InstalledVersions class.
 // See also `__shirabe_installed_versions_reload` in crates/shirabe-php-rpc/php/worker.php.