miri: use tikv-jemalloc-sys from sysroot

This allows LTO to work when compiling jemalloc, which should yield a
small performance boost, and makes miri's behaviour here match clippy
and rustdoc.

Author: madsmtm

Cargo.toml

@@ -29,13 +29,6 @@ directories = "6"
 bitflags = "2.6"
 serde_json = { version = "1.0", optional = true }
 
-# Copied from `compiler/rustc/Cargo.toml`.
-# But only for some targets, it fails for others. Rustc configures this in its CI, but we can't
-# easily use that since we support of-tree builds.
-[target.'cfg(any(target_os = "linux", target_os = "macos"))'.dependencies.tikv-jemalloc-sys]
-version = "0.6.1"
-features = ['override_allocator_on_supported_platforms']
-
 [target.'cfg(unix)'.dependencies]
 libc = "0.2"
 # native-lib dependencies
@@ -75,6 +68,7 @@ stack-cache = []
 expensive-consistency-checks = ["stack-cache"]
 tracing = ["serde_json"]
 native-lib = ["dep:libffi", "dep:libloading", "dep:capstone", "dep:ipc-channel", "dep:nix", "dep:serde"]
+jemalloc = []
 
 [lints.rust.unexpected_cfgs]
 level = "warn"

src/bin/miri.rs

@@ -21,9 +21,13 @@ extern crate rustc_session;
 extern crate rustc_span;
 
 /// See docs in https://github.com/rust-lang/rust/blob/HEAD/compiler/rustc/src/main.rs
-/// and https://github.com/rust-lang/rust/pull/146627 for why we need this `use` statement.
-#[cfg(any(target_os = "linux", target_os = "macos"))]
-use tikv_jemalloc_sys as _;
+/// and https://github.com/rust-lang/rust/pull/146627 for why we need this.
+///
+/// FIXME(madsmtm): This is loaded from the sysroot that was built with the other `rustc` crates
+/// above, instead of via Cargo as you'd normally do. This is currently needed for LTO due to
+/// https://github.com/rust-lang/cc-rs/issues/1613.
+#[cfg(feature = "jemalloc")]
+extern crate tikv_jemalloc_sys as _;
 
 mod log;