Add lto feature

Author: 0xdeafbeef

CHANGELOG.md

@@ -6,6 +6,7 @@
 * Expose LRU cache options (athre0z)
 * Add `with_capacity_bytes` to `WriteBatch` (0xdeafbeef)
 * Add `set_compaction_pri` to `Options` (0xdeafbeef)
+* Add `lto` feature to enable link-time optimization using `linker-plugin-lto` (0xdeafbeef)
 
 ## [Breaking Changes]
 * Update jemalloc-sys to 0.6.0 (0xdeafbeef)

Cargo.toml

@@ -34,6 +34,7 @@ multi-threaded-cf = []
 serde1 = ["serde"]
 bindgen-runtime = ["librocksdb-sys/bindgen-runtime"]
 bindgen-static = ["librocksdb-sys/bindgen-static"]
+lto = ["librocksdb-sys/lto"]
 
 [dependencies]
 libc = "0.2"

README.md

@@ -77,3 +77,12 @@ features = ["bindgen-static", "snappy", "lz4", "zstd", "zlib", "bzip2"]
 ```
 
 Notice that `runtime` and `static` features are mutually exclusive, and won't compile if both enabled.
+
+## LTO
+Enable the `lto` feature to enable link-time optimization. It will compile rocksdb with `-flto` flag. This feature is disabled by default.
+
+> [!IMPORTANT]
+> You must use clang as `CC`. Eg. `CC=/usr/bin/clang CXX=/usr/bin/clang++`. Clang llvm version must be the same as the one used by rust compiler.
+> On the rust side you should use `RUSTFLAGS="-Clinker-plugin-lto -Clinker=clang -Clink-arg=-fuse-ld=lld"`.
+
+Check the [Rust documentation](https://doc.rust-lang.org/rustc/linker-plugin-lto.html) for more information.

librocksdb-sys/Cargo.toml

@@ -29,6 +29,7 @@ zstd = ["zstd-sys"]
 zlib = ["libz-sys"]
 bzip2 = ["bzip2-sys"]
 rtti = []
+lto = []
 
 [dependencies]
 libc = "0.2"

librocksdb-sys/build.rs

@@ -90,6 +90,17 @@ fn build_rocksdb() {
         config.define("USE_RTTI", Some("1"));
     }
 
+    // https://github.com/facebook/rocksdb/blob/be7703b27d9b3ac458641aaadf27042d86f6869c/Makefile#L195
+    if cfg!(feature = "lto") {
+        config.flag("-flto");
+        if !config.get_compiler().is_like_clang() {
+            panic!(
+                "LTO is only supported with clang. Either disable the `lto` feature\
+             or set `CC=/usr/bin/clang CXX=/usr/bin/clang++` environment variables."
+            );
+        }
+    }
+
     config.include(".");
     config.define("NDEBUG", Some("1"));