limit codegen-units to get the maximum optimization (#2138)

* Update Cargo.toml

* Update Cargo.toml

* Update Cargo.toml

Co-authored-by: Pierre Krieger <pierre.krieger1708@gmail.com>

* Update Cargo.toml

Co-authored-by: Pierre Krieger <pierre.krieger1708@gmail.com>
Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

Cargo.toml

@@ -126,11 +126,14 @@ opt-level = 3
 [profile.release]
 panic = "abort"
 lto = true
+# codegen-units set to 1 to avoid performance regressions when combined with LTO
+# See https://github.com/rust-lang/rust/issues/47745
+# https://doc.rust-lang.org/rustc/codegen-options/index.html#codegen-units
+codegen-units = 1
 #strip = "symbols"      # TODO: uncomment once stable
 
 [profile.min-size-release]
 inherits = "release"
-lto = true
 opt-level = "z"
 
 [[bench]]