Auto merge of #139088 - spastorino:ergonomic-ref-counting-2, r=nikomatsakis

Ergonomic ref counting: optimize away clones when possible

This PR build on top of https://github.com/rust-lang/rust/pull/134797. It optimizes codegen of ergonomic ref-counting when the type being `use`d is only known to be copy after monomorphization. We avoid codening a clone and generate bitwise copy instead.

RFC: https://github.com/rust-lang/rfcs/pull/3680
Tracking issue: https://github.com/rust-lang/rust/issues/132290
Project goal: https://github.com/rust-lang/rust-project-goals/issues/107

r? `@nikomatsakis`

This PR could better sit on top of https://github.com/rust-lang/rust/pull/131650 but as it did not land yet I've decided to just do minimal changes. It may be the case that doing what I'm doing regress the performance and we may need to go the full route of https://github.com/rust-lang/rust/pull/131650.
cc `@saethlin` in this regard.

1 files changed, 55 insertions, 0 deletions

diff --git a/tests/codegen/ergonomic-clones/closure.rs b/tests/codegen/ergonomic-clones/closure.rs
new file mode 100644
index 00000000000..b6fc8172641
--- /dev/null
+++ b/tests/codegen/ergonomic-clones/closure.rs
@@ -0,0 +1,55 @@
+//@ compile-flags: -C no-prepopulate-passes -Copt-level=0 -Zmir-opt-level=0
+
+#![crate_type = "lib"]
+
+#![feature(ergonomic_clones)]
+#![allow(incomplete_features)]
+
+use std::clone::UseCloned;
+
+pub fn ergonomic_clone_closure_move() -> String {
+    let s = String::from("hi");
+
+    // CHECK-NOT: ; call core::clone::impls::<impl core::clone::Clone for String>::clone
+    let cl = use || s;
+    cl()
+}
+
+#[derive(Clone)]
+struct Foo;
+
+impl UseCloned for Foo {}
+
+pub fn ergonomic_clone_closure_use_cloned() -> Foo {
+    let f = Foo;
+
+    // CHECK: ; call <closure::Foo as core::clone::Clone>::clone
+    let f1 = use || f;
+
+    // CHECK: ; call <closure::Foo as core::clone::Clone>::clone
+    let f2 = use || f;
+
+    f
+}
+
+pub fn ergonomic_clone_closure_copy() -> i32 {
+    let i = 1;
+
+    // CHECK-NOT: ; call core::clone::impls::<impl core::clone::Clone for i32>::clone
+    let i1 = use || i;
+
+    // CHECK-NOT: ; call core::clone::impls::<impl core::clone::Clone for i32>::clone
+    let i2 = use || i;
+
+    i
+}
+
+pub fn ergonomic_clone_closure_use_cloned_generics<T: UseCloned>(f: T) -> T {
+    // CHECK-NOT: ; call core::clone::impls::<impl core::clone::Clone for i32>::clone
+    let f1 = use || f;
+
+    // CHECK-NOT: ; call core::clone::impls::<impl core::clone::Clone for i32>::clone
+    let f2 = use || f;
+
+    f
+}