Auto merge of #68414 - michaelwoerister:share-drop-glue, r=alexcrichton

Also share drop-glue when compiling with -Zshare-generics (i.e. at opt-level=0)

This PR adds drop-glue to the set of monomorphizations that can be shared across crates via `-Zshare-generics`.

This version of the PR might have detrimental effects on performance as it makes lots of stuff dependent on a single query results (`upstream_monomorphizations_for(def_id_of_drop_in_place)`). That should be fixable but let's do a perf run first.

Potentially fixes issue https://github.com/rust-lang/rust/issues/64140. (cc @alexcrichton)
The changes here are related to @matthewjasper's https://github.com/rust-lang/rust/pull/67332 but should be mostly orthogonal.

r? @ghost

src/test/codegen-units/partitioning/auxiliary/shared_generics_aux.rs

@@ -1,4 +1,6 @@
-// compile-flags:-Zshare-generics=yes
+// NOTE: We always compile this test with -Copt-level=0 because higher opt-levels
+//       prevent drop-glue from participating in share-generics.
+// compile-flags:-Zshare-generics=yes -Copt-level=0
 // no-prefer-dynamic
 
 #![crate_type="rlib"]
@@ -8,5 +10,17 @@ pub fn generic_fn<T>(x: T, y: T) -> (T, T) {
 }
 
 pub fn use_generic_fn_f32() -> (f32, f32) {
+    // This line causes drop glue for Foo to be instantiated. We want to make
+    // sure that this crate exports an instance to be re-used by share-generics.
+    let _ = Foo(0);
+
     generic_fn(0.0f32, 1.0f32)
 }
+
+pub struct Foo(pub u32);
+
+impl Drop for Foo {
+    fn drop(&mut self) {
+        println!("foo");
+    }
+}

src/test/codegen-units/partitioning/shared-generics.rs

@@ -1,6 +1,8 @@
 // ignore-tidy-linelength
 // no-prefer-dynamic
-// compile-flags:-Zprint-mono-items=eager -Zshare-generics=yes -Zincremental=tmp/partitioning-tests/shared-generics-exe
+// NOTE: We always compile this test with -Copt-level=0 because higher opt-levels
+//       prevent drop-glue from participating in share-generics.
+// compile-flags:-Zprint-mono-items=eager -Zshare-generics=yes -Zincremental=tmp/partitioning-tests/shared-generics-exe -Copt-level=0
 
 #![crate_type="rlib"]
 
@@ -16,6 +18,10 @@ pub fn foo() {
     // This should not generate a monomorphization because it's already
     // available in `shared_generics_aux`.
     let _ = shared_generics_aux::generic_fn(0.0f32, 3.0f32);
-}
 
-// MONO_ITEM drop-glue i8
+    // The following line will drop an instance of `Foo`, generating a call to
+    // Foo's drop-glue function. However, share-generics should take care of
+    // reusing the drop-glue from the upstream crate, so we do not expect a
+    // mono item for the drop-glue
+    let _ = shared_generics_aux::Foo(1);
+}