Rollup merge of rust-lang#93603 - connorff:compute-polonius-liveness-facts-flag, r=ecstatic-morse

Populate liveness facts when calling `get_body_with_borrowck_facts` without `-Z polonius`

For a new feature of [Flowistry](https://github.com/willcrichton/flowistry), a static-analysis tool, we need to obtain a `mir::Body`'s liveness facts using `get_body_with_borrowck_facts` (added in rust-lang#86977). We'd like to do this without passing `-Z polonius` as a compiler arg to avoid borrow checking the entire crate.

Support for doing this was added in rust-lang#88983, but the Polonius input facts used for liveness analysis are empty. This happens because the liveness input facts are populated in `liveness::generate` depending only on the value of `AllFacts::enabled` (which is toggled via compiler args).

This PR propagates the [`use_polonius`](https://github.com/rust-lang/rust/blob/8b09ba6a5d5c644fe0f1c27c7f9c80b334241707/compiler/rustc_borrowck/src/nll.rs#L168) flag to `liveness::generate` to support populating liveness facts without requiring the `-Z polonius` flag.

This fix is somewhat patchy - if it'd be better to add more widely-accessible state (like `AllFacts::enabled`) I'd be open to ideas!

Author: matthiaskrgr

compiler/rustc_borrowck/src/nll.rs

@@ -188,6 +188,7 @@ pub(crate) fn compute_regions<'cx, 'tcx>(
             move_data,
             elements,
             upvars,
+            use_polonius,
         );
 
     if let Some(all_facts) = &mut all_facts {

compiler/rustc_borrowck/src/type_check/liveness/mod.rs

@@ -37,6 +37,7 @@ pub(super) fn generate<'mir, 'tcx>(
     flow_inits: &mut ResultsCursor<'mir, 'tcx, MaybeInitializedPlaces<'mir, 'tcx>>,
     move_data: &MoveData<'tcx>,
     location_table: &LocationTable,
+    use_polonius: bool,
 ) {
     debug!("liveness::generate");
 
@@ -46,7 +47,7 @@ pub(super) fn generate<'mir, 'tcx>(
         &typeck.borrowck_context.constraints.outlives_constraints,
     );
     let live_locals = compute_live_locals(typeck.tcx(), &free_regions, &body);
-    let facts_enabled = AllFacts::enabled(typeck.tcx());
+    let facts_enabled = use_polonius || AllFacts::enabled(typeck.tcx());
 
     let polonius_drop_used = if facts_enabled {
         let mut drop_used = Vec::new();

compiler/rustc_borrowck/src/type_check/mod.rs

@@ -136,6 +136,7 @@ pub(crate) fn type_check<'mir, 'tcx>(
     move_data: &MoveData<'tcx>,
     elements: &Rc<RegionValueElements>,
     upvars: &[Upvar<'tcx>],
+    use_polonius: bool,
 ) -> MirTypeckResults<'tcx> {
     let implicit_region_bound = infcx.tcx.mk_region(ty::ReVar(universal_regions.fr_fn_body));
     let mut universe_causes = FxHashMap::default();
@@ -187,7 +188,15 @@ pub(crate) fn type_check<'mir, 'tcx>(
         &mut borrowck_context,
         |mut cx| {
             cx.equate_inputs_and_outputs(&body, universal_regions, &normalized_inputs_and_output);
-            liveness::generate(&mut cx, body, elements, flow_inits, move_data, location_table);
+            liveness::generate(
+                &mut cx,
+                body,
+                elements,
+                flow_inits,
+                move_data,
+                location_table,
+                use_polonius,
+            );
 
             translate_outlives_facts(&mut cx);
             let opaque_type_values = mem::take(&mut infcx.inner.borrow_mut().opaque_types);