Rollup merge of rust-lang#88983 - willcrichton:allow-single-polonius-call, r=ecstatic-morse

Allow calling `get_body_with_borrowck_facts` without `-Z polonius`

For my [static analysis tool](https://github.com/willcrichton/flowistry), I need to access the set of outlives-constraints. Recently, rust-lang#86977 merged a way to access these facts via Polonius. However, the merged implementation requires `-Z polonius` to be provided to use this feature. This uses Polonius for borrow checking on the entire crate, which as described [here](https://rust-lang.zulipchat.com/#narrow/stream/186049-t-compiler.2Fwg-polonius/topic/Polonius.20performance.20in.20a.20rustc.20plugin/near/251301631), is very slow.

This PR allows `get_body_with_borrowck_facts` to be called without `-Z polonius`. This is essential for my tool to run in a sensible length of time. This is a temporary patch as the Polonius-related APIs develop -- I can update my code as future changes happen.

Additionally, this PR also makes public two APIs that were previously public but then became private after `rustc_mir` got broken up: `rustc_mir_dataflow::framework::graphviz` and `rustc_mir_transform::MirPass`. I need both of these for my analysis tool. (I can break this change into a separate PR if necessary.)

Author: Manishearth

compiler/rustc_borrowck/src/consumers.rs

@@ -14,16 +14,16 @@ pub use super::{
 };
 
 /// This function computes Polonius facts for the given body. It makes a copy of
-/// the body because it needs to regenerate the region identifiers.
+/// the body because it needs to regenerate the region identifiers. This function
+/// should never be invoked during a typical compilation session due to performance
+/// issues with Polonius.
 ///
 /// Note:
 /// *   This function will panic if the required body was already stolen. This
 ///     can, for example, happen when requesting a body of a `const` function
 ///     because they are evaluated during typechecking. The panic can be avoided
 ///     by overriding the `mir_borrowck` query. You can find a complete example
 ///     that shows how to do this at `src/test/run-make/obtain-borrowck/`.
-/// *   This function will also panic if computation of Polonius facts
-///     (`-Zpolonius` flag) is not enabled.
 ///
 /// *   Polonius is highly unstable, so expect regular changes in its signature or other details.
 pub fn get_body_with_borrowck_facts<'tcx>(

compiler/rustc_borrowck/src/lib.rs

@@ -154,11 +154,6 @@ fn do_mir_borrowck<'a, 'tcx>(
 
     debug!("do_mir_borrowck(def = {:?})", def);
 
-    assert!(
-        !return_body_with_facts || infcx.tcx.sess.opts.debugging_opts.polonius,
-        "borrowck facts can be requested only when Polonius is enabled"
-    );
-
     let tcx = infcx.tcx;
     let param_env = tcx.param_env(def.did);
     let id = tcx.hir().local_def_id_to_hir_id(def.did);
@@ -235,6 +230,8 @@ fn do_mir_borrowck<'a, 'tcx>(
     let borrow_set =
         Rc::new(BorrowSet::build(tcx, body, locals_are_invalidated_at_exit, &mdpe.move_data));
 
+    let use_polonius = return_body_with_facts || infcx.tcx.sess.opts.debugging_opts.polonius;
+
     // Compute non-lexical lifetimes.
     let nll::NllOutput {
         regioncx,
@@ -254,6 +251,7 @@ fn do_mir_borrowck<'a, 'tcx>(
         &mdpe.move_data,
         &borrow_set,
         &upvars,
+        use_polonius,
     );
 
     // Dump MIR results into a file, if that is enabled. This let us

compiler/rustc_borrowck/src/nll.rs

@@ -164,8 +164,10 @@ pub(crate) fn compute_regions<'cx, 'tcx>(
     move_data: &MoveData<'tcx>,
     borrow_set: &BorrowSet<'tcx>,
     upvars: &[Upvar<'tcx>],
+    use_polonius: bool,
 ) -> NllOutput<'tcx> {
-    let mut all_facts = AllFacts::enabled(infcx.tcx).then_some(AllFacts::default());
+    let mut all_facts =
+        (use_polonius || AllFacts::enabled(infcx.tcx)).then_some(AllFacts::default());
 
     let universal_regions = Rc::new(universal_regions);
 
@@ -281,7 +283,7 @@ pub(crate) fn compute_regions<'cx, 'tcx>(
             all_facts.write_to_dir(dir_path, location_table).unwrap();
         }
 
-        if infcx.tcx.sess.opts.debugging_opts.polonius {
+        if use_polonius {
             let algorithm =
                 env::var("POLONIUS_ALGORITHM").unwrap_or_else(|_| String::from("Hybrid"));
             let algorithm = Algorithm::from_str(&algorithm).unwrap();

compiler/rustc_mir_dataflow/src/lib.rs

@@ -28,8 +28,8 @@ pub use self::drop_flag_effects::{
     on_lookup_result_bits,
 };
 pub use self::framework::{
-    fmt, lattice, visit_results, Analysis, AnalysisDomain, Backward, Direction, Engine, Forward,
-    GenKill, GenKillAnalysis, JoinSemiLattice, Results, ResultsCursor, ResultsRefCursor,
+    fmt, graphviz, lattice, visit_results, Analysis, AnalysisDomain, Backward, Direction, Engine,
+    Forward, GenKill, GenKillAnalysis, JoinSemiLattice, Results, ResultsCursor, ResultsRefCursor,
     ResultsVisitable, ResultsVisitor,
 };
 

compiler/rustc_mir_transform/src/lib.rs

@@ -76,7 +76,7 @@ mod unreachable_prop;
 use rustc_const_eval::transform::check_consts;
 use rustc_const_eval::transform::promote_consts;
 use rustc_const_eval::transform::validate;
-use rustc_const_eval::transform::MirPass;
+pub use rustc_const_eval::transform::MirPass;
 use rustc_mir_dataflow::rustc_peek;
 
 pub fn provide(providers: &mut Providers) {