Rollup merge of #108786 - saethlin:free-regions-check, r=oli-obk

Check for free regions in MIR validation

This turns https://github.com/rust-lang/rust/issues/108720 into a MIR validation failure that will reproduce without debug-assertions enabled.

```
error: internal compiler error: broken MIR in Item(WithOptConstParam { did: DefId(0:296 ~ futures_util[3805]::future::future::remote_handle::{impl#3}::poll), const_param_did: None }) (after pass ScalarReplacementOfAggregates) at bb0[0]:
                                Free regions in optimized runtime-post-cleanup MIR
  --> /home/ben/.cargo/registry/src/github.com-1ecc6299db9ec823/futures-util-0.3.26/src/future/future/remote_handle.rs:96:13
   |
96 |         let this = self.project();
   |             ^^^^
```

1 files changed, 0 insertions, 6 deletions

diff --git a/compiler/rustc_mir_transform/src/lib.rs b/compiler/rustc_mir_transform/src/lib.rs
index cdd28ae0c01..5fd923190ef 100644
--- a/compiler/rustc_mir_transform/src/lib.rs
+++ b/compiler/rustc_mir_transform/src/lib.rs
@@ -416,8 +416,6 @@ fn inner_mir_for_ctfe(tcx: TyCtxt<'_>, def: ty::WithOptConstParam<LocalDefId>) -
 
     pm::run_passes(tcx, &mut body, &[&ctfe_limit::CtfeLimit], None);
 
-    debug_assert!(!body.has_free_regions(), "Free regions in MIR for CTFE");
-
     body
 }
 
@@ -626,8 +624,6 @@ fn inner_optimized_mir(tcx: TyCtxt<'_>, did: LocalDefId) -> Body<'_> {
     debug!("body: {:#?}", body);
     run_optimization_passes(tcx, &mut body);
 
-    debug_assert!(!body.has_free_regions(), "Free regions in optimized MIR");
-
     body
 }
 
@@ -651,7 +647,5 @@ fn promoted_mir(
         run_analysis_to_runtime_passes(tcx, body);
     }
 
-    debug_assert!(!promoted.has_free_regions(), "Free regions in promoted MIR");
-
     tcx.arena.alloc(promoted)
 }