Auto merge of #108944 - cjgillot:clear-local-info, r=oli-obk

Wrap the whole LocalInfo in ClearCrossCrate.

MIR contains a lot of information about locals. The primary purpose of this information is the quality of borrowck diagnostics.

This PR aims to drop this information after MIR analyses are finished, ie. starting from post-cleanup runtime MIR.

1 files changed, 9 insertions, 3 deletions

diff --git a/compiler/rustc_mir_transform/src/lib.rs b/compiler/rustc_mir_transform/src/lib.rs
index b2c477c84d2..50c3023b02b 100644
--- a/compiler/rustc_mir_transform/src/lib.rs
+++ b/compiler/rustc_mir_transform/src/lib.rs
@@ -29,9 +29,9 @@ use rustc_hir::intravisit::{self, Visitor};
 use rustc_index::vec::IndexVec;
 use rustc_middle::mir::visit::Visitor as _;
 use rustc_middle::mir::{
-    traversal, AnalysisPhase, Body, ConstQualifs, Constant, LocalDecl, MirPass, MirPhase, Operand,
-    Place, ProjectionElem, Promoted, RuntimePhase, Rvalue, SourceInfo, Statement, StatementKind,
-    TerminatorKind,
+    traversal, AnalysisPhase, Body, ClearCrossCrate, ConstQualifs, Constant, LocalDecl, MirPass,
+    MirPhase, Operand, Place, ProjectionElem, Promoted, RuntimePhase, Rvalue, SourceInfo,
+    Statement, StatementKind, TerminatorKind,
 };
 use rustc_middle::ty::query::Providers;
 use rustc_middle::ty::{self, TyCtxt, TypeVisitableExt};
@@ -532,6 +532,12 @@ fn run_runtime_cleanup_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
         &[&lower_intrinsics::LowerIntrinsics, &simplify::SimplifyCfg::new("elaborate-drops")];
 
     pm::run_passes(tcx, body, passes, Some(MirPhase::Runtime(RuntimePhase::PostCleanup)));
+
+    // Clear this by anticipation. Optimizations and runtime MIR have no reason to look
+    // into this information, which is meant for borrowck diagnostics.
+    for decl in &mut body.local_decls {
+        decl.local_info = ClearCrossCrate::Clear;
+    }
 }
 
 fn run_optimization_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {