Rollup merge of #90168 - tmiasko:const-qualif-storage, r=matthewjasper

Reset qualifs when a storage of a local ends

Reset qualifs when a storage of a local ends to ensure that the local qualifs
are affected by the state from previous loop iterations only if the local is
kept alive.

The change should be forward compatible with a stricter handling of indirect
assignments, since storage dead invalidates all existing pointers to the local.

Author: matthiaskrgr

compiler/rustc_const_eval/src/transform/check_consts/resolver.rs

@@ -4,7 +4,7 @@
 
 use rustc_index::bit_set::BitSet;
 use rustc_middle::mir::visit::Visitor;
-use rustc_middle::mir::{self, BasicBlock, Local, Location};
+use rustc_middle::mir::{self, BasicBlock, Local, Location, Statement, StatementKind};
 
 use std::marker::PhantomData;
 
@@ -120,6 +120,15 @@ where
         self.super_assign(place, rvalue, location);
     }
 
+    fn visit_statement(&mut self, statement: &Statement<'tcx>, location: Location) {
+        match statement.kind {
+            StatementKind::StorageDead(local) => {
+                self.qualifs_per_local.remove(local);
+            }
+            _ => self.super_statement(statement, location),
+        }
+    }
+
     fn visit_terminator(&mut self, terminator: &mir::Terminator<'tcx>, location: Location) {
         // The effect of assignment to the return place in `TerminatorKind::Call` is not applied
         // here; that occurs in `apply_call_return_effect`.

src/test/ui/consts/promoted-storage.rs

@@ -0,0 +1,20 @@
+// Check that storage statements reset local qualification.
+// check-pass
+use std::cell::Cell;
+
+const C: Option<Cell<u32>> = {
+    let mut c = None;
+    let mut i = 0;
+    while i == 0 {
+        let mut x = None;
+        c = x;
+        x = Some(Cell::new(0));
+        let _ = x;
+        i += 1;
+    }
+    c
+};
+
+fn main() {
+    let _: &'static _ = &C;
+}