Rollup merge of #93870 - tmiasko:const-precise-live-drops-with-coverage, r=ecstatic-morse

Fix switch on discriminant detection in a presence of coverage counters

Fixes #93848.

r? ``@ecstatic-morse``

1 files changed, 18 insertions, 15 deletions

diff --git a/compiler/rustc_mir_dataflow/src/impls/mod.rs b/compiler/rustc_mir_dataflow/src/impls/mod.rs
index 9502c5d57d6..7d6a08d47da 100644
--- a/compiler/rustc_mir_dataflow/src/impls/mod.rs
+++ b/compiler/rustc_mir_dataflow/src/impls/mod.rs
@@ -706,24 +706,27 @@ fn switch_on_enum_discriminant<'mir, 'tcx>(
     block: &'mir mir::BasicBlockData<'tcx>,
     switch_on: mir::Place<'tcx>,
 ) -> Option<(mir::Place<'tcx>, &'tcx ty::AdtDef)> {
-    match block.statements.last().map(|stmt| &stmt.kind) {
-        Some(mir::StatementKind::Assign(box (lhs, mir::Rvalue::Discriminant(discriminated))))
-            if *lhs == switch_on =>
-        {
-            match &discriminated.ty(body, tcx).ty.kind() {
-                ty::Adt(def, _) => Some((*discriminated, def)),
-
-                // `Rvalue::Discriminant` is also used to get the active yield point for a
-                // generator, but we do not need edge-specific effects in that case. This may
-                // change in the future.
-                ty::Generator(..) => None,
-
-                t => bug!("`discriminant` called on unexpected type {:?}", t),
+    for statement in block.statements.iter().rev() {
+        match &statement.kind {
+            mir::StatementKind::Assign(box (lhs, mir::Rvalue::Discriminant(discriminated)))
+                if *lhs == switch_on =>
+            {
+                match &discriminated.ty(body, tcx).ty.kind() {
+                    ty::Adt(def, _) => return Some((*discriminated, def)),
+
+                    // `Rvalue::Discriminant` is also used to get the active yield point for a
+                    // generator, but we do not need edge-specific effects in that case. This may
+                    // change in the future.
+                    ty::Generator(..) => return None,
+
+                    t => bug!("`discriminant` called on unexpected type {:?}", t),
+                }
             }
+            mir::StatementKind::Coverage(_) => continue,
+            _ => return None,
         }
-
-        _ => None,
     }
+    None
 }
 
 struct OnMutBorrow<F>(F);