From 532080cfcccdfd853008c4452b283130b544c675 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Tomasz=20Mi=C4=85sko?= <tomasz.miasko@gmail.com>
Date: Sun, 17 Dec 2023 00:00:00 +0000
Subject: [PATCH] Stricter check for a use of locals without storage

---
 compiler/rustc_mir_transform/src/lint.rs | 28 ++++++++++++++--------
 tests/ui/mir/lint/no-storage.rs          | 30 ++++++++++++++++++++++++
 2 files changed, 48 insertions(+), 10 deletions(-)
 create mode 100644 tests/ui/mir/lint/no-storage.rs

diff --git a/compiler/rustc_mir_transform/src/lint.rs b/compiler/rustc_mir_transform/src/lint.rs
index d7380b4e04b..3940d0ddbf3 100644
--- a/compiler/rustc_mir_transform/src/lint.rs
+++ b/compiler/rustc_mir_transform/src/lint.rs
@@ -5,7 +5,7 @@
 use rustc_middle::mir::visit::{PlaceContext, Visitor};
 use rustc_middle::mir::*;
 use rustc_middle::ty::TyCtxt;
-use rustc_mir_dataflow::impls::MaybeStorageLive;
+use rustc_mir_dataflow::impls::{MaybeStorageDead, MaybeStorageLive};
 use rustc_mir_dataflow::storage::always_storage_live_locals;
 use rustc_mir_dataflow::{Analysis, ResultsCursor};
 use std::borrow::Cow;
@@ -13,7 +13,13 @@
 pub fn lint_body<'tcx>(tcx: TyCtxt<'tcx>, body: &Body<'tcx>, when: String) {
     let reachable_blocks = traversal::reachable_as_bitset(body);
     let always_live_locals = &always_storage_live_locals(body);
-    let storage_liveness = MaybeStorageLive::new(Cow::Borrowed(always_live_locals))
+
+    let maybe_storage_live = MaybeStorageLive::new(Cow::Borrowed(always_live_locals))
+        .into_engine(tcx, body)
+        .iterate_to_fixpoint()
+        .into_results_cursor(body);
+
+    let maybe_storage_dead = MaybeStorageDead::new(Cow::Borrowed(always_live_locals))
         .into_engine(tcx, body)
         .iterate_to_fixpoint()
         .into_results_cursor(body);
@@ -25,7 +31,8 @@ pub fn lint_body<'tcx>(tcx: TyCtxt<'tcx>, body: &Body<'tcx>, when: String) {
         is_fn_like: tcx.def_kind(body.source.def_id()).is_fn_like(),
         always_live_locals,
         reachable_blocks,
-        storage_liveness,
+        maybe_storage_live,
+        maybe_storage_dead,
     }
     .visit_body(body);
 }
@@ -37,7 +44,8 @@ struct Lint<'a, 'tcx> {
     is_fn_like: bool,
     always_live_locals: &'a BitSet<Local>,
     reachable_blocks: BitSet<BasicBlock>,
-    storage_liveness: ResultsCursor<'a, 'tcx, MaybeStorageLive<'a>>,
+    maybe_storage_live: ResultsCursor<'a, 'tcx, MaybeStorageLive<'a>>,
+    maybe_storage_dead: ResultsCursor<'a, 'tcx, MaybeStorageDead<'a>>,
 }
 
 impl<'a, 'tcx> Lint<'a, 'tcx> {
@@ -60,8 +68,8 @@ fn fail(&self, location: Location, msg: impl AsRef<str>) {
 impl<'a, 'tcx> Visitor<'tcx> for Lint<'a, 'tcx> {
     fn visit_local(&mut self, local: Local, context: PlaceContext, location: Location) {
         if self.reachable_blocks.contains(location.block) && context.is_use() {
-            self.storage_liveness.seek_after_primary_effect(location);
-            if !self.storage_liveness.get().contains(local) {
+            self.maybe_storage_dead.seek_after_primary_effect(location);
+            if self.maybe_storage_dead.get().contains(local) {
                 self.fail(location, format!("use of local {local:?}, which has no storage here"));
             }
         }
@@ -71,8 +79,8 @@ fn visit_statement(&mut self, statement: &Statement<'tcx>, location: Location) {
         match statement.kind {
             StatementKind::StorageLive(local) => {
                 if self.reachable_blocks.contains(location.block) {
-                    self.storage_liveness.seek_before_primary_effect(location);
-                    if self.storage_liveness.get().contains(local) {
+                    self.maybe_storage_live.seek_before_primary_effect(location);
+                    if self.maybe_storage_live.get().contains(local) {
                         self.fail(
                             location,
                             format!("StorageLive({local:?}) which already has storage here"),
@@ -90,8 +98,8 @@ fn visit_terminator(&mut self, terminator: &Terminator<'tcx>, location: Location
         match terminator.kind {
             TerminatorKind::Return => {
                 if self.is_fn_like && self.reachable_blocks.contains(location.block) {
-                    self.storage_liveness.seek_after_primary_effect(location);
-                    for local in self.storage_liveness.get().iter() {
+                    self.maybe_storage_live.seek_after_primary_effect(location);
+                    for local in self.maybe_storage_live.get().iter() {
                         if !self.always_live_locals.contains(local) {
                             self.fail(
                                 location,
diff --git a/tests/ui/mir/lint/no-storage.rs b/tests/ui/mir/lint/no-storage.rs
new file mode 100644
index 00000000000..246a0b34e5d
--- /dev/null
+++ b/tests/ui/mir/lint/no-storage.rs
@@ -0,0 +1,30 @@
+// compile-flags: -Zlint-mir --crate-type=lib -Ztreat-err-as-bug
+// failure-status: 101
+// dont-check-compiler-stderr
+// regex-error-pattern: use of local .*, which has no storage here
+#![feature(custom_mir, core_intrinsics)]
+extern crate core;
+use core::intrinsics::mir::*;
+
+#[custom_mir(dialect = "built")]
+pub fn f(a: bool) {
+    mir!(
+        let b: ();
+        {
+            match a { true => bb1, _ => bb2 }
+        }
+        bb1 = {
+            StorageLive(b);
+            Goto(bb3)
+        }
+        bb2 = {
+            Goto(bb3)
+        }
+        bb3 = {
+            b = ();
+            RET = b;
+            StorageDead(b);
+            Return()
+        }
+    )
+}