Rollup merge of #119252 - Enselic:rustc_mir_transform-query-stability, r=cjgillot

rustc_mir_transform: Enforce `rustc::potential_query_instability` lint

Stop allowing `rustc::potential_query_instability` on all of rustc_mir_transform and instead allow it on a case-by-case basis if it is safe to do so. In this particular crate, all instances were safe to allow.

Part of https://github.com/rust-lang/rust/issues/84447 which is E-help-wanted.

3 files changed, 4 insertions, 1 deletions

diff --git a/compiler/rustc_mir_transform/src/const_prop_lint.rs b/compiler/rustc_mir_transform/src/const_prop_lint.rs
index 99eecb567f2..d0bbca08a40 100644
--- a/compiler/rustc_mir_transform/src/const_prop_lint.rs
+++ b/compiler/rustc_mir_transform/src/const_prop_lint.rs
@@ -670,6 +670,8 @@ impl<'tcx> Visitor<'tcx> for ConstPropagator<'_, 'tcx> {
         // This loop can get very hot for some bodies: it check each local in each bb.
         // To avoid this quadratic behaviour, we only clear the locals that were modified inside
         // the current block.
+        // The order in which we remove consts does not matter.
+        #[allow(rustc::potential_query_instability)]
         for local in written_only_inside_own_block_locals.drain() {
             debug_assert_eq!(
                 self.ecx.machine.can_const_prop[local],
diff --git a/compiler/rustc_mir_transform/src/lib.rs b/compiler/rustc_mir_transform/src/lib.rs
index 164b6b9c4f5..f5f51c0ec8a 100644
--- a/compiler/rustc_mir_transform/src/lib.rs
+++ b/compiler/rustc_mir_transform/src/lib.rs
@@ -1,4 +1,3 @@
-#![allow(rustc::potential_query_instability)]
 #![deny(rustc::untranslatable_diagnostic)]
 #![deny(rustc::diagnostic_outside_of_impl)]
 #![feature(box_patterns)]
diff --git a/compiler/rustc_mir_transform/src/unreachable_prop.rs b/compiler/rustc_mir_transform/src/unreachable_prop.rs
index f12a6aa2429..bff59aa6023 100644
--- a/compiler/rustc_mir_transform/src/unreachable_prop.rs
+++ b/compiler/rustc_mir_transform/src/unreachable_prop.rs
@@ -54,6 +54,8 @@ impl MirPass<'_> for UnreachablePropagation {
         patch.apply(body);
 
         // We do want do keep some unreachable blocks, but make them empty.
+        // The order in which we clear bb statements does not matter.
+        #[allow(rustc::potential_query_instability)]
         for bb in unreachable_blocks {
             body.basic_blocks_mut()[bb].statements.clear();
         }