Auto merge of #132527 - DianQK:gvn-stmt-iter, r=oli-obk

gvn: Invalid dereferences for all non-local mutations

Fixes #132353.

This PR removes the computation value by traversing SSA locals through `for_each_assignment_mut`.

Because the `for_each_assignment_mut` traversal skips statements which have side effects, such as dereference assignments, the computation may be unsound. Instead of `for_each_assignment_mut`, we compute values by traversing in reverse postorder.

Because we compute and use the symbolic representation of values on the fly, I invalidate all old values when encountering a dereference assignment. The current approach does not prevent the optimization of a clone to a copy.

In the future, we may add an alias model, or dominance information for dereference assignments, or SSA form to help GVN.

r? cjgillot

cc `@jieyouxu` #132356
cc `@RalfJung` #133474

Author: bors

compiler/rustc_data_structures/src/fx.rs

@@ -9,6 +9,8 @@ pub type FxIndexSet<V> = indexmap::IndexSet<V, BuildHasherDefault<FxHasher>>;
 pub type IndexEntry<'a, K, V> = indexmap::map::Entry<'a, K, V>;
 pub type IndexOccupiedEntry<'a, K, V> = indexmap::map::OccupiedEntry<'a, K, V>;
 
+pub use indexmap::set::MutableValues;
+
 #[macro_export]
 macro_rules! define_id_collections {
     ($map_name:ident, $set_name:ident, $entry_name:ident, $key:ty) => {