Auto merge of rust-lang#96965 - oli-obk:flaky_inliner_ice, r=cjgillot

Gracefully handle normalization failures in the prospective inliner cycle detector

Preliminary work for adding the regression test in rust-lang#96950 to our test suite (it was flaky on glacier).

If this PR solves the flakiness on glacier, we can then merge rust-lang#96950

Author: bors

compiler/rustc_mir_transform/src/inline/cycle.rs

@@ -1,5 +1,4 @@
-use rustc_data_structures::fx::{FxHashMap, FxHashSet};
-use rustc_data_structures::sso::SsoHashSet;
+use rustc_data_structures::fx::{FxHashMap, FxHashSet, FxIndexSet};
 use rustc_data_structures::stack::ensure_sufficient_stack;
 use rustc_hir::def_id::{DefId, LocalDefId};
 use rustc_middle::mir::TerminatorKind;
@@ -45,7 +44,10 @@ crate fn mir_callgraph_reachable<'tcx>(
     ) -> bool {
         trace!(%caller);
         for &(callee, substs) in tcx.mir_inliner_callees(caller.def) {
-            let substs = caller.subst_mir_and_normalize_erasing_regions(tcx, param_env, substs);
+            let Ok(substs) = caller.try_subst_mir_and_normalize_erasing_regions(tcx, param_env, substs) else {
+                trace!(?caller, ?param_env, ?substs, "cannot normalize, skipping");
+                continue;
+            };
             let Some(callee) = ty::Instance::resolve(tcx, param_env, callee, substs).unwrap() else {
                 trace!(?callee, "cannot resolve, skipping");
                 continue;
@@ -150,7 +152,7 @@ crate fn mir_inliner_callees<'tcx>(
         // Functions from other crates and MIR shims
         _ => tcx.instance_mir(instance),
     };
-    let mut calls = SsoHashSet::new();
+    let mut calls = FxIndexSet::default();
     for bb_data in body.basic_blocks() {
         let terminator = bb_data.terminator();
         if let TerminatorKind::Call { func, .. } = &terminator.kind {