normalize substs during inlining

compiler/rustc_mir/src/transform/inline.rs

@@ -201,9 +201,13 @@ impl Inliner<'tcx> {
         let terminator = bb_data.terminator();
         if let TerminatorKind::Call { func: ref op, .. } = terminator.kind {
             if let ty::FnDef(callee_def_id, substs) = *op.ty(caller_body, self.tcx).kind() {
-                let instance = Instance::resolve(self.tcx, self.param_env, callee_def_id, substs)
-                    .ok()
-                    .flatten()?;
+                // To resolve an instance its substs have to be fully normalized, so
+                // we do this here.
+                let normalized_substs = self.tcx.normalize_erasing_regions(self.param_env, substs);
+                let instance =
+                    Instance::resolve(self.tcx, self.param_env, callee_def_id, normalized_substs)
+                        .ok()
+                        .flatten()?;
 
                 if let InstanceDef::Virtual(..) = instance.def {
                     return None;

compiler/rustc_trait_selection/src/traits/codegen/mod.rs

@@ -17,14 +17,17 @@ use rustc_middle::ty::{self, TyCtxt};
 /// (necessarily) resolve all nested obligations on the impl. Note
 /// that type check should guarantee to us that all nested
 /// obligations *could be* resolved if we wanted to.
+///
 /// Assumes that this is run after the entire crate has been successfully type-checked.
+/// This also expects that `trait_ref` is fully normalized.
 pub fn codegen_fulfill_obligation<'tcx>(
     tcx: TyCtxt<'tcx>,
     (param_env, trait_ref): (ty::ParamEnv<'tcx>, ty::PolyTraitRef<'tcx>),
 ) -> Result<ImplSource<'tcx, ()>, ErrorReported> {
-    // Remove any references to regions and normalize; this helps improve caching.
-    let trait_ref = tcx.normalize_erasing_regions(param_env, trait_ref);
-
+    // Remove any references to regions; this helps improve caching.
+    let trait_ref = tcx.erase_regions(&trait_ref);
+    // We expect the input to be fully normalized.
+    debug_assert_eq!(trait_ref, tcx.normalize_erasing_regions(param_env, trait_ref));
     debug!(
         "codegen_fulfill_obligation(trait_ref={:?}, def_id={:?})",
         (param_env, trait_ref),

src/test/ui/mir/mir-inlining/ice-issue-77306.rs

@@ -0,0 +1,17 @@
+// run-pass
+// compile-flags:-Zmir-opt-level=2
+
+// Previously ICEd because we did not normalize during inlining,
+// see https://github.com/rust-lang/rust/pull/77306 for more discussion.
+
+pub fn write() {
+    create()()
+}
+
+pub fn create() -> impl FnOnce() {
+   || ()
+}
+
+fn main() {
+    write();
+}