Revert "Normalize function type during validation"

This reverts commit d486bfc.

compiler/rustc_mir/src/transform/validate.rs

@@ -364,9 +364,7 @@ impl<'a, 'tcx> Visitor<'tcx> for TypeChecker<'a, 'tcx> {
                 }
             }
             TerminatorKind::Call { func, args, destination, cleanup, .. } => {
-                let param_env = self.param_env.with_reveal_all_normalized(self.tcx);
                 let func_ty = func.ty(&self.body.local_decls, self.tcx);
-                let func_ty = self.tcx.normalize_erasing_regions(param_env, func_ty);
                 match func_ty.kind() {
                     ty::FnPtr(..) | ty::FnDef(..) => {}
                     _ => self.fail(

src/test/ui/issues/issue-50865-private-impl-trait/auxiliary/lib.rs

@@ -1,3 +1,7 @@
+// revisions: default miropt
+//[miropt]compile-flags: -Z mir-opt-level=2
+// ~^ This flag is for #77668, it used to be ICE.
+
 #![crate_type = "lib"]
 
 pub fn bar<P>( // Error won't happen if "bar" is not generic

src/test/ui/mir/mir-inlining/ice-issue-77306-1.rs

@@ -1,27 +1,17 @@
-// Regression test for various issues related to normalization & inlining.
-// * #68347, #77306, #77668 - missed normalization during inlining.
-// * #78442 - missed normalization in validator after inlining.
-//
-// build-pass
+// 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 write_generic<T>(_t: T) {
-    hide()();
-}
-
 pub fn create() -> impl FnOnce() {
    || ()
 }
 
-pub fn hide() -> impl Fn() {
-    write
-}
-
 fn main() {
     write();
-    write_generic(());
 }