Revert "Rollup merge of #149147 - chenyukang:yukang-fix-unused_assignments-macro-gen-147648, r=JonathanBrouwer"

This reverts commit 82a17b30d8, reversing
changes made to 5019bdaefe.

(cherry picked from commit 74387157c7)

compiler/rustc_mir_transform/src/liveness.rs

@@ -75,11 +75,6 @@ pub(crate) fn check_liveness<'tcx>(tcx: TyCtxt<'tcx>, def_id: LocalDefId) -> Den
         return DenseBitSet::new_empty(0);
     }
 
-    // Don't run unused pass for items generated by foreign macros
-    if tcx.def_span(parent).in_external_macro(tcx.sess.source_map()) {
-        return DenseBitSet::new_empty(0);
-    }
-
     let mut body = &*tcx.mir_promoted(def_id).0.borrow();
     let mut body_mem;
 

tests/ui/liveness/auxiliary/aux_issue_147648.rs

@@ -1,7 +0,0 @@
-#[macro_export]
-macro_rules! unused_assign {
-    ($x:ident) => {
-        let mut $x = 1;
-        $x = 2;
-    };
-}

tests/ui/liveness/unused-assignments-from-macro-147648.rs

@@ -1,10 +0,0 @@
-//@ check-pass
-//@ aux-build:aux_issue_147648.rs
-
-#![deny(unused_assignments)]
-
-extern crate aux_issue_147648;
-
-fn main() {
-    aux_issue_147648::unused_assign!(y);
-}