Do not create new resume block if there isn't one already

Author: nbdd0121

compiler/rustc_mir_transform/src/remove_noop_landing_pads.rs

@@ -6,8 +6,8 @@ use rustc_middle::ty::TyCtxt;
 use rustc_target::spec::PanicStrategy;
 
 /// A pass that removes noop landing pads and replaces jumps to them with
-/// `None`. This is important because otherwise LLVM generates terrible
-/// code for these.
+/// `UnwindAction::Continue`. This is important because otherwise LLVM generates
+/// terrible code for these.
 pub struct RemoveNoopLandingPads;
 
 impl<'tcx> MirPass<'tcx> for RemoveNoopLandingPads {
@@ -84,7 +84,17 @@ impl RemoveNoopLandingPads {
     fn remove_nop_landing_pads(&self, body: &mut Body<'_>) {
         debug!("body: {:#?}", body);
 
-        // make sure there's a resume block
+        // Skip the pass if there are no blocks with a resume terminator.
+        let has_resume = body
+            .basic_blocks
+            .iter_enumerated()
+            .any(|(_bb, block)| matches!(block.terminator().kind, TerminatorKind::Resume));
+        if !has_resume {
+            debug!("remove_noop_landing_pads: no resume block in MIR");
+            return;
+        }
+
+        // make sure there's a resume block without any statements
         let resume_block = {
             let mut patch = MirPatch::new(body);
             let resume_block = patch.resume_block();