promote_consts: eargerly return when there are no candidates

There is no need to do it when mustn't.

1 files changed, 5 insertions, 0 deletions

diff --git a/compiler/rustc_mir_transform/src/promote_consts.rs b/compiler/rustc_mir_transform/src/promote_consts.rs
index a0ee4c432c6..2f7d8d96eac 100644
--- a/compiler/rustc_mir_transform/src/promote_consts.rs
+++ b/compiler/rustc_mir_transform/src/promote_consts.rs
@@ -970,6 +970,11 @@ fn promote_candidates<'tcx>(
     // Visit candidates in reverse, in case they're nested.
     debug!(promote_candidates = ?candidates);
 
+    // eagerly fail fast
+    if candidates.is_empty() {
+        return IndexVec::new();
+    }
+
     let mut promotions = IndexVec::new();
 
     let mut extra_statements = vec![];