Stop collecting unmentioned constants

This avoids generating useless dead LLVM IR.

1 files changed, 8 insertions, 6 deletions

diff --git a/compiler/rustc_monomorphize/src/collector.rs b/compiler/rustc_monomorphize/src/collector.rs
index 173030e0326..3eb9a9dc850 100644
--- a/compiler/rustc_monomorphize/src/collector.rs
+++ b/compiler/rustc_monomorphize/src/collector.rs
@@ -1481,12 +1481,14 @@ impl<'v> RootCollector<'_, 'v> {
                 // Const items only generate mono items if they are actually used somewhere.
                 // Just declaring them is insufficient.
 
-                // But even just declaring them must collect the items they refer to
-                // unless their generics require monomorphization.
-                if !self.tcx.generics_of(id.owner_id).own_requires_monomorphization()
-                    && let Ok(val) = self.tcx.const_eval_poly(id.owner_id.to_def_id())
-                {
-                    collect_const_value(self.tcx, val, self.output);
+                // If we're collecting items eagerly, then recurse into all constants.
+                // Otherwise the value is only collected when explicitly mentioned in other items.
+                if self.strategy == MonoItemCollectionStrategy::Eager {
+                    if !self.tcx.generics_of(id.owner_id).own_requires_monomorphization()
+                        && let Ok(val) = self.tcx.const_eval_poly(id.owner_id.to_def_id())
+                    {
+                        collect_const_value(self.tcx, val, self.output);
+                    }
                 }
             }
             DefKind::Impl { .. } => {