Keep inline(always) in multiple CGUs

compiler/rustc_middle/src/mir/mono.rs

@@ -1,5 +1,6 @@
 use crate::dep_graph::{DepNode, WorkProduct, WorkProductId};
 use crate::ty::{GenericArgs, Instance, InstanceDef, SymbolName, TyCtxt};
+use rustc_attr::InlineAttr;
 use rustc_data_structures::base_n;
 use rustc_data_structures::fingerprint::Fingerprint;
 use rustc_data_structures::fx::FxHashMap;
@@ -117,7 +118,15 @@ impl<'tcx> MonoItem<'tcx> {
                     return InstantiationMode::LocalCopy;
                 }
 
-                return InstantiationMode::GloballyShared { may_conflict: true };
+                // Finally, if this is `#[inline(always)]` we're sure to respect
+                // that with an inline copy per CGU, but otherwise we'll be
+                // creating one copy of this `#[inline]` function which may
+                // conflict with upstream crates as it could be an exported
+                // symbol.
+                match tcx.codegen_fn_attrs(instance.def_id()).inline {
+                    InlineAttr::Always => InstantiationMode::LocalCopy,
+                    _ => InstantiationMode::GloballyShared { may_conflict: true },
+                }
             }
             MonoItem::Static(..) | MonoItem::GlobalAsm(..) => {
                 InstantiationMode::GloballyShared { may_conflict: false }