Force-inline shallow_resolve at its hottest call site.

It's a ~1% win on `keccak` and `inflate`.
rust-lang · bors · Aug 31, 2018 · Aug 6, 2018 · Aug 15, 2018 · Aug 15, 2018
commit b73843f9422fb487b2d26ac2d65f79f73a4c9ae3
diff --git a/src/librustc/infer/mod.rs b/src/librustc/infer/mod.rs
@@ -1116,7 +1116,11 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
         self.resolve_type_vars_if_possible(t).to_string()
     }
 
-    pub fn shallow_resolve(&self, typ: Ty<'tcx>) -> Ty<'tcx> {
+    // We have this force-inlined variant of shallow_resolve() for the one
+    // callsite that is extremely hot. All other callsites use the normal
+    // variant.
+    #[inline(always)]
+    pub fn inlined_shallow_resolve(&self, typ: Ty<'tcx>) -> Ty<'tcx> {
         match typ.sty {
             ty::TyInfer(ty::TyVar(v)) => {
                 // Not entirely obvious: if `typ` is a type variable,
@@ -1157,6 +1161,10 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
         }
     }
 
+    pub fn shallow_resolve(&self, typ: Ty<'tcx>) -> Ty<'tcx> {
+        self.inlined_shallow_resolve(typ)
+    }
+
     pub fn resolve_type_vars_if_possible<T>(&self, value: &T) -> T
         where T: TypeFoldable<'tcx>
     {

diff --git a/src/librustc/traits/fulfill.rs b/src/librustc/traits/fulfill.rs
@@ -269,7 +269,8 @@ impl<'a, 'b, 'gcx, 'tcx> ObligationProcessor for FulfillProcessor<'a, 'b, 'gcx,
         // doing more work yet
         if !pending_obligation.stalled_on.is_empty() {
             if pending_obligation.stalled_on.iter().all(|&ty| {
-                let resolved_ty = self.selcx.infcx().shallow_resolve(&ty);
+                // Use the force-inlined variant of shallow_resolve() because this code is hot.
+                let resolved_ty = self.selcx.infcx().inlined_shallow_resolve(&ty);
                 resolved_ty == ty // nothing changed here
             }) {
                 debug!("process_predicate: pending obligation {:?} still stalled on {:?}",