Simplify implementation for perf

compiler/rustc_lint/src/redundant_lifetime_args.rs

@@ -5,11 +5,10 @@ use rustc_data_structures::fx::FxHashSet;
 use rustc_hir as hir;
 use rustc_hir::def::DefKind;
 use rustc_infer::infer::outlives::env::OutlivesEnvironment;
-use rustc_infer::infer::{SubregionOrigin, TyCtxtInferExt};
+use rustc_infer::infer::TyCtxtInferExt;
 use rustc_macros::LintDiagnostic;
 use rustc_middle::ty::{self, TyCtxt};
 use rustc_session::lint::builtin::UNUSED_LIFETIMES;
-use rustc_span::DUMMY_SP;
 use rustc_trait_selection::traits::{outlives_bounds::InferCtxtExt, ObligationCtxt};
 
 use crate::{LateContext, LateLintPass};
@@ -80,17 +79,6 @@ fn check<'tcx>(tcx: TyCtxt<'tcx>, param_env: ty::ParamEnv<'tcx>, owner_id: hir::
         | DefKind::Closure => return,
     }
 
-    let infcx = &tcx.infer_ctxt().build();
-    let ocx = ObligationCtxt::new(infcx);
-
-    // Compute the implied outlives bounds for the item. This ensures that we treat
-    // a signature with an argument like `&'a &'b ()` as implicitly having `'b: 'a`.
-    let Ok(assumed_wf_types) = ocx.assumed_wf_types(param_env, owner_id.def_id) else {
-        return;
-    };
-    let implied_bounds = infcx.implied_bounds_tys(param_env, owner_id.def_id, assumed_wf_types);
-    let outlives_env = &OutlivesEnvironment::with_bounds(param_env, implied_bounds);
-
     // The ordering of this lifetime map is a bit subtle.
     //
     // Specifically, we want to find a "candidate" lifetime that precedes a "victim" lifetime,
@@ -111,6 +99,22 @@ fn check<'tcx>(tcx: TyCtxt<'tcx>, param_env: ty::ParamEnv<'tcx>, owner_id: hir::
         }
     }
 
+    // No lifetimes except for `'static` to check.
+    if lifetimes.len() == 1 {
+        return;
+    }
+
+    let infcx = &tcx.infer_ctxt().build();
+    let ocx = ObligationCtxt::new(infcx);
+
+    // Compute the implied outlives bounds for the item. This ensures that we treat
+    // a signature with an argument like `&'a &'b ()` as implicitly having `'b: 'a`.
+    let Ok(assumed_wf_types) = ocx.assumed_wf_types(param_env, owner_id.def_id) else {
+        return;
+    };
+    let implied_bounds = infcx.implied_bounds_tys(param_env, owner_id.def_id, assumed_wf_types);
+    let outlives_env = &OutlivesEnvironment::with_bounds(param_env, implied_bounds);
+
     // Keep track of lifetimes which have already been replaced with other lifetimes.
     // This makes sure that if `'a = 'b = 'c`, we don't say `'c` should be replaced by
     // both `'a` and `'b`.
@@ -128,6 +132,11 @@ fn check<'tcx>(tcx: TyCtxt<'tcx>, param_env: ty::ParamEnv<'tcx>, owner_id: hir::
         }
 
         for &victim in &lifetimes[(idx + 1)..] {
+            // We should not suggest renaming `'_` in `&'static &'_ str`.
+            if !victim.has_name() {
+                continue;
+            }
+
             // We only care about lifetimes that are "real", i.e. that have a def-id.
             let (ty::ReEarlyParam(ty::EarlyParamRegion { def_id, .. })
             | ty::ReLateParam(ty::LateParamRegion {
@@ -146,14 +155,10 @@ fn check<'tcx>(tcx: TyCtxt<'tcx>, param_env: ty::ParamEnv<'tcx>, owner_id: hir::
                 continue;
             }
 
-            let infcx = infcx.fork();
-
-            // Require that `'candidate = 'victim`
-            infcx.sub_regions(SubregionOrigin::RelateRegionParamBound(DUMMY_SP), candidate, victim);
-            infcx.sub_regions(SubregionOrigin::RelateRegionParamBound(DUMMY_SP), victim, candidate);
-
             // If there are no lifetime errors, then we have proven that `'candidate = 'victim`!
-            if infcx.resolve_regions(outlives_env).is_empty() {
+            if outlives_env.free_region_map().sub_free_regions(tcx, candidate, victim)
+                && outlives_env.free_region_map().sub_free_regions(tcx, victim, candidate)
+            {
                 shadowed.insert(victim);
                 tcx.emit_spanned_lint(
                     UNUSED_LIFETIMES,

tests/ui/regions/transitively-redundant-lifetimes.rs

@@ -13,4 +13,6 @@ impl<'a> Bar<'a> {
     fn d<'b: 'a>(&'b self) {} //~ ERROR unnecessary lifetime parameter `'b`
 }
 
+fn ok(x: &'static &()) {}
+
 fn main() {}