Auto merge of #148066 - lcnr:remove-perf-hack, r=BoxyUwU

remove a performance hack
This hack seems no longer used 🤔 nalgebra compiles without it.
Let's run perf to see whether it matters.
r? `@BoxyUwU`

Author: bors

compiler/rustc_next_trait_solver/src/solve/eval_ctxt/mod.rs

@@ -1308,36 +1308,6 @@ where
 },
 );
 
-// HACK: We bail with overflow if the response would have too many non-region
-// inference variables. This tends to only happen if we encounter a lot of
-// ambiguous alias types which get replaced with fresh inference variables
-// during generalization. This prevents hangs caused by an exponential blowup,
-// see tests/ui/traits/next-solver/coherence-alias-hang.rs.
-matchself.current_goal_kind{
-// We don't do so for `NormalizesTo` goals as we erased the expected term and
-// bailing with overflow here would prevent us from detecting a type-mismatch,
-// causing a coherence error in diesel, see #131969. We still bail with overflow
-// when later returning from the parent AliasRelate goal.
-CurrentGoalKind::NormalizesTo => {}
-CurrentGoalKind::Misc | CurrentGoalKind::CoinductiveTrait => {
-let num_non_region_vars = canonical
-.variables
-.iter()
-.filter(|c| !c.is_region() && c.is_existential())
-.count();
-if num_non_region_vars > self.cx().recursion_limit(){
-debug!(?num_non_region_vars,"too many inference variables -> overflow");
-returnOk(self.make_ambiguous_response_no_constraints(
-MaybeCause::Overflow{
-suggest_increasing_limit:true,
-keep_constraints:false,
-},
-OpaqueTypesJank::AllGood,
-));
-}
-}
-}
-
 Ok(canonical)
 }
 

tests/ui/traits/next-solver/cycles/coinduction/fixpoint-exponential-growth.stderr

@@ -4,7 +4,6 @@ error[E0275]: overflow evaluating the requirement `W<_>: Trait`
 LL | impls::<W<_>>();
  | ^^^^
  |
- = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`fixpoint_exponential_growth`)
 note: required by a bound in `impls`
  --> $DIR/fixpoint-exponential-growth.rs:30:13
  |