From b8523fd0ec19a70e9d02954d1e6e3145746b63d7 Mon Sep 17 00:00:00 2001
From: Ben Lewis <benlewisj@gmail.com>
Date: Sat, 25 Jan 2020 12:32:58 +1300
Subject: [PATCH] Erase regions before before performing const eval, to improve
 caching.

---
 src/librustc/mir/interpret/queries.rs      | 36 ++++++++++------------
 src/librustc/query/mod.rs                  |  2 +-
 src/librustc_mir/interpret/eval_context.rs |  6 +---
 3 files changed, 19 insertions(+), 25 deletions(-)

diff --git a/src/librustc/mir/interpret/queries.rs b/src/librustc/mir/interpret/queries.rs
index ed57f81e7821..46bf1d969579 100644
--- a/src/librustc/mir/interpret/queries.rs
+++ b/src/librustc/mir/interpret/queries.rs
@@ -13,13 +13,13 @@ impl<'tcx> TyCtxt<'tcx> {
     pub fn const_eval_poly(self, def_id: DefId) -> ConstEvalResult<'tcx> {
         // In some situations def_id will have substitutions within scope, but they aren't allowed
         // to be used. So we can't use `Instance::mono`, instead we feed unresolved substitutions
-        // into `const_eval` which will return `ErrorHandled::ToGeneric` if any og them are
+        // into `const_eval` which will return `ErrorHandled::ToGeneric` if any of them are
         // encountered.
         let substs = InternalSubsts::identity_for_item(self, def_id);
         let instance = ty::Instance::new(def_id, substs);
         let cid = GlobalId { instance, promoted: None };
         let param_env = self.param_env(def_id).with_reveal_all();
-        self.const_eval_validated(param_env.and(cid))
+        self.const_eval_global_id(param_env, cid, None)
     }
 
     /// Resolves and evaluates a constant.
@@ -41,11 +41,8 @@ impl<'tcx> TyCtxt<'tcx> {
     ) -> ConstEvalResult<'tcx> {
         let instance = ty::Instance::resolve(self, param_env, def_id, substs);
         if let Some(instance) = instance {
-            if let Some(promoted) = promoted {
-                self.const_eval_promoted(param_env, instance, promoted)
-            } else {
-                self.const_eval_instance(param_env, instance, span)
-            }
+            let cid = GlobalId { instance, promoted };
+            self.const_eval_global_id(param_env, cid, span)
         } else {
             Err(ErrorHandled::TooGeneric)
         }
@@ -57,22 +54,23 @@ impl<'tcx> TyCtxt<'tcx> {
         instance: ty::Instance<'tcx>,
         span: Option<Span>,
     ) -> ConstEvalResult<'tcx> {
-        let cid = GlobalId { instance, promoted: None };
-        if let Some(span) = span {
-            self.at(span).const_eval_validated(param_env.and(cid))
-        } else {
-            self.const_eval_validated(param_env.and(cid))
-        }
+        self.const_eval_global_id(param_env, GlobalId { instance, promoted: None }, span)
     }
 
-    /// Evaluate a promoted constant.
-    pub fn const_eval_promoted(
+    /// Evaluate a constant.
+    pub fn const_eval_global_id(
         self,
         param_env: ty::ParamEnv<'tcx>,
-        instance: ty::Instance<'tcx>,
-        promoted: mir::Promoted,
+        cid: GlobalId<'tcx>,
+        span: Option<Span>,
     ) -> ConstEvalResult<'tcx> {
-        let cid = GlobalId { instance, promoted: Some(promoted) };
-        self.const_eval_validated(param_env.and(cid))
+        // Const-eval shouldn't depend on lifetimes at all, so we can erase them, which should
+        // improve caching of queries.
+        let inputs = self.erase_regions(&param_env.and(cid));
+        if let Some(span) = span {
+            self.at(span).const_eval_validated(inputs)
+        } else {
+            self.const_eval_validated(inputs)
+        }
     }
 }
diff --git a/src/librustc/query/mod.rs b/src/librustc/query/mod.rs
index 45ab3fc0b85a..e119c214f337 100644
--- a/src/librustc/query/mod.rs
+++ b/src/librustc/query/mod.rs
@@ -502,7 +502,7 @@ rustc_queries! {
         /// returns a proper constant that is usable by the rest of the compiler.
         ///
         /// **Do not use this** directly, use one of the following wrappers: `tcx.const_eval_poly`,
-        /// `tcx.const_eval_resolve`, `tcx.const_eval_instance`, or `tcx.const_eval_promoted`.
+        /// `tcx.const_eval_resolve`, `tcx.const_eval_instance`, or `tcx.const_eval_global_id`.
         query const_eval_validated(key: ty::ParamEnvAnd<'tcx, GlobalId<'tcx>>)
             -> ConstEvalResult<'tcx> {
             no_force
diff --git a/src/librustc_mir/interpret/eval_context.rs b/src/librustc_mir/interpret/eval_context.rs
index fc4ba4d6cd97..cce4b90e224e 100644
--- a/src/librustc_mir/interpret/eval_context.rs
+++ b/src/librustc_mir/interpret/eval_context.rs
@@ -768,11 +768,7 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
         } else {
             self.param_env
         };
-        let val = if let Some(promoted) = gid.promoted {
-            self.tcx.const_eval_promoted(param_env, gid.instance, promoted)?
-        } else {
-            self.tcx.const_eval_instance(param_env, gid.instance, Some(self.tcx.span))?
-        };
+        let val = self.tcx.const_eval_global_id(param_env, gid, Some(self.tcx.span))?;
 
         // Even though `ecx.const_eval` is called from `eval_const_to_op` we can never have a
         // recursion deeper than one level, because the `tcx.const_eval` above is guaranteed to not