Test performance impact of removing untracked vtable cache from tcx

compiler/rustc_middle/src/ty/context.rs

@@ -9,7 +9,7 @@ use crate::lint::{struct_lint_level, LintDiagnosticBuilder, LintLevelSource};
 use crate::middle;
 use crate::middle::resolve_lifetime::{self, LifetimeScopeForPath, ObjectLifetimeDefault};
 use crate::middle::stability;
-use crate::mir::interpret::{self, AllocId, Allocation, ConstValue, Scalar};
+use crate::mir::interpret::{self, Allocation, ConstValue, Scalar};
 use crate::mir::{Body, Field, Local, Place, PlaceElem, ProjectionKind, Promoted};
 use crate::thir::Thir;
 use crate::traits;
@@ -1047,10 +1047,6 @@ pub struct GlobalCtxt<'tcx> {
     pub(crate) alloc_map: Lock<interpret::AllocMap<'tcx>>,
 
     output_filenames: Arc<OutputFilenames>,
-
-    // FIXME(eddyb) this doesn't belong here and should be using a query.
-    pub(super) vtables_cache:
-        Lock<FxHashMap<(Ty<'tcx>, Option<ty::PolyExistentialTraitRef<'tcx>>), AllocId>>,
 }
 
 impl<'tcx> TyCtxt<'tcx> {
@@ -1189,7 +1185,6 @@ impl<'tcx> TyCtxt<'tcx> {
             const_stability_interner: Default::default(),
             alloc_map: Lock::new(interpret::AllocMap::new()),
             output_filenames: Arc::new(output_filenames),
-            vtables_cache: Default::default(),
         }
     }
 

compiler/rustc_middle/src/ty/vtable.rs

@@ -52,11 +52,6 @@ impl<'tcx> TyCtxt<'tcx> {
         poly_trait_ref: Option<ty::PolyExistentialTraitRef<'tcx>>,
     ) -> AllocId {
         let tcx = self;
-        let vtables_cache = tcx.vtables_cache.lock();
-        if let Some(alloc_id) = vtables_cache.get(&(ty, poly_trait_ref)).cloned() {
-            return alloc_id;
-        }
-        drop(vtables_cache);
 
         let vtable_entries = if let Some(poly_trait_ref) = poly_trait_ref {
             let trait_ref = poly_trait_ref.with_self_ty(tcx, ty);
@@ -119,9 +114,6 @@ impl<'tcx> TyCtxt<'tcx> {
         }
 
         vtable.mutability = Mutability::Not;
-        let alloc_id = tcx.create_memory_alloc(tcx.intern_const_alloc(vtable));
-        let mut vtables_cache = self.vtables_cache.lock();
-        vtables_cache.insert((ty, poly_trait_ref), alloc_id);
-        alloc_id
+        tcx.create_memory_alloc(tcx.intern_const_alloc(vtable))
     }
 }

src/test/incremental/reorder_vtable.rs

@@ -0,0 +1,27 @@
+// revisions:rpass1 rpass2
+
+trait Foo {
+    #[cfg(rpass1)]
+    fn method1(&self) -> u32;
+
+    fn method2(&self) -> u32;
+
+    #[cfg(rpass2)]
+    fn method1(&self) -> u32;
+}
+
+impl Foo for u32 {
+    fn method1(&self) -> u32 { 17 }
+    fn method2(&self) -> u32 { 42 }
+}
+
+fn main() {
+    let x: &dyn Foo = &0u32;
+    assert_eq!(mod1::foo(x), 17);
+}
+
+mod mod1 {
+    pub fn foo(x: &dyn super::Foo) -> u32 {
+        x.method1()
+    }
+}