Avoid copying and reconstruction

Author: fee1-dead

compiler/rustc_metadata/src/rmeta/decoder/cstore_impl.rs

@@ -123,8 +123,7 @@ provide! { <'tcx> tcx, def_id, other, cdata,
     thir_abstract_const => { cdata.get_thir_abstract_const(tcx, def_id.index) }
     unused_generic_params => { cdata.get_unused_generic_params(def_id.index) }
     const_param_default => {
-        let c = cdata.get_const_param_default(tcx, def_id.index);
-        tcx.mk_const(c.ty(), c.val())
+        tcx.mk_const_(cdata.get_const_param_default(tcx, def_id.index))
     }
     mir_const_qualif => { cdata.mir_const_qualif(def_id.index) }
     fn_sig => { cdata.fn_sig(def_id.index, tcx) }

compiler/rustc_middle/src/ty/codec.rs

@@ -333,8 +333,7 @@ impl<'tcx, D: TyDecoder<'tcx>> RefDecodable<'tcx, D>
 
 impl<'tcx, D: TyDecoder<'tcx>> RefDecodable<'tcx, D> for ty::Const<'tcx> {
     fn decode(decoder: &mut D) -> Result<&'tcx Self, D::Error> {
-        let c: ty::Const<'_> = Decodable::decode(decoder)?;
-        Ok(decoder.tcx().mk_const(c.ty, c.val))
+        Ok(decoder.tcx().mk_const_(Decodable::decode(decoder)?))
     }
 }
 

compiler/rustc_middle/src/ty/context.rs

@@ -176,8 +176,8 @@ impl<'tcx> CtxtInterners<'tcx> {
     }
 
     #[inline(never)]
-    fn intern_const(&self, ty: Ty<'tcx>, val: ty::ConstKind<'tcx>) -> &'tcx Const<'tcx> {
-        self.const_.intern(CstHash(Const { ty, val }), |c| Interned(self.arena.alloc(c.0))).0
+    fn intern_const(&self, const_: Const<'tcx>) -> &'tcx Const<'tcx> {
+        self.const_.intern(CstHash(const_), |c| Interned(self.arena.alloc(c.0))).0
     }
 }
 
@@ -934,7 +934,7 @@ impl<'tcx> CommonLifetimes<'tcx> {
 
 impl<'tcx> CommonConsts<'tcx> {
     fn new(interners: &CtxtInterners<'tcx>, types: &CommonTypes<'tcx>) -> CommonConsts<'tcx> {
-        let mk_const = |ty, val| interners.intern_const(ty, val);
+        let mk_const = |ty, val| interners.intern_const(ty::Const { ty, val });
 
         CommonConsts {
             unit: mk_const(types.unit, ty::ConstKind::Value(ConstValue::Scalar(Scalar::ZST))),
@@ -2248,7 +2248,13 @@ impl<'tcx> TyCtxt<'tcx> {
 
     #[inline]
     pub fn mk_const(self, ty: Ty<'tcx>, val: ty::ConstKind<'tcx>) -> &'tcx Const<'tcx> {
-        self.interners.intern_const(ty, val)
+        self.interners.intern_const(ty::Const { ty, val })
+    }
+
+    /// Same as `mk_const` but interns a constructed `ty::Const` which one might get from decoding the on-disk cache
+    #[inline]
+    pub fn mk_const_(self, const_: ty::Const<'tcx>) -> &'tcx Const<'tcx> {
+        self.interners.intern_const(const_)
     }
 
     #[inline]