Shrink `TyKind::FnPtr`.

By splitting the `FnSig` within `TyKind::FnPtr` into `FnSigTys` and
`FnHeader`, which can be packed more efficiently. This reduces the size
of the hot `TyKind` type from 32 bytes to 24 bytes on 64-bit platforms.
This reduces peak memory usage by a few percent on some benchmarks. It
also reduces cache misses and page faults similarly, though this doesn't
translate to clear cycles or wall-time improvements on CI.

1 files changed, 2 insertions, 2 deletions

diff --git a/compiler/rustc_const_eval/src/interpret/cast.rs b/compiler/rustc_const_eval/src/interpret/cast.rs
index b2f07de0ac4..6a6e7250f33 100644
--- a/compiler/rustc_const_eval/src/interpret/cast.rs
+++ b/compiler/rustc_const_eval/src/interpret/cast.rs
@@ -97,7 +97,7 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
             CastKind::PointerCoercion(PointerCoercion::UnsafeFnPointer) => {
                 let src = self.read_immediate(src)?;
                 match cast_ty.kind() {
-                    ty::FnPtr(_) => {
+                    ty::FnPtr(..) => {
                         // No change to value
                         self.write_immediate(*src, dest)?;
                     }
@@ -230,7 +230,7 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
         src: &ImmTy<'tcx, M::Provenance>,
         cast_to: TyAndLayout<'tcx>,
     ) -> InterpResult<'tcx, ImmTy<'tcx, M::Provenance>> {
-        assert_matches!(src.layout.ty.kind(), ty::RawPtr(_, _) | ty::FnPtr(_));
+        assert_matches!(src.layout.ty.kind(), ty::RawPtr(_, _) | ty::FnPtr(..));
         assert!(cast_to.ty.is_integral());
 
         let scalar = src.to_scalar();