Lower discriminant_value intrinsic
This allows const propagation to evaluate comparisons involving field-less enums using derived implementations of `PartialEq` (after inlining `eq`).
This commit is contained in:
Tomasz Miąsko
parent
d32c320d7e
commit
686237c49a
@ -489,6 +489,7 @@ pub fn codegen_rvalue_operand(
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mir::Rvalue::Discriminant(ref place) => {
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let discr_ty = rvalue.ty(self.mir, bx.tcx());
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let discr_ty = self.monomorphize(discr_ty);
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let discr = self
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.codegen_place(&mut bx, place.as_ref())
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.codegen_get_discr(&mut bx, discr_ty);
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@ -2213,13 +2213,44 @@ pub fn discriminant_for_variant(
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}
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/// Returns the type of the discriminant of this type.
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pub fn discriminant_ty(&self, tcx: TyCtxt<'tcx>) -> Ty<'tcx> {
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pub fn discriminant_ty(&'tcx self, tcx: TyCtxt<'tcx>) -> Ty<'tcx> {
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match self.kind() {
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ty::Adt(adt, _) if adt.is_enum() => adt.repr.discr_type().to_ty(tcx),
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ty::Generator(_, substs, _) => substs.as_generator().discr_ty(tcx),
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_ => {
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// This can only be `0`, for now, so `u8` will suffice.
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tcx.types.u8
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ty::Param(_) | ty::Projection(_) | ty::Opaque(..) | ty::Infer(ty::TyVar(_)) => {
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let assoc_items =
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tcx.associated_items(tcx.lang_items().discriminant_kind_trait().unwrap());
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let discriminant_def_id = assoc_items.in_definition_order().next().unwrap().def_id;
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tcx.mk_projection(discriminant_def_id, tcx.mk_substs([self.into()].iter()))
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}
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ty::Bool
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| ty::Char
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| ty::Int(_)
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| ty::Uint(_)
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| ty::Float(_)
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| ty::Adt(..)
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| ty::Foreign(_)
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| ty::Str
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| ty::Array(..)
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| ty::Slice(_)
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| ty::RawPtr(_)
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| ty::Ref(..)
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| ty::FnDef(..)
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| ty::FnPtr(..)
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| ty::Dynamic(..)
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| ty::Closure(..)
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| ty::GeneratorWitness(..)
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| ty::Never
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| ty::Tuple(_)
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| ty::Error(_)
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| ty::Infer(IntVar(_) | FloatVar(_)) => tcx.types.u8,
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ty::Bound(..)
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| ty::Placeholder(_)
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| ty::Infer(FreshTy(_) | ty::FreshIntTy(_) | ty::FreshFloatTy(_)) => {
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bug!("`discriminant_ty` applied to unexpected type: {:?}", self)
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}
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}
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}
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@ -83,6 +83,21 @@ fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
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terminator.kind = TerminatorKind::Goto { target };
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}
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}
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sym::discriminant_value => {
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if let (Some((destination, target)), Some(arg)) =
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(*destination, args[0].place())
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{
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let arg = tcx.mk_place_deref(arg);
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block.statements.push(Statement {
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source_info: terminator.source_info,
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kind: StatementKind::Assign(box (
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destination,
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Rvalue::Discriminant(arg),
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)),
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});
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terminator.kind = TerminatorKind::Goto { target };
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}
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}
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_ => {}
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}
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}
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@ -0,0 +1,124 @@
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- // MIR for `discriminant` before LowerIntrinsics
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+ // MIR for `discriminant` after LowerIntrinsics
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fn discriminant(_1: T) -> () {
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debug t => _1; // in scope 0 at $DIR/lower_intrinsics.rs:68:24: 68:25
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let mut _0: (); // return place in scope 0 at $DIR/lower_intrinsics.rs:68:30: 68:30
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let _2: <T as std::marker::DiscriminantKind>::Discriminant; // in scope 0 at $DIR/lower_intrinsics.rs:69:5: 69:45
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let mut _3: &T; // in scope 0 at $DIR/lower_intrinsics.rs:69:42: 69:44
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let _4: &T; // in scope 0 at $DIR/lower_intrinsics.rs:69:42: 69:44
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let _5: u8; // in scope 0 at $DIR/lower_intrinsics.rs:70:5: 70:45
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let mut _6: &i32; // in scope 0 at $DIR/lower_intrinsics.rs:70:42: 70:44
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let _7: &i32; // in scope 0 at $DIR/lower_intrinsics.rs:70:42: 70:44
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let _8: i32; // in scope 0 at $DIR/lower_intrinsics.rs:70:43: 70:44
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let _9: u8; // in scope 0 at $DIR/lower_intrinsics.rs:71:5: 71:46
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let mut _10: &(); // in scope 0 at $DIR/lower_intrinsics.rs:71:42: 71:45
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let _11: &(); // in scope 0 at $DIR/lower_intrinsics.rs:71:42: 71:45
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let _12: (); // in scope 0 at $DIR/lower_intrinsics.rs:71:43: 71:45
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let _13: isize; // in scope 0 at $DIR/lower_intrinsics.rs:72:5: 72:48
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let mut _14: &E; // in scope 0 at $DIR/lower_intrinsics.rs:72:42: 72:47
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let _15: &E; // in scope 0 at $DIR/lower_intrinsics.rs:72:42: 72:47
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let _16: E; // in scope 0 at $DIR/lower_intrinsics.rs:72:43: 72:47
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let mut _17: &E; // in scope 0 at $DIR/lower_intrinsics.rs:72:42: 72:47
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let mut _18: &(); // in scope 0 at $DIR/lower_intrinsics.rs:71:42: 71:45
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let mut _19: &i32; // in scope 0 at $DIR/lower_intrinsics.rs:70:42: 70:44
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bb0: {
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StorageLive(_2); // scope 0 at $DIR/lower_intrinsics.rs:69:5: 69:45
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StorageLive(_3); // scope 0 at $DIR/lower_intrinsics.rs:69:42: 69:44
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StorageLive(_4); // scope 0 at $DIR/lower_intrinsics.rs:69:42: 69:44
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_4 = &_1; // scope 0 at $DIR/lower_intrinsics.rs:69:42: 69:44
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_3 = &(*_4); // scope 0 at $DIR/lower_intrinsics.rs:69:42: 69:44
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- _2 = discriminant_value::<T>(move _3) -> bb1; // scope 0 at $DIR/lower_intrinsics.rs:69:5: 69:45
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- // mir::Constant
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- // + span: $DIR/lower_intrinsics.rs:69:5: 69:41
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- // + literal: Const { ty: for<'r> extern "rust-intrinsic" fn(&'r T) -> <T as std::marker::DiscriminantKind>::Discriminant {std::intrinsics::discriminant_value::<T>}, val: Value(Scalar(<ZST>)) }
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+ _2 = discriminant((*_3)); // scope 0 at $DIR/lower_intrinsics.rs:69:5: 69:45
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+ goto -> bb1; // scope 0 at $DIR/lower_intrinsics.rs:69:5: 69:45
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}
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bb1: {
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StorageDead(_3); // scope 0 at $DIR/lower_intrinsics.rs:69:44: 69:45
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StorageDead(_4); // scope 0 at $DIR/lower_intrinsics.rs:69:45: 69:46
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StorageDead(_2); // scope 0 at $DIR/lower_intrinsics.rs:69:45: 69:46
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StorageLive(_5); // scope 0 at $DIR/lower_intrinsics.rs:70:5: 70:45
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StorageLive(_6); // scope 0 at $DIR/lower_intrinsics.rs:70:42: 70:44
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StorageLive(_7); // scope 0 at $DIR/lower_intrinsics.rs:70:42: 70:44
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_19 = const discriminant::<T>::promoted[2]; // scope 0 at $DIR/lower_intrinsics.rs:70:42: 70:44
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// ty::Const
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// + ty: &i32
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// + val: Unevaluated(WithOptConstParam { did: DefId(0:27 ~ lower_intrinsics[8787]::discriminant), const_param_did: None }, [T], Some(promoted[2]))
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// mir::Constant
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// + span: $DIR/lower_intrinsics.rs:70:42: 70:44
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// + literal: Const { ty: &i32, val: Unevaluated(WithOptConstParam { did: DefId(0:27 ~ lower_intrinsics[8787]::discriminant), const_param_did: None }, [T], Some(promoted[2])) }
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_7 = &(*_19); // scope 0 at $DIR/lower_intrinsics.rs:70:42: 70:44
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_6 = &(*_7); // scope 0 at $DIR/lower_intrinsics.rs:70:42: 70:44
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- _5 = discriminant_value::<i32>(move _6) -> bb2; // scope 0 at $DIR/lower_intrinsics.rs:70:5: 70:45
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- // mir::Constant
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- // + span: $DIR/lower_intrinsics.rs:70:5: 70:41
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- // + literal: Const { ty: for<'r> extern "rust-intrinsic" fn(&'r i32) -> <i32 as std::marker::DiscriminantKind>::Discriminant {std::intrinsics::discriminant_value::<i32>}, val: Value(Scalar(<ZST>)) }
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+ _5 = discriminant((*_6)); // scope 0 at $DIR/lower_intrinsics.rs:70:5: 70:45
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+ goto -> bb2; // scope 0 at $DIR/lower_intrinsics.rs:70:5: 70:45
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}
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bb2: {
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StorageDead(_6); // scope 0 at $DIR/lower_intrinsics.rs:70:44: 70:45
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StorageDead(_7); // scope 0 at $DIR/lower_intrinsics.rs:70:45: 70:46
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StorageDead(_5); // scope 0 at $DIR/lower_intrinsics.rs:70:45: 70:46
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StorageLive(_9); // scope 0 at $DIR/lower_intrinsics.rs:71:5: 71:46
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StorageLive(_10); // scope 0 at $DIR/lower_intrinsics.rs:71:42: 71:45
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StorageLive(_11); // scope 0 at $DIR/lower_intrinsics.rs:71:42: 71:45
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_18 = const discriminant::<T>::promoted[1]; // scope 0 at $DIR/lower_intrinsics.rs:71:42: 71:45
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// ty::Const
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// + ty: &()
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// + val: Unevaluated(WithOptConstParam { did: DefId(0:27 ~ lower_intrinsics[8787]::discriminant), const_param_did: None }, [T], Some(promoted[1]))
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// mir::Constant
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// + span: $DIR/lower_intrinsics.rs:71:42: 71:45
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// + literal: Const { ty: &(), val: Unevaluated(WithOptConstParam { did: DefId(0:27 ~ lower_intrinsics[8787]::discriminant), const_param_did: None }, [T], Some(promoted[1])) }
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_11 = &(*_18); // scope 0 at $DIR/lower_intrinsics.rs:71:42: 71:45
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_10 = &(*_11); // scope 0 at $DIR/lower_intrinsics.rs:71:42: 71:45
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- _9 = discriminant_value::<()>(move _10) -> bb3; // scope 0 at $DIR/lower_intrinsics.rs:71:5: 71:46
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- // mir::Constant
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- // + span: $DIR/lower_intrinsics.rs:71:5: 71:41
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- // + literal: Const { ty: for<'r> extern "rust-intrinsic" fn(&'r ()) -> <() as std::marker::DiscriminantKind>::Discriminant {std::intrinsics::discriminant_value::<()>}, val: Value(Scalar(<ZST>)) }
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+ _9 = discriminant((*_10)); // scope 0 at $DIR/lower_intrinsics.rs:71:5: 71:46
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+ goto -> bb3; // scope 0 at $DIR/lower_intrinsics.rs:71:5: 71:46
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}
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bb3: {
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StorageDead(_10); // scope 0 at $DIR/lower_intrinsics.rs:71:45: 71:46
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StorageDead(_11); // scope 0 at $DIR/lower_intrinsics.rs:71:46: 71:47
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StorageDead(_9); // scope 0 at $DIR/lower_intrinsics.rs:71:46: 71:47
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StorageLive(_13); // scope 0 at $DIR/lower_intrinsics.rs:72:5: 72:48
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StorageLive(_14); // scope 0 at $DIR/lower_intrinsics.rs:72:42: 72:47
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StorageLive(_15); // scope 0 at $DIR/lower_intrinsics.rs:72:42: 72:47
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_17 = const discriminant::<T>::promoted[0]; // scope 0 at $DIR/lower_intrinsics.rs:72:42: 72:47
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// ty::Const
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// + ty: &E
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// + val: Unevaluated(WithOptConstParam { did: DefId(0:27 ~ lower_intrinsics[8787]::discriminant), const_param_did: None }, [T], Some(promoted[0]))
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// mir::Constant
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// + span: $DIR/lower_intrinsics.rs:72:42: 72:47
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// + literal: Const { ty: &E, val: Unevaluated(WithOptConstParam { did: DefId(0:27 ~ lower_intrinsics[8787]::discriminant), const_param_did: None }, [T], Some(promoted[0])) }
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_15 = &(*_17); // scope 0 at $DIR/lower_intrinsics.rs:72:42: 72:47
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_14 = &(*_15); // scope 0 at $DIR/lower_intrinsics.rs:72:42: 72:47
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- _13 = discriminant_value::<E>(move _14) -> bb4; // scope 0 at $DIR/lower_intrinsics.rs:72:5: 72:48
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- // mir::Constant
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- // + span: $DIR/lower_intrinsics.rs:72:5: 72:41
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- // + literal: Const { ty: for<'r> extern "rust-intrinsic" fn(&'r E) -> <E as std::marker::DiscriminantKind>::Discriminant {std::intrinsics::discriminant_value::<E>}, val: Value(Scalar(<ZST>)) }
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+ _13 = discriminant((*_14)); // scope 0 at $DIR/lower_intrinsics.rs:72:5: 72:48
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+ goto -> bb4; // scope 0 at $DIR/lower_intrinsics.rs:72:5: 72:48
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}
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bb4: {
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StorageDead(_14); // scope 0 at $DIR/lower_intrinsics.rs:72:47: 72:48
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StorageDead(_15); // scope 0 at $DIR/lower_intrinsics.rs:72:48: 72:49
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StorageDead(_13); // scope 0 at $DIR/lower_intrinsics.rs:72:48: 72:49
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_0 = const (); // scope 0 at $DIR/lower_intrinsics.rs:68:30: 73:2
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drop(_1) -> bb5; // scope 0 at $DIR/lower_intrinsics.rs:73:1: 73:2
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}
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bb5: {
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return; // scope 0 at $DIR/lower_intrinsics.rs:73:2: 73:2
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}
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}
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@ -45,11 +45,11 @@ pub fn f_dispatch<T>(t: T) {
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}
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#[inline(never)]
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pub fn f_zst<T>(t: T) {
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pub fn f_zst<T>(_t: T) {
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}
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#[inline(never)]
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pub fn f_non_zst<T>(t: T) {}
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pub fn f_non_zst<T>(_t: T) {}
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// EMIT_MIR lower_intrinsics.non_const.LowerIntrinsics.diff
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pub fn non_const<T>() -> usize {
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@ -57,3 +57,17 @@ pub fn non_const<T>() -> usize {
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let size_of_t = core::intrinsics::size_of::<T>;
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size_of_t()
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}
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pub enum E {
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A,
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B,
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C,
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}
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// EMIT_MIR lower_intrinsics.discriminant.LowerIntrinsics.diff
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pub fn discriminant<T>(t: T) {
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core::intrinsics::discriminant_value(&t);
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core::intrinsics::discriminant_value(&0);
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core::intrinsics::discriminant_value(&());
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core::intrinsics::discriminant_value(&E::B);
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}
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