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Minimal implementation of implicit deref patterns
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8 files changed

+174
-0
lines changed

8 files changed

+174
-0
lines changed

‎compiler/rustc_hir/src/lang_items.rs‎

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@@ -302,6 +302,8 @@ language_item_table! {
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Range, sym::Range, range_struct, Target::Struct, GenericRequirement::None;
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RangeToInclusive, sym::RangeToInclusive, range_to_inclusive_struct, Target::Struct, GenericRequirement::None;
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RangeTo, sym::RangeTo, range_to_struct, Target::Struct, GenericRequirement::None;
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String, sym::String, string, Target::Struct, GenericRequirement::None;
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}
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pub enum GenericRequirement {

‎compiler/rustc_hir_typeck/src/pat.rs‎

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@@ -401,6 +401,16 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
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}
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}
403403

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if let hir::ExprKind::Lit(Spanned { node: ast::LitKind::Str(..), .. }) = lt.kind {
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let tcx = self.tcx;
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let expected = self.resolve_vars_if_possible(expected);
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pat_ty = match expected.kind() {
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ty::Adt(def, _) if Some(def.did()) == tcx.lang_items().string() => expected,
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ty::Str => tcx.mk_static_str(),
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_ => pat_ty,
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};
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}
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// Somewhat surprising: in this case, the subtyping relation goes the
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// opposite way as the other cases. Actually what we really want is not
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// a subtyping relation at all but rather that there exists a LUB

‎compiler/rustc_mir_build/src/build/matches/test.rs‎

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@@ -240,6 +240,39 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
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}
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TestKind::Eq { value, ty } => {
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let tcx = self.tcx;
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if let ty::Adt(def, _) = ty.kind() && Some(def.did()) == tcx.lang_items().string() {
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if !tcx.features().deref_patterns {
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bug!("matching on `String` went through without enabling deref_patterns");
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}
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let re_erased = tcx.lifetimes.re_erased;
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let ref_string = self.temp(tcx.mk_imm_ref(re_erased, ty), test.span);
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let ref_str_ty = tcx.mk_imm_ref(re_erased, tcx.types.str_);
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let ref_str = self.temp(ref_str_ty, test.span);
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let deref = tcx.require_lang_item(LangItem::Deref, None);
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let method = trait_method(tcx, deref, sym::deref, ty, &[]);
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let eq_block = self.cfg.start_new_block();
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self.cfg.push_assign(block, source_info, ref_string, Rvalue::Ref(re_erased, BorrowKind::Shared, place));
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self.cfg.terminate(
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block,
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source_info,
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TerminatorKind::Call {
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func: Operand::Constant(Box::new(Constant {
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span: test.span,
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user_ty: None,
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literal: method,
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})),
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args: vec![Operand::Move(ref_string)],
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destination: ref_str,
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target: Some(eq_block),
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cleanup: None,
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from_hir_call: false,
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fn_span: source_info.span
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}
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);
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self.non_scalar_compare(eq_block, make_target_blocks, source_info, value, ref_str, ref_str_ty);
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return;
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}
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if !ty.is_scalar() {
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// Use `PartialEq::eq` instead of `BinOp::Eq`
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// (the binop can only handle primitives)

‎library/alloc/src/string.rs‎

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Original file line numberDiff line numberDiff line change
@@ -364,6 +364,7 @@ use crate::vec::Vec;
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#[derive(PartialOrd, Eq, Ord)]
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#[cfg_attr(not(test), rustc_diagnostic_item = "String")]
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#[stable(feature = "rust1", since = "1.0.0")]
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#[cfg_attr(not(bootstrap), lang = "String")]
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pub struct String {
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vec: Vec<u8>,
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}

‎src/test/ui/deref-patterns/basic.rs‎

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@@ -0,0 +1,16 @@
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// run-pass
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// check-run-results
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fn main() {
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test(Some(String::from("42")));
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test(Some(String::new()));
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test(None);
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}
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fn test(o: Option<String>) {
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match o {
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Some("42") => println!("the answer"),
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Some(_) => println!("something else?"),
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None => println!("nil"),
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}
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}

‎src/test/ui/deref-patterns/basic.run.stdout‎

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@@ -0,0 +1,3 @@
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the answer
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something else?
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nil

‎src/test/ui/deref-patterns/mir.rs‎

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@@ -0,0 +1,10 @@
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// compile-flags: -Z unpretty=mir
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// build-pass
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fn main() {
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let s = Some(String::new());
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let a;
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match s {
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Some("a") => a = 1234,
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s => a = 4321,
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}
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}

‎src/test/ui/deref-patterns/mir.stdout‎

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@@ -0,0 +1,99 @@
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// WARNING: This output format is intended for human consumers only
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// and is subject to change without notice. Knock yourself out.
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fn main() -> () {
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let mut _0: (); // return place in scope 0 at $DIR/mir.rs:3:11: 3:11
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let _1: std::option::Option<std::string::String>; // in scope 0 at $DIR/mir.rs:4:9: 4:10
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let mut _2: std::string::String; // in scope 0 at $DIR/mir.rs:4:18: 4:31
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let mut _4: &std::string::String; // in scope 0 at $DIR/mir.rs:7:14: 7:17
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let mut _5: &str; // in scope 0 at $DIR/mir.rs:7:14: 7:17
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let mut _6: bool; // in scope 0 at $DIR/mir.rs:7:14: 7:17
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let mut _7: isize; // in scope 0 at $DIR/mir.rs:7:9: 7:18
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let mut _9: bool; // in scope 0 at $DIR/mir.rs:10:1: 10:2
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scope 1 {
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debug s => _1; // in scope 1 at $DIR/mir.rs:4:9: 4:10
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let _3: i32; // in scope 1 at $DIR/mir.rs:5:9: 5:10
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scope 2 {
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debug a => _3; // in scope 2 at $DIR/mir.rs:5:9: 5:10
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let _8: std::option::Option<std::string::String>; // in scope 2 at $DIR/mir.rs:8:9: 8:10
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scope 3 {
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debug s => _8; // in scope 3 at $DIR/mir.rs:8:9: 8:10
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}
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}
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}
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bb0: {
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_9 = const false; // scope 0 at $DIR/mir.rs:4:9: 4:10
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_2 = String::new() -> bb1; // scope 0 at $DIR/mir.rs:4:18: 4:31
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// mir::Constant
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// + span: $DIR/mir.rs:4:18: 4:29
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// + literal: Const { ty: fn() -> String {String::new}, val: Value(Scalar(<ZST>)) }
30+
}
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32+
bb1: {
33+
_9 = const true; // scope 0 at $DIR/mir.rs:4:13: 4:32
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Deinit(_1); // scope 0 at $DIR/mir.rs:4:13: 4:32
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((_1 as Some).0: std::string::String) = move _2; // scope 0 at $DIR/mir.rs:4:13: 4:32
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discriminant(_1) = 1; // scope 0 at $DIR/mir.rs:4:13: 4:32
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_7 = discriminant(_1); // scope 2 at $DIR/mir.rs:6:11: 6:12
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switchInt(move _7) -> [1_isize: bb3, otherwise: bb2]; // scope 2 at $DIR/mir.rs:6:5: 6:12
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}
40+
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bb2: {
42+
_9 = const false; // scope 2 at $DIR/mir.rs:8:9: 8:10
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_8 = move _1; // scope 2 at $DIR/mir.rs:8:9: 8:10
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_3 = const 4321_i32; // scope 3 at $DIR/mir.rs:8:14: 8:22
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drop(_8) -> [return: bb7, unwind: bb12]; // scope 2 at $DIR/mir.rs:8:21: 8:22
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}
47+
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bb3: {
49+
_4 = &((_1 as Some).0: std::string::String); // scope 2 at $DIR/mir.rs:7:14: 7:17
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_5 = <String as Deref>::deref(move _4) -> bb4; // scope 2 at $DIR/mir.rs:7:14: 7:17
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// mir::Constant
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// + span: $DIR/mir.rs:7:14: 7:17
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// + literal: Const { ty: for<'r> fn(&'r String) -> &'r <String as Deref>::Target {<String as Deref>::deref}, val: Value(Scalar(<ZST>)) }
54+
}
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56+
bb4: {
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_6 = <str as PartialEq>::eq(_5, const "a") -> [return: bb5, unwind: bb12]; // scope 2 at $DIR/mir.rs:7:14: 7:17
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// mir::Constant
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// + span: $DIR/mir.rs:7:14: 7:17
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// + literal: Const { ty: for<'r, 's> fn(&'r str, &'s str) -> bool {<str as PartialEq>::eq}, val: Value(Scalar(<ZST>)) }
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// mir::Constant
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// + span: $DIR/mir.rs:7:14: 7:17
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// + literal: Const { ty: &str, val: Value(Slice(..)) }
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}
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bb5: {
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switchInt(move _6) -> [false: bb2, otherwise: bb6]; // scope 2 at $DIR/mir.rs:7:14: 7:17
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}
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bb6: {
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_3 = const 1234_i32; // scope 2 at $DIR/mir.rs:7:22: 7:30
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goto -> bb7; // scope 2 at $DIR/mir.rs:7:22: 7:30
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}
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bb7: {
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switchInt(_9) -> [false: bb8, otherwise: bb10]; // scope 0 at $DIR/mir.rs:10:1: 10:2
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}
78+
79+
bb8: {
80+
_9 = const false; // scope 0 at $DIR/mir.rs:10:1: 10:2
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return; // scope 0 at $DIR/mir.rs:10:2: 10:2
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}
83+
84+
bb9 (cleanup): {
85+
resume; // scope 0 at $DIR/mir.rs:3:1: 10:2
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}
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bb10: {
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drop(_1) -> bb8; // scope 0 at $DIR/mir.rs:10:1: 10:2
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}
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bb11 (cleanup): {
93+
drop(_1) -> bb9; // scope 0 at $DIR/mir.rs:10:1: 10:2
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}
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bb12 (cleanup): {
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switchInt(_9) -> [false: bb9, otherwise: bb11]; // scope 0 at $DIR/mir.rs:10:1: 10:2
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}
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}

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