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rustc_mir: insert a dummy access to places being matched on, when building MIR. #48092

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Feb 11, 2018
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rustc_mir: insert a dummy access to places being matched on, when building MIR. #48092

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4aa66db
rustc: don't ICE when using Rvalue::Discriminant on a non-ADT.
eddyb Feb 8, 2018
8af134e
rustc_mir: insert a dummy access to places being matched on, when bui…
eddyb Feb 9, 2018
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5 changes: 2 additions & 3 deletions src/librustc/mir/tcx.rs
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Expand Up @@ -182,9 +182,8 @@ impl<'tcx> Rvalue<'tcx> {
if let ty::TyAdt(adt_def, _) = ty.sty {
adt_def.repr.discr_type().to_ty(tcx)
} else {
// Undefined behaviour, bug for now; may want to return something for
// the `discriminant` intrinsic later.
bug!("Rvalue::Discriminant on Place of type {:?}", ty);
// This can only be `0`, for now, so `u8` will suffice.
tcx.types.u8
}
}
Rvalue::NullaryOp(NullOp::Box, t) => tcx.mk_box(t),
Expand Down
16 changes: 16 additions & 0 deletions src/librustc_mir/build/matches/mod.rs
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Expand Up @@ -38,6 +38,22 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
-> BlockAnd<()> {
let discriminant_place = unpack!(block = self.as_place(block, discriminant));

// Matching on a `discriminant_place` with an uninhabited type doesn't
// generate any memory reads by itself, and so if the place "expression"
// contains unsafe operations like raw pointer dereferences or union
// field projections, we wouldn't know to require an `unsafe` block
// around a `match` equivalent to `std::intrinsics::unreachable()`.
// See issue #47412 for this hole being discovered in the wild.
//
// HACK(eddyb) Work around the above issue by adding a dummy inspection
// of `discriminant_place`, specifically by applying `Rvalue::Discriminant`
// (which will work regardless of type) and storing the result in a temp.
let dummy_source_info = self.source_info(span);
let dummy_access = Rvalue::Discriminant(discriminant_place.clone());
let dummy_ty = dummy_access.ty(&self.local_decls, self.hir.tcx());
let dummy_temp = self.temp(dummy_ty, dummy_source_info.span);
self.cfg.push_assign(block, dummy_source_info, &dummy_temp, dummy_access);

let mut arm_blocks = ArmBlocks {
blocks: arms.iter()
.map(|_| self.cfg.start_new_block())
Expand Down
28 changes: 14 additions & 14 deletions src/test/compile-fail/borrowck/borrowck-describe-lvalue.rs
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Expand Up @@ -72,7 +72,7 @@ fn main() {
{
let mut e = Baz::X(2);
let _e0 = e.x();
match e {
match e { //[mir]~ ERROR cannot use `e` because it was mutably borrowed
Baz::X(value) => value
//[ast]~^ ERROR cannot use `e.0` because it was mutably borrowed
//[mir]~^^ ERROR cannot use `e.0` because it was mutably borrowed
Expand Down Expand Up @@ -110,7 +110,7 @@ fn main() {
{
let mut e = Box::new(Baz::X(3));
let _e0 = e.x();
match *e {
match *e { //[mir]~ ERROR cannot use `*e` because it was mutably borrowed
Baz::X(value) => value
//[ast]~^ ERROR cannot use `e.0` because it was mutably borrowed
//[mir]~^^ ERROR cannot use `e.0` because it was mutably borrowed
Expand All @@ -127,25 +127,25 @@ fn main() {
{
let mut v = &[1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
let _v = &mut v;
match v {
match v { //[mir]~ ERROR cannot use `v` because it was mutably borrowed
&[x, _, .., _, _] => println!("{}", x),
//[ast]~^ ERROR cannot use `v[..]` because it was mutably borrowed
//[mir]~^^ ERROR cannot use `v[..]` because it was mutably borrowed
_ => panic!("other case"),
}
match v {
match v { //[mir]~ ERROR cannot use `v` because it was mutably borrowed
&[_, x, .., _, _] => println!("{}", x),
//[ast]~^ ERROR cannot use `v[..]` because it was mutably borrowed
//[mir]~^^ ERROR cannot use `v[..]` because it was mutably borrowed
_ => panic!("other case"),
}
match v {
match v { //[mir]~ ERROR cannot use `v` because it was mutably borrowed
&[_, _, .., x, _] => println!("{}", x),
//[ast]~^ ERROR cannot use `v[..]` because it was mutably borrowed
//[mir]~^^ ERROR cannot use `v[..]` because it was mutably borrowed
_ => panic!("other case"),
}
match v {
match v { //[mir]~ ERROR cannot use `v` because it was mutably borrowed
&[_, _, .., _, x] => println!("{}", x),
//[ast]~^ ERROR cannot use `v[..]` because it was mutably borrowed
//[mir]~^^ ERROR cannot use `v[..]` because it was mutably borrowed
Expand All @@ -156,25 +156,25 @@ fn main() {
{
let mut v = &[1, 2, 3, 4, 5];
let _v = &mut v;
match v {
match v { //[mir]~ ERROR cannot use `v` because it was mutably borrowed
&[x..] => println!("{:?}", x),
//[ast]~^ ERROR cannot use `v[..]` because it was mutably borrowed
//[mir]~^^ ERROR cannot use `v[..]` because it was mutably borrowed
_ => panic!("other case"),
}
match v {
match v { //[mir]~ ERROR cannot use `v` because it was mutably borrowed
&[_, x..] => println!("{:?}", x),
//[ast]~^ ERROR cannot use `v[..]` because it was mutably borrowed
//[mir]~^^ ERROR cannot use `v[..]` because it was mutably borrowed
_ => panic!("other case"),
}
match v {
match v { //[mir]~ ERROR cannot use `v` because it was mutably borrowed
&[x.., _] => println!("{:?}", x),
//[ast]~^ ERROR cannot use `v[..]` because it was mutably borrowed
//[mir]~^^ ERROR cannot use `v[..]` because it was mutably borrowed
_ => panic!("other case"),
}
match v {
match v { //[mir]~ ERROR cannot use `v` because it was mutably borrowed
&[_, x.., _] => println!("{:?}", x),
//[ast]~^ ERROR cannot use `v[..]` because it was mutably borrowed
//[mir]~^^ ERROR cannot use `v[..]` because it was mutably borrowed
Expand All @@ -187,7 +187,7 @@ fn main() {

let mut e = E::A(3);
let _e = &mut e;
match e {
match e { //[mir]~ ERROR cannot use `e` because it was mutably borrowed
E::A(ref ax) =>
//[ast]~^ ERROR cannot borrow `e.0` as immutable because `e` is also borrowed as mutable
//[mir]~^^ ERROR cannot borrow `e.0` as immutable because it is also borrowed as mutable
Expand All @@ -205,14 +205,14 @@ fn main() {
struct S { x: F, y: (u32, u32), };
let mut s = S { x: F { x: 1, y: 2}, y: (999, 998) };
let _s = &mut s;
match s {
match s { //[mir]~ ERROR cannot use `s` because it was mutably borrowed
S { y: (ref y0, _), .. } =>
//[ast]~^ ERROR cannot borrow `s.y.0` as immutable because `s` is also borrowed as mutable
//[mir]~^^ ERROR cannot borrow `s.y.0` as immutable because it is also borrowed as mutable
println!("y0: {:?}", y0),
_ => panic!("other case"),
}
match s {
match s { //[mir]~ ERROR cannot use `s` because it was mutably borrowed
S { x: F { y: ref x0, .. }, .. } =>
//[ast]~^ ERROR cannot borrow `s.x.y` as immutable because `s` is also borrowed as mutable
//[mir]~^^ ERROR cannot borrow `s.x.y` as immutable because it is also borrowed as mutable
Expand Down Expand Up @@ -263,7 +263,7 @@ fn main() {
struct F {x: u32, y: u32};
let mut v = &[F{x: 1, y: 2}, F{x: 3, y: 4}];
let _v = &mut v;
match v {
match v { //[mir]~ ERROR cannot use `v` because it was mutably borrowed
&[_, F {x: ref xf, ..}] => println!("{}", xf),
//[mir]~^ ERROR cannot borrow `v[..].x` as immutable because it is also borrowed as mutable
// No errors in AST
Expand Down
4 changes: 2 additions & 2 deletions src/test/compile-fail/borrowck/borrowck-match-already-borrowed.rs
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Expand Up @@ -19,7 +19,7 @@ enum Foo {
fn match_enum() {
let mut foo = Foo::B;
let p = &mut foo;
let _ = match foo {
let _ = match foo { //[mir]~ ERROR [E0503]
Foo::B => 1, //[mir]~ ERROR [E0503]
_ => 2,
Foo::A(x) => x //[ast]~ ERROR [E0503]
Expand All @@ -31,7 +31,7 @@ fn match_enum() {
fn main() {
let mut x = 1;
let _x = &mut x;
let _ = match x {
let _ = match x { //[mir]~ ERROR [E0503]
x => x + 1, //[ast]~ ERROR [E0503]
//[mir]~^ ERROR [E0503]
y => y + 2, //[ast]~ ERROR [E0503]
Expand Down
31 changes: 31 additions & 0 deletions src/test/compile-fail/issue-47412.rs
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@@ -0,0 +1,31 @@
// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

#[derive(Copy, Clone)]
enum Void {}

// Tests that we detect unsafe places (specifically, union fields and
// raw pointer dereferences), even when they're matched on while having
// an uninhabited type (equivalent to `std::intrinsics::unreachable()`).

fn union_field() {
union Union { unit: (), void: Void }
let u = Union { unit: () };
match u.void {}
//~^ ERROR access to union field requires unsafe function or block
}

fn raw_ptr_deref() {
let ptr = std::ptr::null::<Void>();
match *ptr {}
//~^ ERROR dereference of raw pointer requires unsafe function or block
}

fn main() {}
107 changes: 55 additions & 52 deletions src/test/mir-opt/match_false_edges.rs
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Expand Up @@ -53,17 +53,18 @@ fn main() {
// bb0: {
// ...
// _2 = std::option::Option<i32>::Some(const 42i32,);
// _5 = discriminant(_2);
// switchInt(move _5) -> [0isize: bb6, 1isize: bb4, otherwise: bb8];
// _3 = discriminant(_2);
// _6 = discriminant(_2);
// switchInt(move _6) -> [0isize: bb6, 1isize: bb4, otherwise: bb8];
// }
// bb1: {
// resume;
// }
// bb2: { // arm1
// StorageLive(_7);
// _7 = _3;
// _1 = (const 1i32, move _7);
// StorageDead(_7);
// StorageLive(_8);
// _8 = _4;
// _1 = (const 1i32, move _8);
// StorageDead(_8);
// goto -> bb13;
// }
// bb3: { // binding3(empty) and arm3
Expand All @@ -86,24 +87,24 @@ fn main() {
// unreachable;
// }
// bb9: { // binding1 and guard
// StorageLive(_3);
// _3 = ((_2 as Some).0: i32);
// StorageLive(_6);
// _6 = const guard() -> [return: bb10, unwind: bb1];
// StorageLive(_4);
// _4 = ((_2 as Some).0: i32);
// StorageLive(_7);
// _7 = const guard() -> [return: bb10, unwind: bb1];
// }
// bb10: { // end of guard
// switchInt(move _6) -> [0u8: bb11, otherwise: bb2];
// switchInt(move _7) -> [0u8: bb11, otherwise: bb2];
// }
// bb11: { // to pre_binding2
// falseEdges -> [real: bb5, imaginary: bb5];
// }
// bb12: { // bindingNoLandingPads.before.mir2 and arm2
// StorageLive(_4);
// _4 = ((_2 as Some).0: i32);
// StorageLive(_8);
// _8 = _4;
// _1 = (const 2i32, move _8);
// StorageDead(_8);
// StorageLive(_5);
// _5 = ((_2 as Some).0: i32);
// StorageLive(_9);
// _9 = _5;
// _1 = (const 2i32, move _9);
// StorageDead(_9);
// goto -> bb13;
// }
// bb13: {
Expand All @@ -116,17 +117,18 @@ fn main() {
// bb0: {
// ...
// _2 = std::option::Option<i32>::Some(const 42i32,);
// _5 = discriminant(_2);
// switchInt(move _5) -> [0isize: bb5, 1isize: bb4, otherwise: bb8];
// _3 = discriminant(_2);
// _6 = discriminant(_2);
// switchInt(move _6) -> [0isize: bb5, 1isize: bb4, otherwise: bb8];
// }
// bb1: {
// resume;
// }
// bb2: { // arm1
// StorageLive(_7);
// _7 = _3;
// _1 = (const 1i32, move _7);
// StorageDead(_7);
// StorageLive(_8);
// _8 = _4;
// _1 = (const 1i32, move _8);
// StorageDead(_8);
// goto -> bb13;
// }
// bb3: { // binding3(empty) and arm3
Expand All @@ -149,24 +151,24 @@ fn main() {
// unreachable;
// }
// bb9: { // binding1 and guard
// StorageLive(_3);
// _3 = ((_2 as Some).0: i32);
// StorageLive(_6);
// _6 = const guard() -> [return: bb10, unwind: bb1];
// StorageLive(_4);
// _4 = ((_2 as Some).0: i32);
// StorageLive(_7);
// _7 = const guard() -> [return: bb10, unwind: bb1];
// }
// bb10: { // end of guard
// switchInt(move _6) -> [0u8: bb11, otherwise: bb2];
// switchInt(move _7) -> [0u8: bb11, otherwise: bb2];
// }
// bb11: { // to pre_binding2
// falseEdges -> [real: bb6, imaginary: bb5];
// }
// bb12: { // binding2 and arm2
// StorageLive(_4);
// _4 = ((_2 as Some).0: i32);
// StorageLive(_8);
// _8 = _4;
// _1 = (const 2i32, move _8);
// StorageDead(_8);
// StorageLive(_5);
// _5 = ((_2 as Some).0: i32);
// StorageLive(_9);
// _9 = _5;
// _1 = (const 2i32, move _9);
// StorageDead(_9);
// goto -> bb13;
// }
// bb13: {
Expand All @@ -179,8 +181,9 @@ fn main() {
// bb0: {
// ...
// _2 = std::option::Option<i32>::Some(const 1i32,);
// _7 = discriminant(_2);
// switchInt(move _7) -> [1isize: bb4, otherwise: bb5];
// _3 = discriminant(_2);
// _8 = discriminant(_2);
// switchInt(move _8) -> [1isize: bb4, otherwise: bb5];
// }
// bb1: {
// resume;
Expand Down Expand Up @@ -210,41 +213,41 @@ fn main() {
// unreachable;
// }
// bb9: { // binding1: Some(w) if guard()
// StorageLive(_3);
// _3 = ((_2 as Some).0: i32);
// StorageLive(_8);
// _8 = const guard() -> [return: bb10, unwind: bb1];
// StorageLive(_4);
// _4 = ((_2 as Some).0: i32);
// StorageLive(_9);
// _9 = const guard() -> [return: bb10, unwind: bb1];
// }
// bb10: { //end of guard
// switchInt(move _8) -> [0u8: bb11, otherwise: bb2];
// switchInt(move _9) -> [0u8: bb11, otherwise: bb2];
// }
// bb11: { // to pre_binding2
// falseEdges -> [real: bb5, imaginary: bb5];
// }
// bb12: { // binding2 & arm2
// StorageLive(_4);
// _4 = _2;
// StorageLive(_5);
// _5 = _2;
// _1 = const 2i32;
// goto -> bb17;
// }
// bb13: { // binding3: Some(y) if guard2(y)
// StorageLive(_5);
// _5 = ((_2 as Some).0: i32);
// StorageLive(_10);
// StorageLive(_6);
// _6 = ((_2 as Some).0: i32);
// StorageLive(_11);
// _11 = _5;
// _10 = const guard2(move _11) -> [return: bb14, unwind: bb1];
// StorageLive(_12);
// _12 = _6;
// _11 = const guard2(move _12) -> [return: bb14, unwind: bb1];
// }
// bb14: { // end of guard2
// StorageDead(_11);
// switchInt(move _10) -> [0u8: bb15, otherwise: bb3];
// StorageDead(_12);
// switchInt(move _11) -> [0u8: bb15, otherwise: bb3];
// }
// bb15: { // to pre_binding4
// falseEdges -> [real: bb7, imaginary: bb7];
// }
// bb16: { // binding4 & arm4
// StorageLive(_6);
// _6 = _2;
// StorageLive(_7);
// _7 = _2;
// _1 = const 4i32;
// goto -> bb17;
// }
Expand Down
1 change: 1 addition & 0 deletions src/test/ui/borrowck/issue-41962.rs
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Expand Up @@ -18,6 +18,7 @@ pub fn main(){
//~^ ERROR use of partially moved value: `maybe` (Ast) [E0382]
//~| ERROR use of moved value: `(maybe as std::prelude::v1::Some).0` (Ast) [E0382]
//~| ERROR use of moved value: `maybe` (Mir) [E0382]
//~| ERROR use of moved value: `maybe` (Mir) [E0382]
//~| ERROR use of moved value: `maybe.0` (Mir) [E0382]
}
}
Expand Down
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