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read_via_copy: don't prematurely optimize away the read

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This commit is contained in:
Ralf Jung 2023-09-04 15:32:07 +02:00
parent a989e25f1b
commit 7093903ba7
5 changed files with 39 additions and 16 deletions
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23
compiler/rustc_mir_transform/src/lower_intrinsics.rs
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@ -176,23 +176,22 @@ impl<'tcx> MirPass<'tcx> for LowerIntrinsics {
} else {
span_bug!(terminator.source_info.span, "Only passing a local is supported");
};
// Add new statement at the end of the block that does the read, and patch
// up the terminator.
block.statements.push(Statement {
source_info: terminator.source_info,
kind: StatementKind::Assign(Box::new((
*destination,
Rvalue::Use(Operand::Copy(derefed_place)),
))),
});
terminator.kind = match *target {
None => {
// No target means this read something uninhabited,
// so it must be unreachable, and we don't need to
// preserve the assignment either.
// so it must be unreachable.
TerminatorKind::Unreachable
}
Some(target) => {
block.statements.push(Statement {
source_info: terminator.source_info,
kind: StatementKind::Assign(Box::new((
*destination,
Rvalue::Use(Operand::Copy(derefed_place)),
))),
});
TerminatorKind::Goto { target }
}
Some(target) => TerminatorKind::Goto { target },
}
}
sym::write_via_move => {

1
tests/mir-opt/lower_intrinsics.read_via_copy_uninhabited.LowerIntrinsics.panic-abort.diff
View File

@ -12,6 +12,7 @@
StorageLive(_2);
_2 = &raw const (*_1);
- _0 = read_via_copy::<Never>(move _2) -> unwind unreachable;
+ _0 = (*_2);
+ unreachable;
}
}

1
tests/mir-opt/lower_intrinsics.read_via_copy_uninhabited.LowerIntrinsics.panic-unwind.diff
View File

@ -12,6 +12,7 @@
StorageLive(_2);
_2 = &raw const (*_1);
- _0 = read_via_copy::<Never>(move _2) -> unwind unreachable;
+ _0 = (*_2);
+ unreachable;
}
}

16
tests/ui/consts/const-eval/ub-uninhabit.rs
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@ -1,7 +1,10 @@
// Strip out raw byte dumps to make comparison platform-independent:
// normalize-stderr-test "(the raw bytes of the constant) \(size: [0-9]*, align: [0-9]*\)" -> "$1 (size: $$SIZE, align: $$ALIGN)"
// normalize-stderr-test "([0-9a-f][0-9a-f] |╾─*a(lloc)?[0-9]+(\+[a-z0-9]+)?─*╼ )+ *│.*" -> "HEX_DUMP"
#![feature(core_intrinsics)]
#![feature(never_type)]
use std::intrinsics;
use std::mem;
#[derive(Copy, Clone)]
@ -15,11 +18,24 @@ union MaybeUninit<T: Copy> {
const BAD_BAD_BAD: Bar = unsafe { MaybeUninit { uninit: () }.init };
//~^ ERROR evaluation of constant value failed
//~| constructing invalid value
const BAD_BAD_REF: &Bar = unsafe { mem::transmute(1usize) };
//~^ ERROR it is undefined behavior to use this value
//~| constructing invalid value
const BAD_BAD_ARRAY: [Bar; 1] = unsafe { MaybeUninit { uninit: () }.init };
//~^ ERROR evaluation of constant value failed
//~| constructing invalid value
const READ_NEVER: () = unsafe {
let mem = [0u32; 8];
let ptr = mem.as_ptr().cast::<!>();
let _val = intrinsics::read_via_copy(ptr);
//~^ ERROR evaluation of constant value failed
//~| constructing invalid value
};
fn main() {}

14
tests/ui/consts/const-eval/ub-uninhabit.stderr
View File

@ -1,11 +1,11 @@
error[E0080]: evaluation of constant value failed
--> $DIR/ub-uninhabit.rs:16:35
--> $DIR/ub-uninhabit.rs:19:35
|
LL | const BAD_BAD_BAD: Bar = unsafe { MaybeUninit { uninit: () }.init };
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value: encountered a value of uninhabited type `Bar`
error[E0080]: it is undefined behavior to use this value
--> $DIR/ub-uninhabit.rs:19:1
--> $DIR/ub-uninhabit.rs:23:1
|
LL | const BAD_BAD_REF: &Bar = unsafe { mem::transmute(1usize) };
| ^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value: encountered a reference pointing to uninhabited type Bar
@ -16,11 +16,17 @@ LL | const BAD_BAD_REF: &Bar = unsafe { mem::transmute(1usize) };
}
error[E0080]: evaluation of constant value failed
--> $DIR/ub-uninhabit.rs:22:42
--> $DIR/ub-uninhabit.rs:27:42
|
LL | const BAD_BAD_ARRAY: [Bar; 1] = unsafe { MaybeUninit { uninit: () }.init };
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value at [0]: encountered a value of uninhabited type `Bar`
error: aborting due to 3 previous errors
error[E0080]: evaluation of constant value failed
--> $DIR/ub-uninhabit.rs:35:16
|
LL | let _val = intrinsics::read_via_copy(ptr);
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value: encountered a value of the never type `!`
error: aborting due to 4 previous errors
For more information about this error, try `rustc --explain E0080`.