Auto merge of #115531 - RalfJung:read_via_copy, r=scottmcm

read_via_copy: don't prematurely optimize away the read

Always do the read to ensure consistent UB error messages in const-eval/Miri.

r? `@scottmcm`
This commit is contained in:
bors 2023-09-05 03:45:17 +00:00
commit 626a6ab93f
5 changed files with 39 additions and 16 deletions

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@ -176,23 +176,22 @@ impl<'tcx> MirPass<'tcx> for LowerIntrinsics {
} else { } else {
span_bug!(terminator.source_info.span, "Only passing a local is supported"); 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 { terminator.kind = match *target {
None => { None => {
// No target means this read something uninhabited, // No target means this read something uninhabited,
// so it must be unreachable, and we don't need to // so it must be unreachable.
// preserve the assignment either.
TerminatorKind::Unreachable TerminatorKind::Unreachable
} }
Some(target) => { Some(target) => TerminatorKind::Goto { 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 }
}
} }
} }
sym::write_via_move => { sym::write_via_move => {

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

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

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@ -1,7 +1,10 @@
// Strip out raw byte dumps to make comparison platform-independent: // 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 "(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" // 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; use std::mem;
#[derive(Copy, Clone)] #[derive(Copy, Clone)]
@ -15,11 +18,24 @@ union MaybeUninit<T: Copy> {
const BAD_BAD_BAD: Bar = unsafe { MaybeUninit { uninit: () }.init }; const BAD_BAD_BAD: Bar = unsafe { MaybeUninit { uninit: () }.init };
//~^ ERROR evaluation of constant value failed //~^ ERROR evaluation of constant value failed
//~| constructing invalid value
const BAD_BAD_REF: &Bar = unsafe { mem::transmute(1usize) }; const BAD_BAD_REF: &Bar = unsafe { mem::transmute(1usize) };
//~^ ERROR it is undefined behavior to use this value //~^ ERROR it is undefined behavior to use this value
//~| constructing invalid value
const BAD_BAD_ARRAY: [Bar; 1] = unsafe { MaybeUninit { uninit: () }.init }; const BAD_BAD_ARRAY: [Bar; 1] = unsafe { MaybeUninit { uninit: () }.init };
//~^ ERROR evaluation of constant value failed //~^ 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() {} fn main() {}

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@ -1,11 +1,11 @@
error[E0080]: evaluation of constant value failed 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 }; LL | const BAD_BAD_BAD: Bar = unsafe { MaybeUninit { uninit: () }.init };
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value: encountered a value of uninhabited type `Bar` | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value: encountered a value of uninhabited type `Bar`
error[E0080]: it is undefined behavior to use this value 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) }; LL | const BAD_BAD_REF: &Bar = unsafe { mem::transmute(1usize) };
| ^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value: encountered a reference pointing to uninhabited type Bar | ^^^^^^^^^^^^^^^^^^^^^^^ 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 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 }; LL | const BAD_BAD_ARRAY: [Bar; 1] = unsafe { MaybeUninit { uninit: () }.init };
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value at [0]: encountered a value of uninhabited type `Bar` | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 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`. For more information about this error, try `rustc --explain E0080`.