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fix(transmute): accept MaybeUninit reinterpretation #1017

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fix(transmute): accept MaybeUninit reinterpretation #1017

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17 changes: 4 additions & 13 deletions kmir/src/kmir/kdist/mir-semantics/rt/data.md
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Original file line number Diff line number Diff line change
Expand Up @@ -1838,24 +1838,15 @@ the safety of this cast. The logic of the semantics and saftey of this cast for
```k
syntax MIRError ::= "#UBInvalidTransmuteMaybeUninit"
rule <k>
#cast( _VAL:Value , castKindTransmute , TY_FROM , TY_TO )
#cast( VAL:Value , castKindTransmute , _TY_FROM , TY_TO )
=>
#UBInvalidTransmuteMaybeUninit
Union(fieldIdx(1), Aggregate(variantIdx(0), ListItem(VAL) .List))
...
</k>
requires #isUnionType(lookupTy(TY_TO))
andBool #typeNameIs(lookupTy(TY_TO), "std::mem::MaybeUninit<")
andBool TY_FROM =/=K getFieldTy(#lookupMaybeTy(getFieldTy(lookupTy(TY_TO), 1)), 0)

rule <k>
#cast( VAL:Value , castKindTransmute , TY_FROM , TY_TO )
=>
Union( fieldIdx ( 1 ) , Aggregate ( variantIdx ( 0 ) , ListItem(VAL) .List ))
...
</k>
requires #isUnionType(lookupTy(TY_TO))
andBool #typeNameIs(lookupTy(TY_TO), "std::mem::MaybeUninit<")
andBool TY_FROM ==K getFieldTy(#lookupMaybeTy(getFieldTy(lookupTy(TY_TO), 1)), 0)
// `MaybeUninit<T>` accepts arbitrary bit patterns, so any value can be
// reinterpreted into the union's initialized field.

// Converting static or dynamic sized array of `T` to array of `std::mem::MaybeUninit<T>`.
// FIXME: Might need to check sizes as this cast could come from transmute_unchecked
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17 changes: 0 additions & 17 deletions kmir/src/tests/integration/data/prove-rs/show/transmute-maybe-uninit-fail.main.expected
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17 changes: 17 additions & 0 deletions kmir/src/tests/integration/data/prove-rs/show/transmute-maybe-uninit-i128.main.expected
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@@ -0,0 +1,17 @@

┌─ 1 (root, init)
│ #execTerminator ( terminator ( ... kind: terminatorKindCall ( ... func: operandC
│ span: 0
│
│ (77 steps)
├─ 3 (terminal)
│ #EndProgram ~> .K
│ function: main
│
┊ constraint: true
┊ subst: ...
└─ 2 (leaf, target, terminal)
#EndProgram ~> .K



1 change: 0 additions & 1 deletion ...a/prove-rs/transmute-maybe-uninit-fail.rs → ...a/prove-rs/transmute-maybe-uninit-i128.rs
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Expand Up @@ -4,7 +4,6 @@ use std::mem::MaybeUninit;
fn main() {
unsafe {
let maybe_unsigned = std::intrinsics::transmute::<i128, MaybeUninit::<u128>>(9999);
// Note different types ^^^^ ^^^^
assert!(maybe_unsigned.assume_init() == 9999);
}
}
2 changes: 1 addition & 1 deletion kmir/src/tests/integration/test_integration.py
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Expand Up @@ -60,7 +60,7 @@
'assert-inhabited-fail',
'iterator-simple',
'unions-fail',
'transmute-maybe-uninit-fail',
'transmute-maybe-uninit-i128',
'ptr-through-wrapper-fail',
'test_offset_from-fail',
'ref-ptr-cast-elem-fail',
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