add const_leak and reject interning non-leaked const_allocate ptrs
#143595
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I'm really excited about this experiment and the movement on const alloc, so thanks for working on it <3 |
oli-obk
reviewed
Jul 7, 2025
| ), | ||
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| // If an allocation is created in an another const, |
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For now we could just error on this. I don't think this should really happen. Either you leaked, then you don't have an owned value anymore, or you didn't, then it got an error
oli-obk
reviewed
Jul 7, 2025
| @@ -7,5 +7,6 @@ use std::intrinsics; | |||
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| const BAR: *mut i32 = unsafe { intrinsics::const_allocate(4, 4) as *mut i32 }; | |||
| //~^ error: mutable pointer in final value of constant | |||
| //~| error: encountered `const_allocate` pointer in final value that was not leaked | |||
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We also need a test that only errors with this error message and looks otherwise benign
oli-obk
reviewed
Jul 7, 2025
| size, | ||
| align, | ||
| interpret::MemoryKind::Machine(MemoryKind::Heap), | ||
| interpret::MemoryKind::Machine(MemoryKind::HeapLeaked), |
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Do we need a separate memory kind? I think the interner will be happy with anything that didn't get deallocated
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Similar to how it interns stack allocations from the trailing expression
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The job Click to see the possible cause of the failure (guessed by this bot) |
oli-obk
reviewed
Jul 7, 2025
| return Err(()); | ||
| }; | ||
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| if matches!(kind, MemoryKind::Machine(x) if x.is_const_heap()) { |
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Please turn this into an exhaustive match on the base memory kind enum.
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Why is this not reusing the may_leak method?
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This isn't about leaking though, it's about interning. I don't think it is the same condition as what Miri's leak check needs?
RalfJung
reviewed
Jul 7, 2025
| kind: MemoryKind<M::MemoryKind>, | ||
| new_kind: MemoryKind<M::MemoryKind>, | ||
| ) -> InterpResult<'tcx, Pointer<M::Provenance>> { | ||
| self.reallocate_ptr_inner( |
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Why does this reallocate? I don't think that is the right semantics. It will be very hard to use this to intern a graph of allocations since you need to mutate the all pointers into the allocation. And it will be impossible to do this in a cyclic graph.
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In terms of naming, I think we said that The original plan I proposed also makes the allocation immutable when it gets marked as global -- basically, this operation should indicate that you are done preparing this allocation and it is ready to be interned. (We actually intern it later as that's easier, but for the API this does not matter.) |
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Implements as discussed on Zulip: #t-compiler/const-eval > const heap
r? @rust-lang/wg-const-eval
Fixes #129233