Intptrcast model #61668
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Intptrcast model #61668
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r? @estebank (rust_highfive has picked a reviewer for you, use r? to override) |
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| @@ -314,13 +314,23 @@ impl<'a, 'mir, 'tcx, M: Machine<'a, 'mir, 'tcx>> InterpretCx<'a, 'mir, 'tcx, M> | |||
| right.to_scalar_ptr()?.is_ptr() || | |||
| bin_op == mir::BinOp::Offset | |||
| { | |||
| return M::ptr_op(self, bin_op, left, right); | |||
| if left.layout.ty.is_integral() && right.layout.ty.is_integral() { | |||
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why was this change done? It seems good, but unrelated to this PR right now
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It was done per @RalfJung suggestions. Here are his comments on the matter:
basically, if we have integer addresses, we have two cases:
either left.layout.ty.is_integral() && right.layout.ty.is_integral(). then both sides should be ptr-to-int-cast, and we proceed with binary_int_op.
or bin_op == mir::BinOp::Offset, then call M::ptr_op.
if we dont have integer addresses, behavior should be unchanged.
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ah, this is then indeed where your test output changes come from: force_bits is guaranteed to fail, since we already know that either left or right is a Scalar::Ptr (as per the if condition in line 313 and 314)
I don't think we should do this here, but instead miri can do this in ptr_op once it actually supports intptr. If we merged this, there would be no way for miri to do a change that will fix its test suite other than implementing intptr.
It's also useless for const eval, so I think it should not be in the engine.
@RalfJung or am I missing something?
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Well now I can't look any more because the diff is broken. :/
But I somehow didn't like going through Miri and back when we have ptr-int-casts available. The code flow would be somewhat weird: Miri would do force_bits and then call back to here, and endless recursion would be prevented because things would then not be pointers any more.
Notice that I specifically said "if we dont have integer addresses, behavior should be unchanged" in my plan; the idea was that we would have some way to detect that (maybe check the force functions return value for Err?). But maybe you are right and it makes more sense to do all of that in Miri.
I just really don't like seeing any value-based dispatching in the code here. Dispatching should be purely type-based...
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Jun 12, 2019
src/librustc_mir/interpret/memory.rs
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| ) -> EvalResult<'tcx, Pointer<M::PointerTag>> { | ||
| match scalar { | ||
| Scalar::Ptr(ptr) => Ok(ptr), | ||
| _ => M::int_to_ptr(scalar.to_u64()?, &self.extra) |
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Otherwise you'll get a "read undef bytes" error when interpreting 32 bit code
Suggested change
| _ => M::int_to_ptr(scalar.to_u64()?, &self.extra) | |
| _ => M::int_to_ptr(scalar.to_usize(self)?, &self.extra) |
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We talked about this on zulip and I thought I've done it, I'll fix it
| @@ -314,13 +314,23 @@ impl<'a, 'mir, 'tcx, M: Machine<'a, 'mir, 'tcx>> InterpretCx<'a, 'mir, 'tcx, M> | |||
| right.to_scalar_ptr()?.is_ptr() || | |||
| bin_op == mir::BinOp::Offset | |||
| { | |||
| return M::ptr_op(self, bin_op, left, right); | |||
| if left.layout.ty.is_integral() && right.layout.ty.is_integral() { | |||
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ah, this is then indeed where your test output changes come from: force_bits is guaranteed to fail, since we already know that either left or right is a Scalar::Ptr (as per the if condition in line 313 and 314)
I don't think we should do this here, but instead miri can do this in ptr_op once it actually supports intptr. If we merged this, there would be no way for miri to do a change that will fix its test suite other than implementing intptr.
It's also useless for const eval, so I think it should not be in the engine.
@RalfJung or am I missing something?
This uses a well-known branchless implementation of `signum`. Its `const`-ness is unstable and requires `#![feature(const_int_sign)]`.
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I messed up solving the conflicts, I'll redo the changes on a fresh branch and do another PR |
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…=oli-obk prepare for Intptrcast model rust-lang#61668 done right (I hope so). r? @RalfJung @oli-obk
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…=oli-obk prepare for Intptrcast model rust-lang#61668 done right (I hope so). r? @RalfJung @oli-obk
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…=oli-obk prepare for Intptrcast model rust-lang#61668 done right (I hope so). r? @RalfJung @oli-obk
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rust-lang/miri#224