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add overlap check when copying op #97639

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add overlap check when copying op #97639

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2668b2a
add overlap check when copying an imm
SparrowLii Jun 2, 2022
03509a6
correct overlap check
SparrowLii Jun 2, 2022
42c58cd
correct condition statement
SparrowLii Jun 2, 2022
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2 changes: 1 addition & 1 deletion compiler/rustc_const_eval/src/interpret/memory.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1216,7 +1216,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
dest_offset: Size,
size: Size,
) -> bool {
let overlaps = |a, b| a <= b && b < a + size;
let overlaps = |a, b| a <= b && b - a < size;
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Please add a comment explaining why the subtraction cannot overflow.

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we could rewrite this as a.checked_sub(b).map_or(false, |s| s < size)

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@RalfJung RalfJung Jun 2, 2022 •
edited
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Not sure if that makes it any clearer; why is false the right default?

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Ok, I think we can just comment that since `a <= b`, `b - a` will not overflows

src_id == dest_id
&& (overlaps(src_offset, dest_offset) || overlaps(dest_offset, src_offset))
}
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