interpret: add sanity check in dyn upcast to double-check what codegen does #127856
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Some changes occurred to the CTFE / Miri engine cc @rust-lang/miri The Miri subtree was changed cc @rust-lang/miri |
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@bors r+ rollup |
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…oli-obk interpret: add sanity check in dyn upcast to double-check what codegen does For dyn receiver calls, we already have two codepaths: look up the function to call by indexing into the vtable, or alternatively resolve the DefId given the dynamic type of the receiver. With debug assertions enabled, the interpreter does both and compares the results. (Without debug assertions we always use the vtable as it is simpler.) This PR does the same for dyn trait upcasts. However, for casts *not* using the vtable is the easier thing to do, so now the vtable path is the debug-assertion-only path. In particular, there are cases where the vtable does not contain a pointer for upcasts but instead reuses the old pointer: when the supertrait vtable is a prefix of the larger vtable. We don't want to expose this optimization and detect UB if people do a transmute assuming this optimization, so we cannot in general use the vtable indexing path. r? `@oli-obk`
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…iaskrgr Rollup of 7 pull requests Successful merges: - rust-lang#112328 (Feat. adding ext that returns change_time) - rust-lang#126199 (Add `isqrt` to `NonZero<uN>`) - rust-lang#127856 (interpret: add sanity check in dyn upcast to double-check what codegen does) - rust-lang#127934 (Improve error when a compiler/library build fails in `checktools.sh`) - rust-lang#127960 (Cleanup dll/exe filename calculations in `run_make_support`) - rust-lang#127963 (Fix display of logo "border") - rust-lang#127967 (Disable run-make/split-debuginfo test for RISC-V 64) r? `@ghost` `@rustbot` modify labels: rollup
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Rollup merge of rust-lang#127856 - RalfJung:interpret-cast-sanity, r=oli-obk interpret: add sanity check in dyn upcast to double-check what codegen does For dyn receiver calls, we already have two codepaths: look up the function to call by indexing into the vtable, or alternatively resolve the DefId given the dynamic type of the receiver. With debug assertions enabled, the interpreter does both and compares the results. (Without debug assertions we always use the vtable as it is simpler.) This PR does the same for dyn trait upcasts. However, for casts *not* using the vtable is the easier thing to do, so now the vtable path is the debug-assertion-only path. In particular, there are cases where the vtable does not contain a pointer for upcasts but instead reuses the old pointer: when the supertrait vtable is a prefix of the larger vtable. We don't want to expose this optimization and detect UB if people do a transmute assuming this optimization, so we cannot in general use the vtable indexing path. r? ``@oli-obk``
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For dyn receiver calls, we already have two codepaths: look up the function to call by indexing into the vtable, or alternatively resolve the DefId given the dynamic type of the receiver. With debug assertions enabled, the interpreter does both and compares the results. (Without debug assertions we always use the vtable as it is simpler.)
This PR does the same for dyn trait upcasts. However, for casts not using the vtable is the easier thing to do, so now the vtable path is the debug-assertion-only path. In particular, there are cases where the vtable does not contain a pointer for upcasts but instead reuses the old pointer: when the supertrait vtable is a prefix of the larger vtable. We don't want to expose this optimization and detect UB if people do a transmute assuming this optimization, so we cannot in general use the vtable indexing path.
r? @oli-obk