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Disable field reordering for repr(int). - #56887
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rust-highfive
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Dec 16, 2018
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(rust_highfive has picked a reviewer for you, use r? to override) |
emilio
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Dec 16, 2018
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r? @eddyb |
emilio
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Dec 16, 2018
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The order of commits is the opposite github shows because github doesn't show the topological order... :( Anyway. cc @BorisChiou, I think this is the problem you hit with cbindgen that time. |
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RFC rust-lang#2195 specifies that a repr(int) enum such as: #[repr(u8)] enum MyEnum { B { x: u8, y: i16, z: u8 }, } has a layout that is equivalent to: #[repr(C)] enum MyEnumVariantB { tag: u8, x: u8, y: i16, z: u8 }, However this isn't actually implemented, with the actual layout being roughly equivalent to: union MyEnumPayload { B { x: u8, y: i16, z: u8 }, } #[repr(packed)] struct MyEnum { tag: u8, payload: MyEnumPayload, } Thus the variant payload is *not* subject to repr(C) ordering rules, and gets re-ordered as `{ x: u8, z: u8, z: i16 }` The existing tests added in pull-req rust-lang#45688 fail to catch this as the repr(C) ordering just happens to match the current Rust ordering in this case; adding a third field reveals the problem.
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| pub fn inhibit_struct_field_reordering_opt(&self) -> bool { | ||
| !(self.flags & ReprFlags::IS_UNOPTIMISABLE).is_empty() || (self.pack == 1) | ||
| self.flags.intersects(ReprFlags::IS_UNOPTIMISABLE) || self.pack == 1 || | ||
| self.int.is_some() |
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cc @rkruppe@nagisa This seems somewhat fragile (I mean the pre-existing code).
The check for pack == 1 means things will still be reordered with #[repr(packed(N))], is that intentional?
Also, it seems to me that inhibit_enum_layout_opt is a subset of this function and maybe we should have just one function that checks all conditions?
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The repr RFC does not specify any behaviour /wrt repr(packed(N)) for enums and I’m not sure I recall us guaranteeing that repr(packed) specifies any representation and the reference seems to agree.
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In fact as per strict reading of the reference, self.pack == 1 inhibiting reordering would be somewhat wrong, as it should cause "packing" for the original ordering, but since the "default" ordering is not specified, it seems to be fine either way...
eddyb
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Dec 19, 2018
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@bors r+ |
bors
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Dec 19, 2018
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📌 Commit d84bdba has been approved by |
emilyalbini added a commit
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Dec 20, 2018
Disable field reordering for repr(int). This fixes the problem that the test in rust-lang#56619 uncovers. Closesrust-lang#56619.
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Dec 21, 2018
Disable field reordering for repr(int). This fixes the problem that the test in rust-lang#56619 uncovers. Closesrust-lang#56619.
emilyalbini added a commit
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Dec 21, 2018
Disable field reordering for repr(int). This fixes the problem that the test in rust-lang#56619 uncovers. Closesrust-lang#56619.
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Dec 21, 2018
Rollup of 20 pull requests Successful merges: - #56802 (Add DoubleEndedIterator::nth_back) - #56842 (Add unstable VecDeque::rotate_{left|right}) - #56869 (Reduce search-index.js size) - #56887 (Disable field reordering for repr(int).) - #56892 (rustc: Update Clang used to build LLVM on Linux) - #56909 (static eval: Do not ICE on layout size overflow) - #56914 (Ignore ui/target-feature-gate on sparc, sparc64, powerpc, powerpc64 and powerpc64le) - #56917 (Simplify MIR generation for logical operations) - #56919 (Remove a wrong multiplier on relocation offset computation) - #56933 (Add --progress to git submodule commands in x.py) - #56941 (deny intra-doc link resolution failures in libstd) - #56964 (Remove `TokenStream::JointTree`.) - #56970 (Mem uninit doc ptr drop) - #56973 (make basic CTFE tracing available on release builds) - #56979 (Adding unwinding support for x86_64_fortanix_unknown_sgx target.) - #56981 (miri: allocation is infallible) - #56984 (A few tweaks to dropck_outlives) - #56989 (Fix compiletest `trim` deprecation warnings) - #56992 (suggest similar lint names for unknown lints) - #57002 (Stabilize Vec(Deque)::resize_with) Failed merges: r? @ghost
bors added a commit
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Dec 21, 2018
Rollup of 20 pull requests Successful merges: - #56802 (Add DoubleEndedIterator::nth_back) - #56842 (Add unstable VecDeque::rotate_{left|right}) - #56869 (Reduce search-index.js size) - #56887 (Disable field reordering for repr(int).) - #56892 (rustc: Update Clang used to build LLVM on Linux) - #56909 (static eval: Do not ICE on layout size overflow) - #56914 (Ignore ui/target-feature-gate on sparc, sparc64, powerpc, powerpc64 and powerpc64le) - #56917 (Simplify MIR generation for logical operations) - #56919 (Remove a wrong multiplier on relocation offset computation) - #56933 (Add --progress to git submodule commands in x.py) - #56941 (deny intra-doc link resolution failures in libstd) - #56964 (Remove `TokenStream::JointTree`.) - #56970 (Mem uninit doc ptr drop) - #56973 (make basic CTFE tracing available on release builds) - #56979 (Adding unwinding support for x86_64_fortanix_unknown_sgx target.) - #56981 (miri: allocation is infallible) - #56984 (A few tweaks to dropck_outlives) - #56989 (Fix compiletest `trim` deprecation warnings) - #56992 (suggest similar lint names for unknown lints) - #57002 (Stabilize Vec(Deque)::resize_with) Failed merges: r? @ghost
Centril added a commit
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Dec 22, 2018
Disable field reordering for repr(int). This fixes the problem that the test in rust-lang#56619 uncovers. Closesrust-lang#56619.
kennytm
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Dec 22, 2018
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@bors p=30 (rollup fairness) |
bors
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Dec 22, 2018
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bors
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Dec 22, 2018
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☀️ Test successful - status-appveyor, status-travis |
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This fixes the problem that the test in #56619 uncovers.
Closes#56619.