avoid shared ref in UnsafeCell::get #56012
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Seems trivially correct to me due to |
nikomatsakis
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@bors r+ |
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I added a comment referring to @bors r=nikomatsakis |
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📌 Commit 25d46f3 has been approved by |
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avoid shared ref in UnsafeCell::get Avoid taking a shared reference in `UnsafeCell::get`. This *should* be taking a raw reference (see rust-lang/rfcs#2582), but that operation is not currently available, so I propose we exploit `repr(transparent)` instead and cast the pointer around. This is required to make `UnsafeCell::get` pass the [stacked borrows implementation](https://www.ralfj.de/blog/2018/11/16/stacked-borrows-implementation.html) in miri (currently, `UnsafeCell::get` is on a whitelist, but that is of course not very satisfying). It shouldn't affect normal execution/codegen. Would be great if we could get this landed and shrink miri's whitelist! Cc @nikomatsakis
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Nov 18, 2018
avoid shared ref in UnsafeCell::get Avoid taking a shared reference in `UnsafeCell::get`. This *should* be taking a raw reference (see rust-lang/rfcs#2582), but that operation is not currently available, so I propose we exploit `repr(transparent)` instead and cast the pointer around. This is required to make `UnsafeCell::get` pass the [stacked borrows implementation](https://www.ralfj.de/blog/2018/11/16/stacked-borrows-implementation.html) in miri (currently, `UnsafeCell::get` is on a whitelist, but that is of course not very satisfying). It shouldn't affect normal execution/codegen. Would be great if we could get this landed and shrink miri's whitelist! Cc @nikomatsakis
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Nov 19, 2018
Rollup of 25 pull requests Successful merges: - #55562 (Add powerpc- and powerpc64-unknown-linux-musl targets) - #55564 (test/linkage-visibility: Ignore on musl targets) - #55827 (A few tweaks to iterations/collecting) - #55834 (Forward the ABI of the non-zero sized fields of an union if they have the same ABI) - #55857 (remove unused dependency) - #55862 (in which the E0618 "expected function" diagnostic gets a makeover) - #55867 (do not panic just because cargo failed) - #55894 (miri enum discriminant handling: Fix treatment of pointers, better error when it is undef) - #55916 (Make miri value visitor usfeful for mutation) - #55919 (core/tests/num: Simplify `test_int_from_str_overflow()` test code) - #55923 (reword #[test] attribute error on fn items) - #55935 (appveyor: Use VS2017 for all our images) - #55949 (ty: return impl Iterator from Predicate::walk_tys) - #55952 (Update to Clang 7 on CI.) - #55953 (#53488 Refactoring UpvarId) - #55962 (rustdoc: properly calculate spans for intra-doc link resolution errors) - #55963 (Stress test for MPSC) - #55968 (Clean up some non-mod-rs stuff.) - #55970 (Miri backtrace improvements) - #56007 (CTFE: dynamically make sure we do not call non-const-fn) - #56011 (Replace data.clone() by Arc::clone(&data) in mutex doc.) - #56012 (avoid shared ref in UnsafeCell::get) - #56016 (Add VecDeque::resize_with) - #56027 (docs: Add missing backtick in object_safety.rs docs) - #56043 (remove "approx env bounds" if we already know from trait) Failed merges: r? @ghost
kennytm
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Nov 19, 2018
avoid shared ref in UnsafeCell::get Avoid taking a shared reference in `UnsafeCell::get`. This *should* be taking a raw reference (see rust-lang/rfcs#2582), but that operation is not currently available, so I propose we exploit `repr(transparent)` instead and cast the pointer around. This is required to make `UnsafeCell::get` pass the [stacked borrows implementation](https://www.ralfj.de/blog/2018/11/16/stacked-borrows-implementation.html) in miri (currently, `UnsafeCell::get` is on a whitelist, but that is of course not very satisfying). It shouldn't affect normal execution/codegen. Would be great if we could get this landed and shrink miri's whitelist! Cc @nikomatsakis
bors
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Nov 19, 2018
Rollup of 25 pull requests Successful merges: - #55562 (Add powerpc- and powerpc64-unknown-linux-musl targets) - #55564 (test/linkage-visibility: Ignore on musl targets) - #55827 (A few tweaks to iterations/collecting) - #55834 (Forward the ABI of the non-zero sized fields of an union if they have the same ABI) - #55857 (remove unused dependency) - #55862 (in which the E0618 "expected function" diagnostic gets a makeover) - #55867 (do not panic just because cargo failed) - #55894 (miri enum discriminant handling: Fix treatment of pointers, better error when it is undef) - #55916 (Make miri value visitor useful for mutation) - #55919 (core/tests/num: Simplify `test_int_from_str_overflow()` test code) - #55923 (reword #[test] attribute error on fn items) - #55949 (ty: return impl Iterator from Predicate::walk_tys) - #55952 (Update to Clang 7 on CI.) - #55953 (#53488 Refactoring UpvarId) - #55962 (rustdoc: properly calculate spans for intra-doc link resolution errors) - #55963 (Stress test for MPSC) - #55968 (Clean up some non-mod-rs stuff.) - #55970 (Miri backtrace improvements) - #56007 (CTFE: dynamically make sure we do not call non-const-fn) - #56011 (Replace data.clone() by Arc::clone(&data) in mutex doc.) - #56012 (avoid shared ref in UnsafeCell::get) - #56016 (Add VecDeque::resize_with) - #56027 (docs: Add missing backtick in object_safety.rs docs) - #56043 (remove "approx env bounds" if we already know from trait) - #56059 (Increase `Duration` approximate equal threshold to 1us)
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Avoid taking a shared reference in
UnsafeCell::get. This should be taking a raw reference (see rust-lang/rfcs#2582), but that operation is not currently available, so I propose we exploitrepr(transparent)instead and cast the pointer around.This is required to make
UnsafeCell::getpass the stacked borrows implementation in miri (currently,UnsafeCell::getis on a whitelist, but that is of course not very satisfying). It shouldn't affect normal execution/codegen. Would be great if we could get this landed and shrink miri's whitelist!Cc @nikomatsakis