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rustc_trans: don't apply noalias on returned references. - #46253
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rust-highfive
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Nov 25, 2017
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(rust_highfive has picked a reviewer for you, use r? to override) |
nagisa
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Nov 25, 2017
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@bors r+ |
bors
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Nov 25, 2017
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📌 Commit 5eed95e has been approved by |
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bors
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Nov 26, 2017
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Nov 26, 2017
rustc_trans: don't apply noalias on returned references. In #45225 frozen returned `&T` were accidentally maked `noalias`, unlike `&mut T`. Return value `noalias` is only sound for functions that return dynamic allocations, e.g. `Box`, and using it on anything else can lead to miscompilation, as LLVM assumes certain usage patterns. Fixes#46239.
bors
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Nov 26, 2017
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☀️ Test successful - status-appveyor, status-travis |
michaelwoerister
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Dec 4, 2017
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As per the IRC discussion with @eddyb on Friday, I'll tentatively mark this as beta-accepted. @rust-lang/compiler, please veto within the next 15 hours if you don't think this is a good idea. I'll do the backport tomorrow. |
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In #45225 frozen returned
&Twere accidentally makednoalias, unlike&mut T.Return value
noaliasis only sound for functions that return dynamic allocations, e.g.Box, and using it on anything else can lead to miscompilation, as LLVM assumes certain usage patterns.Fixes#46239.