rustc_trans: don't apply noalias on returned references.#46253
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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.
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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.