Remove `i586-pc-windows-msvc`

[beetrees]

Proposal

i586-pc-windows-msvc is the non-SSE version of the i686-pc-windows-msvc target, added back in 2016 in rust-lang/rust#32034 when Rust supported Windows XP. Windows XP/Vista support was subsequently dropped in #378, and Windows 7/8 support for then-existing targets was dropped in #651, which raised "the minimum supported Windows version of current targets to Windows 10". i586-pc-windows-msvc is currently listed as a tier 2 target without std support.

Windows hasn't supported pre-SSE2 CPUs since Windows 8, with Windows 7 apparently dropping support for pre-SSE2 CPUs in a March 2018 update. This means that for Windows 10+ the i586-pc-windows-msvc target (when compared to the i686-pc-windows-msvc target) is a footgun: it provides worse performance with more miscompilations (see rust-lang/rust#114479), without providing any greater CPU support, as the underlying OS requires SSE2 anyway.

Given the lack of purpose for this target on Windows 10+ as detailed above the target also fails the tier 2 target policy requirement that a target "must document [...] why the specific difference in baseline expectations provides sufficient value to justify a separate target". There aren't any target maintains listed for this target, and none of the existing Windows 7 maintainers want to maintain a hypothetical i586-win7-windows-msvc target. Therefore, I propose removing the i586-pc-windows-msvc target.

(Previous discussion is available at rust-lang/rust#137244)

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Process

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• File an issue describing the proposal.
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[rustbot]

Important

This issue is not meant to be used for technical discussion. There is a Zulip stream for that. Use this issue to leave procedural comments, such as volunteering to review, indicating that you second the proposal (or third, etc), or raising a concern that you would like to be addressed.

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cc @rust-lang/compiler

[Noratrieb]

@rustbot second

[apiraino]

@rustbot label -final-comment-period +major-change-accepted