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Reorder mir_const_qualif to make promotion in consts more consistent #65883

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Reorder mir_const_qualif to make promotion in consts more consistent #65883

wants to merge 4 commits into from

Commits on Oct 28, 2019

  1. Swap order of mir_const_qualif and mir_validated 

    Computing `mir_const_qualif` requires running
`QualifyAndPromoteConstants`, but no promotion was actually done until
`mir_validated`. This required persisting a `BitSet` of promoted locals
across queries, making it difficult to properly handle promotion in
`const`s.

This commit swaps the order of the two queries, and stores the result of
`mir_const_qualif` (a single `u8`) in the result of `mir_validated`.
`mir_const_qualif` now simply invokes `mir_validated` and extracts this
result.
    @ecstatic-morse
    ecstatic-morse committed Oct 28, 2019
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  2. Bless cycle tests with extra step

    @ecstatic-morse
    ecstatic-morse committed Oct 28, 2019
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  3. Don't check new promotion logic in consts if CFG is complex 

    The old promotion logic ignores anything after a branch or loop in a
`const`, so the new logic will often find new things to promote. Note
that we can't actually do promotion in a `const` within a loop body
using the current approach of removing `Drop` and `StorageDead`.
    @ecstatic-morse
    ecstatic-morse committed Oct 28, 2019
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  4. Don't change for promotable array initializers in const to Copy

    @ecstatic-morse
    ecstatic-morse committed Oct 28, 2019
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