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Avoid copying some undef memory in MIR #62655

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Closed

Avoid copying some undef memory in MIR #62655

wants to merge 2 commits into from
+27 −24

Commits on Dec 2, 2019

  1. Avoid copying memory representation of undef data 

    During MIR interpretation it may happen that a place containing
uninitialized bytes is copied. This would read the current
representation of these bytes and write it to the destination even
though they must, by definition, not matter to the execution.

This elides that representation change when no bytes are defined in such
a copy, saving some cpu cycles. In such a case, the memory of the target
allocation is not touched at all which also means that sometimes no
physical page backing the memory allocation of the representation needs
to be provided by the OS at all, reducing memory pressure on the system.
    @HeroicKatora
    HeroicKatora committed Dec 2, 2019
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  2. Remove obsolete uninit mention from impl comment

    @HeroicKatora
    HeroicKatora committed Dec 2, 2019
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