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Use zeroed allocations in the mir interpreter instead eagerly touching the memor...
source link: https://github.com/rust-lang/rust/pull/87777
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#86255 introduced a 30% regression in page faults and a 3% regression in max-rss in the ctfe-stress benchmarks.
That's most likely happened because it separated allocation from initialization of the vec which defeats the zero-optimization.
Currently there's no allocation API that is fallible, zeroing and returns a slice, so this PR introduces one and then uses that to solve the problem. In principle vec.resize(len, 0) could be optimized to use alloc::grow_zeroed where appropriate but that would require new specializations and new plumbing in RawVec.
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