perf(allocator/vec): Vec::extend_desugared set len only at end

[overlookmotel]

Improve efficiency of Vec::extend_desugared by setting len only at the end.

std library has to set len on each turn of the loop, because it needs to drop all elements added so far in case of a panic. But our Vec<'a, T> requires that T is not Drop, so we don't have that restriction.

I'm not sure if this will make any difference. Making a PR to see what Codspeed says.

[overlookmotel]

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• perf(allocator/vec): reduce pointer maths in Vec::extend_desugared #11087
• perf(allocator/vec): Vec::extend_desugared set len only at end #11082 👈 (View in Graphite)
• refactor(allocator/vec): access len and cap fields via getters/setters #11081
• refactor(allocator/vec): re-order methods #11080
• perf(allocator/vec): remove SetLenOnDrop #11079
• refactor(allocator/vec): limit scope of #[expect(clippy::cast_possible_truncation)] #11074
• perf(allocator/vec): remove alloc_guard from RawVec::from_raw_parts_in + clarify safety docs #11073
• docs(allocator/vec): correct safety comments for RawVec::append_elements #11072
• refactor(allocator/vec): clarify comment #11071
• main

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[codspeed-hq]

CodSpeed Instrumentation Performance Report

Merging #11082 will not alter performance

_{Comparing 05-16-perf_allocator_vec_vec_extend_desugared_set_len_only_at_end (c325291) with 05-16-refactor_allocator_vec_access_len_and_cap_fields_via_getters_setters (99ad11f)}

Summary

✅ 36 untouched benchmarks