Don't restack if pointer-free

[tkf]

No description provided.

[codecov]

Codecov Report

Merging #504 (4543026) into master (3f52fa9) will increase coverage by 0.04%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #504      +/-   ##
==========================================
+ Coverage   93.41%   93.45%   +0.04%     
==========================================
  Files          32       32              
  Lines        2217     2217              
==========================================
+ Hits         2071     2072       +1     
+ Misses        146      145       -1     

Flag	Coverage Δ
Pkg.test	89.62% <100.00%> (+0.04%)	⬆️
Run.test	93.27% <100.00%> (ø)

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Impacted Files	Coverage Δ
src/AutoObjectsReStacker.jl	95.65% <100.00%> (ø)
src/nondeterministic_threading.jl	89.79% <0.00%> (+1.02%)	⬆️

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[tkf]

It looks like restack still matters for pointer-free types https://github.com/JuliaFolds/Transducers-data/blob/multi-thread-benchmark-results/2022/01/29/054144/result.md

ID	time ratio	memory ratio
...	...	...
["partition_length_maximum", "rand", "reduce"]	5.07 (5%) ❌	1.00 (1%)

See also:

• [NOTE] Effect of restack on ReducePartitionBy performance #459
• Add ReducePartitionBy #458