Optimize compilation of large literal arrays #9721
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To avoid stack overflow, Ruby splits compilation of large arrays
into smaller arrays, and concatenates the small arrays together.
It previously used newarray/concatarray for this, which is
inefficient. This switches the compilation to use pushtoarray,
which is much faster. This makes almost all literal arrays only
allocate a single array.
For cases where there is a large amount of static values in the
array, Ruby will statically compile subarrays, and previously
added them using concatarray. This switches to concattoarray,
avoiding an array allocation for the append.
Keyword splats are also supported in arrays, and ignored if the
keyword splat is empty. Previously, this used newarraykwsplat and
concatarray. This still uses newarraykwsplat, but switches to
concattoarray to save an allocation. So large arrays with keyword
splats can allocate 2 arrays instead of 1.
Previously, for the following array sizes (assuming local variable
access for each element), Ruby allocated the following number of
arrays:
1000 elements: 7 arrays
10000 elements: 79 arrays
100000 elements: 781 arrays
With these changes, only a single array is allocated (or 2 for a
large array with a keyword splat.
Results using the included benchmark:
```
array_1000
miniruby: 34770.0 i/s
./miniruby-before: 10511.7 i/s - 3.31x slower
array_10000
miniruby: 4938.8 i/s
./miniruby-before: 483.8 i/s - 10.21x slower
array_100000
miniruby: 727.2 i/s
./miniruby-before: 4.1 i/s - 176.98x slower
```
jeremyevans
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Jan 26, 2024
Previously, a literal array with a splat and any other args resulted in more than one array allocation: ```ruby [1, *a] [*a, 1] [*a, *a] [*a, 1, 2] [*a, a] [*a, 1, *a] [*a, 1, a] [*a, a, a] [*a, a, *a] [*a, 1, *a, 1] [*a, 1, *a, *a] [*a, a, *a, a] ``` This is because previously Ruby would use newarray and concatarray to create the array, which both each allocate an array internally. This changes the compilation to use concattoarray and pushtoarray, which do not allocate arrays. It also updates the peephole optimizer to optimize the duparray/concattoarray sequence to putobject/concattoarray, mirroring the existing duparray/concatarray optimization. These changes reduce the array allocations for the above examples to a single array allocation, except for: ``` [*a, 1, a] [*a, a, a] ``` The reason for this is because optimizing this case to only allocate 1 array requires changes to compile_array, which would currently conflict with an unmerged pull request (ruby#9721). After that pull request is merged, it should be possible to refactor things to only allocate a 1 array for all literal arrays (or 2 for arrays with keyword splats).
nobu
reviewed
Jan 27, 2024
nobu
approved these changes
Jan 27, 2024
Co-authored-by: Nobuyoshi Nakada <nobu@ruby-lang.org>
jeremyevans
added a commit
that referenced
this pull request
Jan 27, 2024
Previously, a literal array with a splat and any other args resulted in more than one array allocation: ```ruby [1, *a] [*a, 1] [*a, *a] [*a, 1, 2] [*a, a] [*a, 1, *a] [*a, 1, a] [*a, a, a] [*a, a, *a] [*a, 1, *a, 1] [*a, 1, *a, *a] [*a, a, *a, a] ``` This is because previously Ruby would use newarray and concatarray to create the array, which both each allocate an array internally. This changes the compilation to use concattoarray and pushtoarray, which do not allocate arrays. It also updates the peephole optimizer to optimize the duparray/concattoarray sequence to putobject/concattoarray, mirroring the existing duparray/concatarray optimization. These changes reduce the array allocations for the above examples to a single array allocation, except for: ``` [*a, 1, a] [*a, a, a] ``` The reason for this is because optimizing this case to only allocate 1 array requires changes to compile_array, which would currently conflict with an unmerged pull request (#9721). After that pull request is merged, it should be possible to refactor things to only allocate a 1 array for all literal arrays (or 2 for arrays with keyword splats).
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To avoid stack overflow, Ruby splits compilation of large arrays into smaller arrays, and concatenates the small arrays together. It previously used newarray/concatarray for this, which is inefficient. This switches the compilation to use pushtoarray, which is much faster. This makes almost all literal arrays only allocate a single array.
For cases where there is a large amount of static values in the array, Ruby will statically compile subarrays, and previously added them using concatarray. This switches to concattoarray, avoiding an array allocation for the append.
Keyword splats are also supported in arrays, and ignored if the keyword splat is empty. Previously, this used newarraykwsplat and concatarray. This still uses newarraykwsplat, but switches to concattoarray to save an allocation. So large arrays with keyword splats can allocate 2 arrays instead of 1.
Previously, for the following array sizes (assuming local variable access for each element), Ruby allocated the following number of arrays:
1000 elements: 7 arrays
10000 elements: 79 arrays
100000 elements: 781 arrays
With these changes, only a single array is allocated (or 2 for a large array with a keyword splat.
Results using the included benchmark: