Make length/1 yielding #2053
Make length/1 yielding #2053
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bjorng
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| gc_bif1 Fail=j Live u$bif:erlang:length/1 Src Dst => \ | ||
| i_length_setup Live Src | i_length Fail Live Dst | ||
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| i_length_setup t x |
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Would using i_length_setup t xyc work in here?
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Additionally, given i_length_setup is so tiny - would it make sense to also define it for r? It shouldn't grow the main loop significantly, but might save some space in the bytecode.
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Would using i_length_setup t xyc work in here?
Yes, it would. Fixed.
Additionally, given i_length_setup is so tiny - would it make sense to also define it for r? It shouldn't grow the main loop significantly, but might save some space in the bytecode.
That would not save any BEAM code space, as the t and x operands are packed into the same 32-bit word. It could possibly save a tiny, tiny amount of execution time, but not enough to make it worthwhile.
While looking at the generated code, I realized that I had forgotten to implement a minor optimization that I had thought of earlier.
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The guard BIF `length/1` would calculate the length of the list in one go without yielding, even if the list was were long. To make it even worse, the call to `length/1` would only cost a single reduction. This commit reimplements `length/1` so that it eats a number of reductions proportional to the length of the list, and yields if the available reductions run out.
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The guard BIF
length/1would calculate the length of the list in onego without yielding, even if the list was were long. To make it even
worse, the call to
length/1would only cost a single reduction.This commit reimplements
length/1so that it eats a number ofreductions proportional to the length of the list, and yields if the
available reductions run out.