Store array of original_insns on iseq #5622
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k0kubun
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Mar 4, 2022
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| struct { | ||
| uint8_t *insns; | ||
| unsigned int size; |
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What's different between original_insns.size and iseq_size?
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original_insns.size is the count of instructions in this iseq. iseq_size is the count of instructions + the total count of operands.
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I can't think of a better approach to fix [Bug #18269], so it seems legit to me. |
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This is still an option, but I really don't want to make iseq any larger 😅. I think for now we've worked around the issue in other ways. |
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This aims to fix https://bugs.ruby-lang.org/issues/18269 as well as making GC iseq marking (and anywhere else we iterate through the instructions) faster by avoiding the hash lookup inside
rb_vm_insn_addr2insn.This is done by storing the original instruction values as a byte array on the iseq before they are translated for threading. We can then use those values directly instead of using the hash table from threaded to non-threaded.
The array is per-instruction rather than per-PC-address, so getting the instruction at a specific PC/offset address is awkward and this is designed for iterating the entire iseq. The advantage is that the array is more compact.
The downside of this is that we need to record an extra byte per-vm-instruction.
TODO:
cc @nobu @k0kubun @jeremyevans from linked issue. What do you think of this approach?