GH-127953: Make line number lookup O(1) regardless of the size of the code object #128350
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markshannon
added
needs backport to 3.12
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Benchmarking shows no significant change in performance. The coverage benchmark shows a small speedup, but it is probably noise. |
| return COMPUTED_LINE; | ||
| int delta = line - code->co_firstlineno; | ||
| assert(delta > NO_LINE); | ||
| return delta; |
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Looks like line_delta is actually an offset from the start now.
| get_line_delta(_PyCoLineInstrumentationData *line_data, int index) | ||
| { | ||
| uint8_t *ptr = &line_data->data[index*line_data->bytes_per_entry+1]; | ||
| uint32_t value = *ptr; |
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Could assert here that bytes_per_entry is within range.
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We can't easily assert anything here, as we don't know the max line number without traversing the entire locations table.
I've added an assert to set_line_delta instead.
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I meant that bytes_per_entry is between 1 and 4.
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(bytes_per_entry is between 2 and 5 because it includes the original opcode)
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I’m taking a vacation now and I’ll take a look once I’m back! |
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Thanks @markshannon for the PR 🌮🎉.. I'm working now to backport this PR to: 3.12, 3.13. |
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Sorry, @markshannon, I could not cleanly backport this to |
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Sorry, @markshannon, I could not cleanly backport this to |
…of the code object (pythonGH-128350)
…e size of the code object (python#129127) pythonGH-127953: Make line number lookup O(1) regardless of the size of the code object (pythonGH-128350)
Changes the line data array from 2 bytes per instruction to 2-5 bytes per instruction depending on the line length of the code object, changing the size of the line delta from 1 byte to 1-4 bytes as needed.
Most code objects are fewer than 250 lines, and still use 1 byte for line delta per instruction.
Code objects up to ~65k lines need 2 bytes per instruction.
3 bytes are needed for code objects up to ~16M lines long.
4 bytes are needed for code objects up to the maximum of ~1 billion lines.
I doubt 4 bytes will ever be needed, but it is supported.
This PR also fixes the
INSTRUMENT_DEBUGmode which was broken in 2e95c5bThe time taken to execute the example given in #127953 (comment) is about the same as 3.10 or 3.11. Maybe a bit faster, but I didn't benchmark it rigorously.
Modifying the script to generate a file of 100k lines, this PR is a bit faster than 3.11.
At 1M lines, this PR is a bit slower than 3.11.