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GeezerVison is showing github.com — bpo-43760: Streamline dispatch sequence for machines without computed gotos. by markshannon · Pull Request #25244 · python/cpython

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@markshannon

@markshannon markshannon commented Apr 7, 2021 •
edited by bedevere-bot
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  • Do fetch and decode at end of opocde then jump directly to switch.
    Should allow compilers that don't support computed-gotos, specifically MSVC,
    to generate better code.

  • Cleans up the code

This should have no effect when computed gotos are used.

https://bugs.python.org/issue43760

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@the-knights-who-say-ni the-knights-who-say-ni added the CLA signed label Apr 7, 2021
@bedevere-bot bedevere-bot added the awaiting core review label Apr 7, 2021
@markshannon markshannon added the skip news label Apr 7, 2021
@markshannon

markshannon commented Apr 7, 2021

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Skipping NEWS, as this shouldn't have any noticeable effect. I'll add a NEWS item to the other PR for https://bugs.python.org/issue43760 as that should have a (just?) measurable effect.
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@markshannon
markshannon force-pushed the dispatch-refactor branch 2 times, most recently from feffa76 to d90907f Compare April 7, 2021 11:44
@markshannon
Streamline dispatch sequence for machines without computed gotos.
82d2cd0 
* Do fetch and decode at end of opocde then jump directly to switch.
  Should allow compilers that don't support computed-gotos, specifically MSVC,
  to generate better code.
@markshannon
markshannon force-pushed the dispatch-refactor branch from d90907f to 82d2cd0 Compare April 7, 2021 11:45
@markshannon markshannon added the 🔨 test-with-buildbots Test PR w/ buildbots; report in status section label Apr 7, 2021
@bedevere-bot

bedevere-bot commented Apr 7, 2021

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🤖 New build scheduled with the buildbot fleet by @markshannon for commit 82d2cd0 🤖

If you want to schedule another build, you need to add the ":hammer: test-with-buildbots" label again.
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@bedevere-bot bedevere-bot removed the 🔨 test-with-buildbots Test PR w/ buildbots; report in status section label Apr 7, 2021
@markshannon
Restore stack_pointer before jumping to error handling, in case trace…
860ca09 
… function changed frame *and* raised an exception.
@rhettinger

rhettinger commented Apr 7, 2021

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Thanks for doing this. It looks like a nice improvement.

Why did you switch to uint8_t? That doesn't seem consistent with the rest of the code.
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@markshannon

markshannon commented Apr 8, 2021

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@rhettinger
The primary reason for the change to uint8_t will be in later PR. If we add cases for all unknown opcodes then the compiler will know that the cases are exhaustive and won't need to emit bounds checks when dispatching.
I'll revert it to int for now.
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@markshannon
Clarifications suggested by GvR and R Hettinger.
99a0871
@markshannon markshannon mentioned this pull request Apr 8, 2021
Faster tracing test faster-cpython/cpython#6
Closed
@markshannon
markshannon merged commit 28d28e0 into python:master Apr 8, 2021
@bedevere-bot bedevere-bot removed the awaiting core review label Apr 8, 2021
@markshannon
markshannon deleted the dispatch-refactor branch April 8, 2021 10:43
@neonene neonene mentioned this pull request Sep 29, 2021
bpo-45116 Fix another performance regression on Windows #28630
Closed
@markshannon markshannon mentioned this pull request Sep 13, 2022
The DISPATCH() macro is not as efficient as it could be (move PyThreadState.use_tracing) #87926
Closed
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4 participants

@markshannon @bedevere-bot @rhettinger @the-knights-who-say-ni
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