[New-bugs-announce] [issue26802] Avoid copy in call_function_var when no extra stack args are passed

[Joe Jevnik]

New submission from Joe Jevnik:

When star unpacking positions into a function we can avoid a copy iff there are no extra arguments coming from the stack. Syntactically this looks like: `f(*args)`

This reduces the overhead of the call by about 25% (~30ns on my machine) based on some light profiling of just * unpacking. I can imagine this having a slight impact on code that uses this feature in a loop.

The cost is minimal when we need to make the copy because the int != 0 check is dwarfed by the allocation. I did not notice a significant change between the slow path and the original code.

The macro benchmark suite did not show a difference on my machine but this is not much more complex code.

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components: Interpreter Core
files: call-function-var.patch
keywords: patch
messages: 263702
nosy: llllllllll
priority: normal
severity: normal
status: open
title: Avoid copy in call_function_var when no extra stack args are passed
versions: Python 3.6
Added file: http://bugs.python.org/file42512/call-function-var.patch

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue26802>
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