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py/vm.c: Avoid heap-allocating slices for built-ins. - #12518
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Not sure why, but this is failing on unix CI. |
It's failing the "doesn't heap allocate" when using emit-native. Need to add an exclusion for that test when using emit-native. |
Done. |
Codecov ReportAll modified and coverable lines are covered by tests ✅
Additional details and impacted files@@ Coverage Diff @@
## master #12518 +/- ##
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Coverage 98.44% 98.44%
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Files 171 171
Lines 22192 22204 +12
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+ Hits 21847 21859 +12
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I've rebased this on latest master, to see how it goes after ~2 years. |
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This is looking good now. It enables basic slices to work without allocating on the heap, and only increases C stack usage when that feature is used. I think it should be merged. |
This commit adds a fast-path optimisation for when a BUILD_SLICE is immediately followed by a LOAD/STORE_SUBSCR for a native type, to avoid needing to allocate the slice on the heap. In some cases (e.g. `a[1:3] = x`) this can result in no allocations at all. We can't do this for instance types because the get/set/delattr implementation may keep a reference to the slice. Adds more tests to the basic slice tests to ensure that a stack-allocated slice never makes it to Python, and also a heapalloc test that verifies (when using bytecode) that assigning to a slice is no-alloc. This work was funded through GitHub Sponsors. Signed-off-by: Jim Mussared <[email protected]> Signed-off-by: Damien George <[email protected]>
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This is an alternative to #10160 and implements a different variation on @damz's idea. It's still worth considering making the compiler do this (via a new
SLICE_AND_SUBSCRopcode), but this way also has the benefit of handing the is-instance-type check in a simple way.Unlike #10160 though it only helps for bytecode and not the native emitter.
Fast path optimisation for when a BUILD_SLICE is immediately followed by a LOAD/STORE_SUBSCR for a native type to avoid needing to allocate the slice on the heap.
In some cases (e.g.
a[1:3] = x) this can result in no allocations at all.We can't do this for instance types because the get/set/delattr implementation may keep a reference to the slice.
This work was funded through GitHub Sponsors.