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2025-07-16py/vm: Avoid heap-allocating slices when subscripting built-ins.Jim Mussared
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 <jim.mussared@gmail.com> Signed-off-by: Damien George <damien@micropython.org>