gh-131798: Add tier-2 list specialization for STORE_SLICE#149446
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eendebakpt wants to merge 10 commits into
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gh-131798: Add tier-2 list specialization for STORE_SLICE#149446eendebakpt wants to merge 10 commits into
eendebakpt wants to merge 10 commits into
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Adds a tier-2 only `_STORE_SLICE_LIST` op and a guard `_GUARD_THIRD_LIST`, plus an optimizer rule that rewrites generic `_STORE_SLICE` to the list fast path when the LHS container is (or can be guarded as) an exact list. The list path calls a new `_PyList_StoreSlice` helper that adjusts the slice indices and dispatches into `list_ass_slice_lock_held` directly, skipping the slice-object allocation and the generic `PyObject_SetItem` lookup. The tier-1 `_STORE_SLICE` opcode is left unchanged so non-list callers incur no extra branch. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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eendebakpt
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Resolved generated pycore_uop_ids.h conflict by regenerating from bytecodes.c / optimizer_bytecodes.c. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
markshannon
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May 22, 2026
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One question, otherwise looks good.
It would be good to optimize constant slices, but that would need a change to the bytecode compiler. For another PR.
eendebakpt
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May 22, 2026
Picks up the dead-local removal from the latest commit
('Apply suggestion from @eendebakpt') in optimizer_bytecodes.c.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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The JIT currently dispatches
STORE_SLICE(container[start:stop] = value) throughPyObject_SetItemeven when the trace has proven the container is an exact list. Adding a tier-2 specialization_STORE_SLICE_LISTskips the slice-object allocation and the generic lookup.The optimizer rewrites
_STORE_SLICE→_STORE_SLICE_LISTonly when the container's type is statically known, so non-list callers and tier-1 are unaffected. A second commit forbytearraywas added but reverted.Benchmark results on pyperformance
fannkuch(tier-2 / JIT enabled):