René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Better constant narrowing in the JIT optimizer","articleBody":"**Please don't work on this. I'm planning on sprinting on this with new contributors at an event this weekend.**\n\nCurrently, the JIT optimizer uses the `_COMPARE_OP` family, `_CONTAINS_OP`, `_IS_OP`, and the `_TO_BOOL` family to narrow the *types* of the input values and the type of the output value.\n\nHowever, by \"peeking ahead\" and seeing how a value will be used, we can narrow these types to constants as well. As a simple example, consider `_TO_BOOL_INT + _GUARD_IS_FALSE_CHECK` on an unknown value. After the `_TO_BOOL_INT`, it can be narrowed to a known class, `int` (we do this today). However, after the `_GUARD_IS_FALSE_CHECK`, we can actually narrow it to a constant value, `0`.\n\nAn example implementation of this idea for `_TO_BOOL_BOOL` is here: https://github.com/python/cpython/compare/main...brandtbucher:cpython:hack-night-to-bool-bool\n \nI've divided this work into 3 \"waves\" of increasing complexity. Tasks in **bold** are probably a bit harder, tasks in *italics* are probably a bit easier.\n\n## Narrow types to constants in branches involving truthiness:\n\n- [x] **`_TO_BOOL + _GUARD_IS_*_POP`** [gh-130659](https://github.com/python/cpython/pull/130659)\n- [x] *`_TO_BOOL_BOOL + _GUARD_IS_*_POP`* [gh-130659](https://github.com/python/cpython/pull/130659)\n- [x] `_TO_BOOL_INT + _GUARD_IS_*_POP` [gh-130772](https://github.com/python/cpython/pull/130772)\n- [ ] ~**`_TO_BOOL_LIST + _GUARD_IS_*_POP`**~\n- [x] `_TO_BOOL_STR + _GUARD_IS_*_POP` [gh-130476](https://github.com/python/cpython/pull/130476)\n\n## Narrow types to constants in branches involving comparisons with a constant:\n\n- [ ] **`_COMPARE_OP + _GUARD_IS_*_POP` (`==`, `!=`)**\n- [ ] `_COMPARE_OP_FLOAT + _GUARD_IS_*_POP` (`==`, `!=`)\n- [ ] `_COMPARE_OP_INT + _GUARD_IS_*_POP` (`==`, `!=`)\n- [ ] `_COMPARE_OP_STR + _GUARD_IS_*_POP` (`==`, `!=`)\n- [ ] **`_CONTAINS_OP + _GUARD_IS_*_POP` (`in`, `not in`)**\n- [ ] *`_IS_OP + _GUARD_IS_*_POP` (`is`, `is not`)*\n\n## Evaluate comparisons involving two constants:\n\nThis is related, but a bit more involved, since we need a way to pop two values from the stack and push a constant (`_POP_TWO_LOAD_CONST_INLINE_BORROW`). We should also teach `remove_unneeded_uops` about this new instruction.\n\n- [x] **`_COMPARE_OP`** (`==`, `!=`, `\u003c`, `\u003e`, `\u003c=`, `\u003e=`)\n- [x] `_COMPARE_OP_FLOAT` (`==`, `!=`, `\u003c`, `\u003e`, `\u003c=`, `\u003e=`) [gh-137062](https://github.com/python/cpython/pull/137062)\n- [x] `_COMPARE_OP_INT` (`==`, `!=`, `\u003c`, `\u003e`, `\u003c=`, `\u003e=`) [gh-131489](https://github.com/python/cpython/pull/131489) \n- [x] `_COMPARE_OP_STR` (`==`, `!=`, `\u003c`, `\u003e`, `\u003c=`, `\u003e=`) [gh-137062](https://github.com/python/cpython/pull/137062)\n- [x] **`_CONTAINS_OP` (`in`, `not in`)**\n- [ ] ~*`_IS_OP` (`is`, `is not`)*~\n\n\u003c!-- gh-linked-prs --\u003e\n### Linked PRs\n* gh-130476\n* gh-130477\n* gh-130659\n* gh-130772\n* gh-131489\n* gh-131778\n* gh-132333\n* gh-132708\n* gh-134241\n* gh-137062\n* gh-143895\n\u003c!-- /gh-linked-prs --\u003e\n","author":{"url":"https://github.com/brandtbucher","@type":"Person","name":"brandtbucher"},"datePublished":"2025-02-21T17:23:01.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":16},"url":"https://github.com/130415/cpython/issues/130415"}