GH-130415: Use boolean guards to narrow types to values in the JIT

[brandtbucher]

This adds a symbolic "truth" type to the JIT optimizer, allowing tests like if not x: ... to narrow the value of x based on its type. Currently, it's only implemented for booleans, but I'm working with a few people to open PRs to narrow int and str values as well.

(The diff looks much worse than it is, since this requires adding ctx parameters to a couple of helper functions that are used everywhere. The "real" changes in optimizer_bytecodes.c are limited to _GUARD_IS_FALSE_POP, _GUARD_IS_NONE_POP, _GUARD_IS_TRUE_POP, _TO_BOOL, _TO_BOOL_BOOL, and _UNARY_NOT.

• Issue: Better constant narrowing in the JIT optimizer #130415

[markshannon]

Looks correct, but I'm not keen on the names. Naming is hard, so I don't have much better names.

At least "truthy", rather than just "truth", would suggest Python bool(x) semantics.
Maybe "to_bool"?

Also, can you add some C tests to Python/optimizer_symbols.c for the various operations?

[markshannon]

From casual reading, this looks like an error as the true argument implies that this has the value True.

Maybe rename sym_new_truth as sym_from_truthiness and have false as the argument for NOT and true as the argument for TO_BOOL?

[markshannon]

Or symbolic consts, like TO_BOOL and INVERT?

[brandtbucher]

I'd like to avoid a double-negative in the arg name (since inverting it from its current meaning would mean something like "not not"). What if I make it an int and use 0 and 1 instead? I feel like a big part of the friction in reading this is the use of true and false as arguments.

[markshannon]

0 /1 or false/true doesn't matter. Good symbolic names is what is needed.
Maybe even use two different functions with different names?

[brandtbucher]

I agree the naming is hard. How about JitSymbolBoolOf and sym_new_bool_of? I feel like "truthy" implies that the value can't be falsey ("truth" is a noun, "truthy" is an adjective describing a value's truth).

[brandtbucher]

We can think ahead with the naming too. Soon we’ll have equality and identity as symbols, and we’ll probably want something reasonably consistent (“truth”, “equality”, and “identity” were the planned names).

[markshannon]

"truthy" is an adjective describing a value's truth

Maybe "truthiness" rather than "truthy" then?

[markshannon]

I've heard "truthiness" used to describe the boolean value of a non-boolean in a test. Probably more in a javascript context, but for Python as well.

[brandtbucher]

Sounds good, thanks for the suggestions.

[bedevere-bot]

⚠️⚠️⚠️ Buildbot failure ⚠️⚠️⚠️

Hi! The buildbot AMD64 CentOS9 NoGIL Refleaks 3.x (tier-1) has failed when building commit 7afa476.

What do you need to do:

1. Don't panic.
2. Check the buildbot page in the devguide if you don't know what the buildbots are or how they work.
3. Go to the page of the buildbot that failed (https://buildbot.python.org/#/builders/1610/builds/946) and take a look at the build logs.
4. Check if the failure is related to this commit (7afa476) or if it is a false positive.
5. If the failure is related to this commit, please, reflect that on the issue and make a new Pull Request with a fix.

You can take a look at the buildbot page here:

https://buildbot.python.org/#/builders/1610/builds/946

Failed tests:

• test_free_threading

Summary of the results of the build (if available):

==

Click to see traceback logs

remote: Enumerating objects: 19, done. remote: Counting objects: 7% (1/14) remote: Counting objects: 14% (2/14) remote: Counting objects: 21% (3/14) remote: Counting objects: 28% (4/14) remote: Counting objects: 35% (5/14) remote: Counting objects: 42% (6/14) remote: Counting objects: 50% (7/14) remote: Counting objects: 57% (8/14) remote: Counting objects: 64% (9/14) remote: Counting objects: 71% (10/14) remote: Counting objects: 78% (11/14) remote: Counting objects: 85% (12/14) remote: Counting objects: 92% (13/14) remote: Counting objects: 100% (14/14) remote: Counting objects: 100% (14/14), done. remote: Compressing objects: 9% (1/11) remote: Compressing objects: 18% (2/11) remote: Compressing objects: 27% (3/11) remote: Compressing objects: 36% (4/11) remote: Compressing objects: 45% (5/11) remote: Compressing objects: 54% (6/11) remote: Compressing objects: 63% (7/11) remote: Compressing objects: 72% (8/11) remote: Compressing objects: 81% (9/11) remote: Compressing objects: 90% (10/11) remote: Compressing objects: 100% (11/11) remote: Compressing objects: 100% (11/11), done. remote: Total 19 (delta 3), reused 3 (delta 3), pack-reused 5 (from 1)  From https://github.com/python/cpython * branch main -> FETCH_HEAD Note: switching to '7afa476874b9a432ad6dbe9fb3e65d62f2999f88'. You are in 'detached HEAD' state. You can look around, make experimental changes and commit them, and you can discard any commits you make in this state without impacting any branches by switching back to a branch. If you want to create a new branch to retain commits you create, you may do so (now or later) by using -c with the switch command. Example: git switch -c <new-branch-name> Or undo this operation with: git switch - Turn off this advice by setting config variable advice.detachedHead to false HEAD is now at 7afa476874b GH-130415: Use boolean guards to narrow types to values in the JIT (GH-130659) Switched to and reset branch 'main' configure: WARNING: no system libmpdecimal found; falling back to bundled libmpdecimal (deprecated and scheduled for removal in Python 3.15)make: *** [Makefile:2325: buildbottest] Error 2