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)        
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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