bpo-46841: Use inline caching for attribute accesses#31640
Merged
Uh oh!
There was an error while loading. Please reload this page.
Conversation
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters. Learn more about bidirectional Unicode characters
brandtbucher commented Mar 2, 2022
Python/ceval.c Outdated
Comment on lines 1462 to 1463
| /* XXX: Remove this next line to make test_asyncio very angry! */ \ | ||
| DEOPT_IF(LOAD_##attr_or_method == LOAD_ATTR, LOAD_##attr_or_method); \ |
MemberAuthor
There was a problem hiding this comment.
All tests pass if we deopt every LOAD_ATTR_MODULE right here. Removing this line activates some very strange failures!
Member
There was a problem hiding this comment.
Casting a _PyLoadMethodCache to a _PyAttrCache may not be valid.
MemberAuthor
brandtbucher commented Mar 2, 2022
(We're also going to want to hit this with the buildbots once it's working.) |
markshannon requested changes Mar 2, 2022
Member
markshannon left a comment
markshannon left a comment There was a problem hiding this comment.
I like the change to use arrays in the structs. It's much clearer that my _m1 field.
But, be careful of casting one struct to another, and be aware that the C compiler treats arrays as simple pointers.
Uh oh!
There was an error while loading. Please reload this page.
Uh oh!
There was an error while loading. Please reload this page.
Uh oh!
There was an error while loading. Please reload this page.
| def_op('BUILD_SET', 104) # Number of set items | ||
| def_op('BUILD_MAP', 105) # Number of dict entries | ||
| name_op('LOAD_ATTR', 106) # Index in name list | ||
| name_op('LOAD_ATTR', 106, 4) # Index in name list |
Member
There was a problem hiding this comment.
The existence of the LOAD_MODULE_ATTR_OR_METHOD macro implies that the LOAD_ATTR and LOAD_METHOD caches should have the same layout. Yet, this has size 4 and LOAD_METHOD has size 10.
This may be the source of your problem.
Are you using the two version numbers consistently?
| _Py_CODEUNIT dict_offset; | ||
| _Py_CODEUNIT keys_version[2]; | ||
| _Py_CODEUNIT descr[4]; | ||
| } _PyLoadMethodCache; |
Member
There was a problem hiding this comment.
Given that LOAD_METHOD_MODULE and LOAD_ATTR_MODULE share code, maybe change this to:
typedef struct{_PyAttrCache attr; _Py_CODEUNIT keys_version[2]; _Py_CODEUNIT descr[4]} _PyLoadMethodCache; MemberAuthor
There was a problem hiding this comment.
I'd rather leave it as-is. Otherwise, accessing the attr methods, including the counter, is a bit awkward.
In response to your other comments: I don't think we're doing anything illegal here, since we only use one consistent cache layout for each specialized form (meaning, _PyLoadMethodCache and _AttrCache members never alias each other). The exception is the counter member for all instructions, but C guarantees that it the first member of a struct will always be at offset 0. So no issues there.
Python/ceval.c Outdated
Comment on lines 1462 to 1463
| /* XXX: Remove this next line to make test_asyncio very angry! */ \ | ||
| DEOPT_IF(LOAD_##attr_or_method == LOAD_ATTR, LOAD_##attr_or_method); \ |
Member
There was a problem hiding this comment.
Casting a _PyLoadMethodCache to a _PyAttrCache may not be valid.
bedevere-bot commented Mar 2, 2022
When you're done making the requested changes, leave the comment: |
26 tasks
MemberAuthor
Okay, that was officially the wildest bug I've ever dealt with. The problematic bytecode sequence (buried deep in Quickened: After specializating the first Finally, after specializing the second Did you catch that? The cached index was turned into a The code that did that is here. Basically, the low byte of the cached index just happened to be What it really did, though, was change the module attribute cached index from Phew. |
MemberAuthor
brandtbucher commented Mar 2, 2022
This whole incident highlights one limitation with the new inline caching approach: it's no longer safe to peek backwards at previous instructions, since you might actually be looking into a cache entry instead. I don't see how we can keep I'll also go over the existing specialization code and see if we're doing this anywhere else. |
MemberAuthor
brandtbucher commented Mar 2, 2022
It also highlights the need for a |
MemberAuthor
brandtbucher commented Mar 2, 2022
Looping in @sweeneyde, since I might need to get rid of |
Member
sweeneyde commented Mar 3, 2022
I didn't see the macro benchmark needle move too much when it was added, so if it's architecturally necessary to, I have no problem with it being scrapped for now. |
brandtbucher added awaiting change review and removed DO-NOT-MERGE awaiting changes labels brandtbucher added the 🔨 test-with-buildbots bedevere-bot commented Mar 3, 2022
🤖 New build scheduled with the buildbot fleet by @brandtbucher for commit 452c78c 🤖 If you want to schedule another build, you need to add the ":hammer: test-with-buildbots" label again. |
bedevere-bot removed the 🔨 test-with-buildbots MemberAuthor
Buildbot failures look unrelated. |
| return-1; | ||
| } | ||
| if (err){ | ||
| if (_Py_OPCODE(instr[0]) ==LOAD_ATTR_INSTANCE_VALUE){ |
Member
There was a problem hiding this comment.
This is a common pair and it saves a POP/PUSH pair and an incref/decref pair, so I'd like to revisit this in the future.
Do we have an issue for that?
MemberAuthor
There was a problem hiding this comment.
Discussion: faster-cpython/ideas#291
Issue: https://bugs.python.org/issue46823
Merged
Sign up for freeto join this conversation on GitHub. Already have an account? Sign in to comment
5 participants
Add this suggestion to a batch that can be applied as a single commit.This suggestion is invalid because no changes were made to the code.Suggestions cannot be applied while the pull request is closed.Suggestions cannot be applied while viewing a subset of changes.Only one suggestion per line can be applied in a batch.Add this suggestion to a batch that can be applied as a single commit.Applying suggestions on deleted lines is not supported.You must change the existing code in this line in order to create a valid suggestion.Outdated suggestions cannot be applied.This suggestion has been applied or marked resolved.Suggestions cannot be applied from pending reviews.Suggestions cannot be applied on multi-line comments.Suggestions cannot be applied while the pull request is queued to merge.Suggestion cannot be applied right now. Please check back later.
CC @markshannon. These three share a lot of code, so it makes sense to convert them together.
Marking asDO-NOT-MERGEsinceLOAD_ATTR_MODULEis somehow causing assertion failures and unclosed resources intest_asyncio:Details
Any ideas on why that might be are definitely appreciated... I've been staring at this for a while and am completely at a loss.The rest of the PR is ready for review, though.https://bugs.python.org/issue46841