[SIL] Added borrow scopes to alloc_boxes. #40793
Merged
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
nate-chandler
force-pushed
the
silgen/emit-borrow-scopes-for-alloc_boxes
branch
3 times, most recently
from
d411337 to
3293c8e
Compare
Because AllocBoxToStack is not able to transform every alloc_box into an alloc_stack, it's necessary to add begin_borrow [lexical] to every alloc_box in order to provide lexical scopes for those alloc_boxes which will not be transformed into alloc_stacks.
Now that alloc_boxes whose lifetimes are lexical are emitted with begin_borrow [lexical]/end_borrow, AllocBoxToStack needs to be able to see through those new borrow scopes in order to continue stack promoting the same boxes that it was able to before those lexical scopes were emitted.
nate-chandler
force-pushed
the
silgen/emit-borrow-scopes-for-alloc_boxes
branch
from
3293c8e to
f19e413
Compare
|
@swift-ci please benchmark |
|
@swift-ci please test |
Performance (x86_64): -O
Code size: -OPerformance (x86_64): -Osize
Code size: -OsizePerformance (x86_64): -Onone
Code size: -swiftlibsHow to read the dataThe tables contain differences in performance which are larger than 8% and differences in code size which are larger than 1%.If you see any unexpected regressions, you should consider fixing the Noise: Sometimes the performance results (not code size!) contain false Hardware Overview |
atrick
approved these changes
Jan 13, 2022
|
Build failed |
|
@swift-ci please test macos platform |
nate-chandler
added a commit
to nate-chandler/swift
that referenced
this pull request
Mar 11, 2022
After swiftlang#40793, alloc_boxes all have their lifetimes protected by a lexical borrow scope. In that PR, DI had been updated to see through begin_borrow instructions from a project_box to a mark_uninitialized. It did not, however, correct the end_borrow instructions when destroy_values of mark_uninitializeds were replaced with destroy_addrs of project_boxes. That is done here. In a bit more detail, in the following context %box = alloc_box %mark_uninit = mark_uninitialized %box %lifetime = begin_borrow [lexical] %mark_uninit %proj_box = project_box %lifetime When it is not statically known whether a field is initialized, we are replacing the instruction // before destroy_value %mark_uninit // after with the following diamond // before %initialized = load cond_br %initialized, yes, no yes: destroy_addr %proj_box br bottom no: br bottom bottom: dealloc_box %box br keep_going keep_going: // after Doing so is problematic, though, because by SILGen construction the destroy_value is always preceded by an end_borrow: end_borrow %lifetime destroy_value %mark_uninit Previously, that end_borrow remained above the %initialized = load instruction in the above. That was invalid because the the newly introduced destroy_addr %proj_box was a use of the borrow scope (%proj_box is a projection of the begin_borrow) and consequently must be within the borrow scope. Note also that it would not be sufficient to simply emit the diamond before the end_borrow. The end_borrow must come before the destruction of the value whose lifetime it is protecting (%box), and the diamond contains the instruction to destroy that value (dealloc_box) in its bottom block. To resolve this issue, just move the end_borrow instruction from where it was to before the dealloc box. (This is actually done by moving it to the top of the diamond's "continue" block prior to the emission of that dealloc_box instruction.) rdar://89984216
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
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.
Because AllocBoxToStack is not able to transform every alloc_box into an alloc_stack, it's necessary to add begin_borrow [lexical] to every alloc_box in order to provide lexical scopes for those alloc_boxes which will not be transformed into alloc_stacks.
Now that alloc_boxes whose lifetimes are lexical are emitted with begin_borrow [lexical]/end_borrow, AllocBoxToStack needs to be able to see through those new borrow scopes in order to continue stack promoting the same boxes that it was able to before those lexical scopes were emitted.