[pmo] Assigns should result in PMO not eliminating an allocation. #22018
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
The reason this is true is that an assign is an instruction in PMO parlance that must destroy the value stored into memory at that location previously. So PMO would need to be taught to ensure that said destroy is promoted. Consider the following example: %0 = alloc_stack $Foo store %1 to [init] %0 : $*Foo store %2 to [assign] %0 : $*Foo destroy_addr %0 : $*Foo dealloc_stack %0 : $*Foo If PMO were to try to eliminate the alloc_stack as PMO is written today, one would have: destroy_value %2 : $Foo That is clearly wrong.
|
@swift-ci smoke test and merge |
1 similar comment
|
@swift-ci smoke test and merge |
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Outdated suggestions cannot be applied.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.
The reason this is true is that an assign is an instruction in PMO parlance that
must destroy the value stored into memory at that location previously. So PMO
would need to be taught to ensure that said destroy is promoted. Consider the
following example:
%0 = alloc_stack $Foo
store %1 to [init] %0 : $*Foo
store %2 to [assign] %0 : $*Foo
destroy_addr %0 : $*Foo
dealloc_stack %0 : $*Foo
If PMO were to try to eliminate the alloc_stack as PMO is written today, one
would have:
destroy_value %2 : $Foo
That is clearly wrong.