Some improvements to the compiler's handling of function alignment #21710
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
alexrp
commented
Oct 15, 2024
alexrp
commented
Oct 15, 2024
mlugg
reviewed
Oct 19, 2024
…r more targets. defaultFunctionAlignment() can be made more sophisticated over time based on the CPU model and/or features. For now, I've picked some reasonable values for the CPUs that are most commonly used in practice. (Values are sourced from LLVM.)
minFunctionAlignment() is something we can know ahead of time for any given target because it's a matter of ABI. However, defaultFunctionAlignment() is a matter of optimization and every backend can do it differently depending on any number of factors. For example, LLVM will base the choice on the CPU model in its aarch64 backend. So just don't use this value in the frontend.
…cified. max(user_align, minFunctionAlignment()) is only appropriate when the user has actually given an explicit, non-zero alignment value.
…he linker. In particular, for user-specified alignment values, we need to do max(user_align, minFunctionAlignment()) to respect the ABI minimum.
alexrp
force-pushed
the
function-alignment
branch
from
b4cfd4b to
6c1e306
Compare
mlugg
approved these changes
Oct 23, 2024
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
2 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Outdated suggestions cannot be applied.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.
No description provided.