[SelectionDAG] Flags are dropped when creating a new FMUL #66701
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
While simplifying some vector operators in DAG combine, we may need to create new instructions for simplified vectors. At that time, we need to make sure that all the flags of the new instruction are copied/modified from the old instruction. Here's an example where "contract" flag is dropped when FMUL is createted. Replacing.2 t42: v2f32 = fmul contract t41, t38 With: t48: v2f32 = fmul t38, t38
jayfoad
reviewed
Sep 19, 2023
Contributor
jayfoad
left a comment
jayfoad
left a comment
There was a problem hiding this comment.
Code change looks good. Could you pre-commit the new test case (no review required) and then rebase this patch on it?
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
3 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Outdated suggestions cannot be applied.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.
While simplifying some vector operators in DAG combine, we may need to create new instructions for simplified vectors. At that time, we need to make sure that all the flags of the new instruction are copied/modified from the old instruction.
If "contract" is dropped from an instruction like FMUL, it may not generate FMA instruction which would impact performance.
Here's an example where "contract" flag is dropped when FMUL is created.
Replacing.2 t42: v2f32 = fmul contract t41, t38
With: t48: v2f32 = fmul t38, t38