release/18.x: Fix overflow flag for i128 USUBO #86475
Closed
Conversation
This file contains 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
We use the VSCBIQ/VSBIQ/VSBCBIQ family of instructions to implement USUBO/USUBO_CARRY for the i128 data type. However, these instructions use an inverted sense of the borrow indication flag (a value of 1 indicates *no* borrow, while a value of 0 indicated borrow). This does not match the semantics of the boolean "overflow" flag of the USUBO/USUBO_CARRY ISD nodes. Fix this by generating code to explicitly invert the flag. These cancel out of the result of USUBO feeds into an USUBO_CARRY. To avoid unnecessary zero-extend operations, also improve the DAGCombine handling of ZERO_EXTEND to optimize (zext (xor (trunc))) sequences where appropriate. Fixes: llvm#83268 (cherry picked from commit d9c31ee)
uweigand
requested changes
Mar 25, 2024
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Outdated suggestions cannot be applied.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.
Backport d9c31ee
Requested by: @uweigand