[LowerFirReg] Reimplement the mux reachability analysis #6914
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
WIP wip wip Fix lit test Fixup
|
What was the issue and fix here? |
Windows builder specifically errored because the SmallVector's element size crossed a threshold. CI build failure (Windows doesn't run on PR's but was promptly reverted until fixed (thanks!)): Looks like fix was doing what was asked by that error and explicitly specifying number of elements to allocate, here: |
|
Thanks @dtzSiFive , that's right. The issue was default vector size, which was fixed in the commit. |
|
Thanks, just wanted to make sure what was going on :) Thank you for the details. |
cepheus69
pushed a commit
to cepheus69/circt
that referenced
this pull request
Apr 22, 2024
This implements a new heuristic to determine if a Mux is reachable from a FirReg. In general an operation is reachable from a register if its in the fanout of the register. For FirReg lowering, an if/else structure is required for proper enable inference, if a mux is within the fanout from the register. The fanout path can only consist of MuxOp, ArrayGetOp or ArrayCreateOp. Thus any ops other than MuxOp, ArrayGetOp or ArrayCreateOp block the reachability. The analysis is built lazily when its queried and the result is cached to avoid redundant traversal of the IR. This fixes an issue that caused the merged commit for llvm#6709 to be reverted. The was to explicitly specify the default size of `SmallVector`.
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Outdated suggestions cannot be applied.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.
Reopened the PR #6709 , after fixing the issue that required the merged
commit to be reverted.
This implements a new heuristic to determine if a Mux is reachable from a
FirReg. In general an operation is reachable from a register if its in the
fanout of the register. For FirReg lowering, an if/else structure is required
for proper enable inference, if a mux is within the fanout from the register.
The fanout path can only consist of MuxOp, ArrayGetOp or ArrayCreateOp.
Thus any ops other than MuxOp, ArrayGetOp or ArrayCreateOp block the
reachability. The analysis is built lazily when its queried and the result is
cached to avoid redundant traversal of the IR.