RVV 0.9: Tighten fractional LMUL-SEW constraint #2484
Merged
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
The spec requires that implementations support fractional LMUL settings for LMUL ≥ SEW/ELEN. The old code enforced the looser constraint that LMUL ≥ SEW/VLEN, so e.g. if VLEN were twice ELEN, we would support one notch smaller LMUL for any given SEW. Tightening the constraint will catch software bugs that rely on vtype settings that aren't guaranteed to be supported across implemenetations. The space of configurations that need to be verified is also reduced.
aswaterman
force-pushed
the
tighten-fractional-lmul-constraint
branch
from
be150a3 to
d1cce9f
Compare
solomatnikov
approved these changes
May 22, 2020
There was a problem hiding this comment.
LGTM
My reading of spec is that this is a requirement: riscvarchive/riscv-v-spec#479 (comment)
riscvarchive/riscv-v-spec#479 (comment)
Other people also thought the same way: riscvarchive/riscv-v-spec#479 (comment)
|
Ah, thanks for the pointer. I support tightening the spec (or clarifying, depending on your POV). |
aswaterman
added a commit
that referenced
this pull request
Jun 8, 2020
This reverts commit 6249be3.
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Outdated suggestions cannot be applied.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 spec requires that implementations support fractional LMUL settings
for LMUL ≥ SEW/ELEN. The old code enforced the looser constraint that
LMUL ≥ SEW/VLEN, so e.g. if VLEN were twice ELEN, we would support one
notch smaller LMUL for any given SEW.
Tightening the constraint will catch software bugs that rely on vtype
settings that aren't guaranteed to be supported across implemenetations.
The space of configurations that need to be verified is also reduced.
Type of change: other enhancement
Impact: API modification
Development Phase: implementation