Precompute: Avoid caching heap values of partial precomputations #7766
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
Closed
src/passes/Precompute.cpp
Outdated
Comment on lines
732
to
733
| usedHeapValues ? *usedHeapValues | ||
| : heapValues, |
Member
There was a problem hiding this comment.
Maybe we simplify things by moving this logic to the very top of the function:
if (!usedHeapValues) {
usedHeapValues = &heapValues;
}
tlively
approved these changes
Jul 29, 2025
kripken
added a commit
that referenced
this pull request
Aug 8, 2025
Precompute has two modes, one where we ignore effects. We were caching the effectless results for where the normal mode (which cares about effects) would reuse them, leading to bugs. Fixes a regression from #7763, another after #7766. We were not using the cache fully, before, and caches are bug-prone, sadly.
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Outdated suggestions cannot be applied.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.
Fixes a regression from #7763
This is pretty subtle, unfortunately. We cache the results of a
struct.newetc as we go, so that identity is preserved for precomputing RefEq etc.
The old code always computed structs in full before checking the cache.
#7763 removed that code as an optimization. But, it turns out,
that was load-bearing in that it, by pure luck, happened to avoid a bug.
The bug that was avoided, and which this PR fixes, is that when we
partially precompute, we modify a
struct.newand see if we canprecompute that version. We were still using the same heap value
cache, so we could cache the value, then later end up using it for
the original (before, we'd still compute the
struct.newagain anduse those values). To fix that, do such speculative precomputations on a
side (throwaway) cache.
Fixes #7765