elab: desugar &arr[i] to arr + i for array-shaped pointers#119
Merged
Conversation
C defines `&E1[E2]` to be exactly `(E1) + (E2)`. PAL's emit pass was not honouring that identity: for an `_array T*` or `_arrayptr T*` operand, the inner Index node could not produce an lvalue, so the surrounding Ref reported 'cannot produce lvalue for a[i]' (non-fatal) and substituted `(admit())`. The implicit Array->ArrayPtr coercion at the return site then wrapped that with a hardcoded `0sz` offset, silently dropping the actual index from the source. Fix in elab: when a Ref wraps an Index whose array operand has type Pointer(_, Array | ArrayPtr), rewrite the expression to a BinOp::Add and re-elaborate. BinOp::Add on those pointer kinds is already emitted correctly (array_to_arrayptr / arrayptr_shift with the real offset). True C arrays (FixedArray) are unaffected and continue to use the existing lvalue path. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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
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Outdated suggestions cannot be applied.This suggestion has been applied or marked resolved.Suggestions cannot be applied from pending reviews.Suggestions cannot be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.
C defines
&E1[E2]to be exactly(E1) + (E2). PAL's emit pass was not honouring that identity: for an_array T*or_arrayptr T*operand, the inner Index node could not produce an lvalue, so the surrounding Ref reported 'cannot produce lvalue for a[i]' (non-fatal) and substituted(admit()). The implicit Array->ArrayPtr coercion at the return site then wrapped that with a hardcoded0szoffset, silently dropping the actual index from the source.Fix in elab: when a Ref wraps an Index whose array operand has type Pointer(_, Array | ArrayPtr), rewrite the expression to a BinOp::Add and re-elaborate. BinOp::Add on those pointer kinds is already emitted correctly (array_to_arrayptr / arrayptr_shift with the real offset). True C arrays (FixedArray) are unaffected and continue to use the existing lvalue path.