: selection: bugfix reifying strided views #533
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This pull request was exported from Phabricator. Differential Revision: D78315005 |
Summary: **fix two bugs** thanks go to pzhan9 for reporting these issues! (see D78298712) (1) one in `reify_view` where views with strides were reified incorrectly. the old code assumed views could always be expressed as contiguous `range(start..start + len)` expressions, even when the view's stride differed from the base. this produced incorrect selections when the view was strided relative to the base layout. the fix is to recognize when a view is layout-aligned; that is, when each of its strides is an integer multiple of the corresponding base stride, including the unitary case; and to reify such views using `Range(start, Some(end), step)` expressions that preserve both shape and layout. previously, only the unitary case (`step` = 1) was handled. this change extends support to non-unitary aligned views, such as `step` = 2, by correctly computing the step factor and corresponding end coordinate. if any dimension is not layout-aligned — that is, if `view_stride` % `base_stride` ≠ 0 — we conservatively fall back to enumerating all selected coordinates explicitly. (2) also fixes a bug in `Shape::select()` where the length of a strided range was computed using truncating division. this now correctly uses ceiling division to ensure all selected indices are included. Differential Revision: D78315005
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Summary:
fix two bugs
thanks go to pzhan9 for reporting these issues! (see D78298712)
(1) one in
reify_viewwhere views with strides were reified incorrectly. the old code assumed views could always be expressed as contiguousrange(start..start + len)expressions, even when the view's stride differed from the base. this produced incorrect selections when the view was strided relative to the base layout.the fix is to recognize when a view is layout-aligned; that is, when each of its strides is an integer multiple of the corresponding base stride, including the unitary case; and to reify such views using
Range(start, Some(end), step)expressions that preserve both shape and layout. previously, only the unitary case (step= 1) was handled. this change extends support to non-unitary aligned views, such asstep= 2, by correctly computing the step factor and corresponding end coordinate.if any dimension is not layout-aligned — that is, if
view_stride%base_stride≠ 0 — we conservatively fall back to enumerating all selected coordinates explicitly.(2) also fixes a bug in
Shape::select()where the length of a strided range was computed using truncating division. this now correctly uses ceiling division to ensure all selected indices are included.Differential Revision: D78315005