Fix incorrect num_items in reduction for small kernels. #2477
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Ensures num_items is recalculated after updating group_width when num_items is less than max_sg_sz, preventing incorrect parallelism configuration.
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Pull request overview
This PR fixes a bug in the reduction kernel configuration logic where num_items was not being updated after adjusting group_width for small kernels. The fix ensures correct memory access patterns and resolves product reduction failures in unit tests.
Key Changes:
- Recalculate
num_itemsafter updatinggroup_widthwhen the initialnum_itemsis less thanmax_sg_sz
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Ensures num_items is recalculated after updating group_width when num_items is less than max_sg_sz, preventing access to wrong memory later and fixes prod reduction for small kernels. Fixes some UTs from #1818.