cont_engine: evaluate a zero-volume general product through a tile-less evaluator - #590
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…ss evaluator init_distribution_general skips the process grid for a zero-volume result (ProcGrid needs at least one row and one column), but make_dist_eval_general still built the SUMMA evaluator and its canonical slabbed pmap from proc_grid_, tripping TA_ASSERT(world_) in ProcGrid::make_pmap. The result has no tiles, so evaluate it through ZeroVolumeEvalImpl, a DistEvalImpl that owns no tiles and produces nothing. Hit by a shape-imposed ToT product whose sliced aux mode had no tiles.
It is a DistEvalImpl that owns no tiles, not a contraction detail, so it belongs next to the other distributed evaluators rather than in expressions/cont_engine.h -- which also relied on picking up DistEvalImpl transitively through dist_eval/contraction_eval.h. Installed alongside the other dist_eval headers.
A result mode with no tiles makes the general product's result zero-volume, which is the corner case where init_distribution_general skips the process grid. Covers all three ways the result volume vanishes -- an empty left external (M == 0), fused (n_slabs_ == 0), and right external (N == 0) mode -- with canonical and repermuted targets, dense and block-sparse. Four of those six combinations abort without the ZeroVolumeEvalImpl path (TA_ASSERT(world_) in ProcGrid::make_pmap, or nh_ > 0 in contraction_eval). Also pins the adjacent case that must keep taking the ordinary path: an empty *contracted* mode, whose result still has tiles and is zero.
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@kshitij-05 still a draft? |
kshitij-05
marked this pull request as ready for review
September 18, 2026 20:37
evaleev
approved these changes
Sep 18, 2026
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Problem
ContEngine::init_distribution_generalskips the process grid when the general (fused x contracted) product's result has zero volume -- some result mode has no tiles, andProcGridneeds at least one row and one column -- butmake_dist_eval_generalstill built the batched SUMMA evaluator and its slab-replicated pmap from the default-constructedproc_grid_, trippingTA_ASSERT(world_)inProcGrid::make_pmap(orTA_ASSERT(nh_ > 0)incontraction_eval.h). Hit by a shape-imposed tensor-of-tensor product whose sliced aux mode had no tiles.Fix
dist_eval/zero_volume_eval.h:ZeroVolumeEvalImpl, aDistEvalImplover a zero-volume tiled range: it owns no tiles,internal_eval()spawns nothing, andget_tilethrows. Installed alongside the otherdist_evalheaders.expressions/cont_engine.h: whentrange_.tiles_range().volume() == 0,make_dist_eval_generalreturns that evaluator in the target layout, with the pmapinit_distribution_generalchose, instead of building the SUMMA evaluator (whose operands are then not evaluated either).Testing
general_product_suite(tests/general_product.cpp):expression_general_product_zero_volume_denseand..._sparse: all three ways the result volume vanishes -- an empty left-external (M == 0), fused (n_slabs_ == 0) and right-external (N == 0) mode -- each with a canonical and a repermuted target, onDensePolicyandSparsePolicy. Without the fix four of the six combinations abort inProcGrid::make_pmap/contraction_eval.h.expression_general_product_zero_volume_contracted_mode: control -- an empty contracted mode keeps the ordinary process-grid path and yields a zero array with tiles.Local run (macOS arm64,
TA_ASSERT_THROW):ta_test --run_test=general_product_suite-> no errors; the same test file built against master fails the two zero-volume cases. GitHub Actions and GitLab CI green.