fix[next]: symbolic domain union for empty domains (static case) by tehrengruber · Pull Request #2677 · GridTools/gt4py

tehrengruber · 2026-06-29T10:00:59Z

Domain inference computes the union of two domains as the per-dimension convex hull:

union(A, B) = [ min(A.start, B.start), max(A.stop, B.stop) [

This is wrong when the inputs are empty (start >= stop). The union of two empty domains should stay empty, but min/max produces a non-empty range:

A = [10, 10[ (empty)
B = [11, 11[ (empty)

union(A, B) = [ min(10, 11), max(10, 11) [ = [10, 11[

so two empty domains wrongly union to the non-empty [10, 11[.

This shows up in practice with concat_where: a branch that is never selected produces an empty domain, and previously the empty range leaked into the min/max and over-approximated the inferred domain (#2205).

Fix

An empty domain is the identity element of union, so empty ranges are dropped before folding rather than fed into min/max (_reduce_ranges in domain_utils.py). The union of only empty domains then correctly stays empty.

Scope

This PR only handles static domains — concrete integer bounds, where emptiness is decidable. The symbolic case (runtime-sized bounds like [0, n[, where emptiness can't be decided at compile time and empty ranges must instead be guarded with conditional expressions) is considerably more involved and is left to a follow-up. A prototype implementation can be found in #2673.

tehrengruber · 2026-07-01T12:31:24Z

@@ -69,53 +61,86 @@ def test_domain_op_preconditions():


 def test_domain_union():


These tests have a static domain now. In #2673 both cases are covered again.

tehrengruber · 2026-07-01T12:32:03Z


    actual = global_tmps.create_global_tmps(testee, offset_provider, uids=uids)
    actual = ct.CollapseTuple.apply(actual, uids=uids)
+    actual = cf.ConstantFolding.apply(


This is a detail originating from the fact that empty domains are now returned as is, without constant folding.

havogt · 2026-07-02T06:39:14Z

+
+    This function only computes the correct value if the (non-empty) ranges are either
+    overlapping / adjacent or empty, as calculation is by means of the convex hull. Non-static
+    ranges may not be empty for now.


What does "may not be empty" mean? Does it mean they are not detected as empty or that something breaks if they are not empty?

It breaks (in the sense that the bug that this PR addresses for static ranges occurs).

havogt

lgtm

## Problem `_reduce_ranges` in `domain_utils.py` is shared by `domain_union` and `domain_intersection`: ```python _range_union = functools.partial(_reduce_ranges, start_reduce_op=im.minimum, stop_reduce_op=im.maximum) _range_intersection = functools.partial(_reduce_ranges, start_reduce_op=im.maximum, stop_reduce_op=im.minimum) ``` #2677 taught it to drop statically empty ranges before folding. That is correct for the **union**, where an empty range is the identity element, but wrong for the **intersection**, where an empty range is the *absorbing* element. Dropping the empty range from an intersection returns the remaining range instead of staying empty: ``` [1, 1[ & [0, 10[ -> [0, 10[ # should be empty [1, 1[ & [0, inf[ -> [0, inf[ # should be empty ``` The second form is reached in practice: `promote_domain` fills non-condition dimensions with `[-inf, inf[`, and `_infer_concat_where` intersects that with the target domain. If the target range is statically empty, the half-infinite range survives verbatim and an `InfinityLiteral` leaks into the inferred domain. ## Symptoms Both show up in ICON4Py with `concat_where` over a statically-known-empty vertical range (a Rayleigh damping layer of zero thickness, where the layer bound is bound as a compile-time static arg): - **gtfn** — the leaked `InfinityLiteral` reaches `itir_to_gtfn_ir._make_domain`: ``` TypeError: 'BinaryExpr.lhs' must be <class '...gtfn_ir_common.Expr'> (got 'InfinityLiteral.POSITIVE' which is a <class '...iterator.ir.InfinityLiteral'>). ``` - **dace** — `gtir_to_sdfg_concat_where` calls `domain_intersection(source_domain, output_domain)` directly at lowering time, with finite bounds. No infinity, no crash: a scalar `concat_where` branch whose range is empty (`[1, 1[`) is widened to the full output domain (`[1, 10[`), so the constant branch is broadcast over the whole domain and silently overwrites the real values. The dace case is a silent wrong-results bug, so it is worth backporting alongside the crash. ## Fix Split the two operations. The union keeps dropping empty ranges; the intersection returns the empty range directly. Emptiness remains decidable only for static ranges — non-static ranges may not be empty, as before. Also restores the constant folding that #2677 skipped in the single-surviving-range case. ## Testing - Two regression tests in `test_domain_utils.py` covering the finite and the half-infinite case. Both fail on `main`. - `tests/next_tests/unit_tests/` A/B'd with and without the change: no new failures. - Verified against ICON4Py (C2SM/icon4py#1350): the gtfn `TypeError` and the dace `diff_multfac_n2w` mismatch both disappear, and the previously-failing GAUSS3D driver integration test passes. Follow-up on #2677, related to #2205. The symbolic (non-static) case is still left to #2673. 🤖 Generated with [Claude Code](https://claude.com/claude-code) --------- Co-authored-by: Hannes Vogt <claude@mail.havogt.de> Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com> Co-authored-by: Till Ehrengruber <till.ehrengruber@cscs.ch>

tehrengruber added 2 commits July 1, 2026 08:00

Minimal version for static domains

85ab0c4

Fix failing tests

2a19d8a

tehrengruber force-pushed the fix_concat_where_static_domains branch from cc072a8 to 2a19d8a Compare July 1, 2026 09:01

tehrengruber added 2 commits July 1, 2026 11:49

Fix format

7580438

Fix format

a2133f6

tehrengruber commented Jul 1, 2026

View reviewed changes

tehrengruber requested a review from havogt July 1, 2026 12:32

Merge branch 'main' into fix_concat_where_static_domains

7dff4f3

havogt reviewed Jul 2, 2026

View reviewed changes

havogt approved these changes Jul 2, 2026

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tehrengruber merged commit d651e4d into main Jul 2, 2026
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havogt mentioned this pull request Jul 10, 2026

fix[next]: empty range is absorbing for domain intersection #2702

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fix[next]: symbolic domain union for empty domains (static case)#2677

fix[next]: symbolic domain union for empty domains (static case)#2677
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		@@ -69,53 +61,86 @@ def test_domain_op_preconditions():


		def test_domain_union():

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tehrengruber commented Jun 29, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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tehrengruber commented Jun 29, 2026 •

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