Fix itertype promotion for GatherScatter

[Priya2698]

This PR

Stops propagation of IterType::GatherScatter to be propagated from producer to consumer.

Context

We are propagating IterType::GatherScatter, in the example below, the output T2 from scatter op contains nS2 in logical domain. That IterType is propagated through to its consumer T3, which felt wrong.

%kernel {
T2_l_int64_t[iS3{1024}]
   = scatter(in = T0_g_int64_t[iS0{128}], dim = 0, src = 1, idx = T1_g_int64_t[iS1{1024}], accumulate = add )
T3_g_int64_t[nS4{128}]
   = T2_l_int64_t[iS3{1024}]
   + 1;

T2_l_int64_t[iS3{1024}]
 logical domain : (nS2{128})
 contiguity: t
 loop domain : (iS3{1024})
T3_g_int64_t[nS4{128}]
 logical domain : (nS4{128})
 contiguity: t
 loop domain : (nS4{128})
} // %kernel

[Priya2698]

!test

[github-actions]

Review updated until commit 12d6f71

Description

• Fix iter_type promotion for GatherScatter axes

• Add test for GatherScatter iter type behavior

• Ensure non-Scatter Tvs don't have GatherScatter axes

---

Changes walkthrough 📝

	Relevant files
Bug fix	utils.cpp Fix iter_type promotion for GatherScatter                                csrc/ops/utils.cpp Fix iter_type handling for GatherScatter IDs Set iter_type to Iteration when ID is GatherScatter Preserve existing promotion logic otherwise +2/-0
Tests	test_scatter.cpp Add test for GatherScatter iter type                                          tests/cpp/test_scatter.cpp Add test case for GatherScatter iter type Validate loop domains exclude GatherScatter axes Test non-Scatter tensors in fusion +25/-0

---

PR Reviewer Guide 🔍

Here are some key observations to aid the review process:

🧪 PR contains tests

⚡ Recommended focus areas for review Possible Logic Error The promotion of iter_type for GatherScatter axes may not correctly handle all cases, as setting IterType::Iteration unconditionally on isGatherScatter could override meaningful iter types from other paths. This may affect downstream optimizations relying on accurate iter_type. } else if (id->isGatherScatter()) { iter_type = IterType::Iteration; } else {

[Priya2698]

This is same as ScatterLargeConstrainedIDs.
I have made this separate to keep it independent of the other test in case it is modified in the future according to its purpose.

[Priya2698]

!test

[jjsjann123]

LGTM.