Add signed BitShift support for opset 28

[Justin Chu (justinchuby)]

Description

Adds ONNX BitShift opset 28 support for signed int8, int16, int32, and int64 tensors while preserving unsigned support.

• Implements arithmetic right shift and raw-bit left shift without signed C++ shift undefined behavior.
• Handles negative and out-of-range shift counts with the opset-28 0/-1 saturation semantics.
• Splits CPU registrations at opset 28 and enables the previously missing uint16 kernel.
• Caps DirectML's native BitShift kernel at opset 27 because DirectML masks out-of-range counts; opset 28 falls back to CPU for correct behavior.
• Adds focused signed, unsigned, scalar, broadcast, wraparound, and out-of-range tests, and enables the ONNX uint16 backend tests.

Stacked on #32359.

Validation

onnxruntime_provider_test build is currently blocked by the base branch's unrelated tensorprotoutils.h numeric datatype map static assertion after the ONNX c78026fa update. The failure occurs across unrelated provider translation units before BitShift tests can link.

[Copilot]

🟡 Changes recommended

Generated kernel documentation is stale, backend exclusions remain, and the DirectML fallback boundary lacks targeted coverage.

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Pull request overview

Adds CPU support for signed BitShift in opset 28 while preserving earlier unsigned behavior.

Changes:

• Implements defined signed shift and saturation semantics.
• Splits CPU registrations and enables uint16.
• Caps DirectML support at opset 27 and expands tests.

File summaries

File	Description
onnxruntime/core/providers/cpu/math/element_wise_ops.cc	Implements safe shifts and registrations.
onnxruntime/core/providers/cpu/cpu_execution_provider.cc	Registers opset-specific CPU kernels.
onnxruntime/core/providers/dml/DmlExecutionProvider/src/AbiCustomRegistry.cpp	Caps DirectML BitShift support.
onnxruntime/test/providers/cpu/math/element_wise_ops_test.cc	Adds signed and unsigned tests.
onnxruntime/test/onnx/TestCase.cc	Enables uint16 C++ backend tests.

Review details

Suppressed comments (1)

onnxruntime/core/providers/cpu/math/element_wise_ops.cc:1394

• This else is unnecessary after the signed branch returns and violates the repository's AGENTS.md:108 no-else-after-return convention.

  } else {
    return result;

• Files reviewed: 5/5 changed files
• Comments generated: 5
• Review effort level: Balanced

---

💡 Configure MCP servers for context-aware, tailored reviews. Learn more in the docs.