Add WhereDummyDq Transformer to form Node Unit

[qti-hungjuiw]

Description

• Add a GraphTransformer WhereDummyDq to insert dummy DequantizeLinear on Where node's initializer input to form a Node Unit when Where node has one DQ and one scalar initializer input
• Add corresponding unit test for the optimization

Motivation and Context

• To reduce the additional Dequantize and Quantize nodes, we would like to pass WhereNodeGroupSelector::Check.

[qti-hungjuiw]

@microsoft-github-policy-service agree company="Qualcomm"

[qti-hungjuiw]

Hi, the PR aims to improve the performance of QDQ models by removing additional QDQ nodes around where operator.

• The current use case targets the QNN EP. Please let me know if any modification is required, such as adding compatible_execution_providers.

[Copilot]

Pull Request Overview

This PR adds a new WhereDummyDq graph transformer to insert dummy DequantizeLinear nodes on Where node's initializer inputs to form Node Units when the Where node has one DQ input and one scalar initializer input. This optimization helps reduce additional Dequantize and Quantize nodes by enabling the WhereNodeGroupSelector::Check to pass.

Key changes:

• Added new WhereDummyDq transformer class that identifies Where nodes with mixed DQ and scalar inputs
• Implemented logic to insert dummy DQ nodes with appropriate scale/zero-point values derived from existing DQ nodes
• Integrated the transformer into the optimization pipeline at Level1

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 4 comments.

File	Description
where_dummy_dq.h	Header file defining the WhereDummyDq transformer class interface
where_dummy_dq.cc	Implementation of the transformer logic including condition checking and dummy DQ insertion
graph_transformer_utils.cc	Integration of WhereDummyDq transformer into the Level1 optimization pipeline
qdq_transformer_test.cc	Unit tests covering various scenarios for the WhereDummyDq transformer

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