Add MIGraphX execution provider support

[aditya-dl]

Add MIGraphX (AMD GPU) execution provider support to ONNX Runtime GenAI. The provider is exposed as "migraphx" to users (with "MIGraphXExecutionProvider" accepted as a catalog-name alias for compatibility with Windows ML EP discovery flows).

This PR supersedes #2093 (which used the now-reverted "AMDGPU" naming).

Changes:

• Create src/migraphx/session_options.{h,cpp} with AppendExecutionProvider that tries V2 plugin path ("MIGraphXExecutionProvider") then falls back to V1 legacy API ("MIGraphX")
• Add provider name normalization: both "migraphx" and "MIGraphXExecutionProvider" map to "MIGraphX"; register "MIGraphX" in the dispatch table
• Enable graph capture for MIGraphX to allow compiled graph reuse during token generation
• Add static input shape padding (prompt_gen_ flag) so MIGraphX avoids recompilation on varying prompt lengths. Gated behind NeedsStaticInputShapes() so it only activates for MIGraphX, not other EPs
• Fix input_ids padding to handle both int32 and int64 element types, and correct per-row copy for batch_size > 1
• Fix position_ids padding to prevent out-of-bounds read on next_tokens when tensor shape is padded to max_length for batch_size > 1

Configuration:

"provider_options": [{ "migraphx": {} }]

or

config.append_provider("migraphx")

Also accepted: "MIGraphXExecutionProvider" (catalog form, what Windows ML returns from the EP discovery API).

Known limitations:

• Beam search not supported (requires past_present_share_buffer=true which requires num_beams=1)
• Inputs allocated on CPU; the MIGraphX EP handles CPU↔GPU transfers internally

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[aditya-dl]

@kunal-vaishnavi @baijumeswani could you help review this PR?

[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

Adds MIGraphX (AMD GPU) execution provider integration to ONNX Runtime GenAI, including provider name normalization and runtime behaviors needed to avoid recompilation during prompt processing.

Changes:

• Register MIGraphX in the session-options dispatch table and add a MIGraphX EP implementation (V2 plugin path with V1 fallback).
• Normalize provider names so "migraphx" and "MIGraphXExecutionProvider" map to "MIGraphX", and enable graph capture for MIGraphX.
• Add “static input shape” prompt-time padding and update position/logits shapes to support padded prompt lengths.

Reviewed changes

Copilot reviewed 13 out of 13 changed files in this pull request and generated 11 comments.

Show a summary per file

File	Description
src/models/session_options.cpp	Adds MIGraphX EP registration in the provider dispatch map.
src/models/position_inputs.h	Updates CreateAndInitializePositionIDs signature to accept actual seq_length.
src/models/position_inputs.cpp	Implements position id initialization w/ padded shapes and safe indexing using seq_length.
src/models/model.h	Adds State::prompt_gen_ flag to control prompt-time padding behavior.
src/models/model.cpp	Pads input_ids to max_length during prompt generation for static-shape EPs.
src/models/logits.cpp	Forces logits output shape to max_length during prompt generation.
src/migraphx/session_options.h	Declares MIGraphX EP append entrypoint.
src/migraphx/session_options.cpp	Implements MIGraphX EP append with V2 plugin-first and V1 fallback.
src/generators.h	Adds use_static_input_shapes to generator params.
src/generators.cpp	Toggles prompt_gen_ around prompt vs token-generation runs.
src/config.h	Declares NeedsStaticInputShapes.
src/config.cpp	Adds MIGraphX name normalization, enables graph capture for MIGraphX, and implements NeedsStaticInputShapes.
cmake/global_variables.cmake	Adds MIGraphX sources to the CMake glob.