Copy outer-scope initializers used only from a subgraph when compiling

[hcl (hclsys)]

Fixes #32131.

CompileModel / OrtCompileApi fails on any model where a subgraph (If/Loop/Scan body) reads an initializer of an enclosing graph that no node of the enclosing graph reads itself — which the ONNX IR spec allows, and which InferenceSession and optimized_model_filepath handle fine.

CreateEpContextModel (graph_partitioner.cc) copies an initializer into the EPContext graph only when a NodeArg of that name already exists. ep_graph.AddNode() creates NodeArgs for a node's own inputs/outputs but not for names its subgraphs consume from outer scope (implicit inputs), so a subgraph-only initializer is skipped and the following ep_graph.Resolve() fails on the dangling reference.

Fix: also copy initializers named by a node's ImplicitInputDefs(). MakeInitializerCopyIfNotExist creates the NodeArg for the copied initializer, so the outer-scope reference resolves.

Verified locally (built with the change): a minimal If model whose branches read outer-scope axes/data no outer node reads now compiles (ModelCompiler.compile_to_bytes succeeds) where it previously raised INVALID_GRAPH. Added a regression test test_compile_model_with_outer_scope_initializer_used_only_in_subgraph to onnxruntime_test_python_compile_api.py.

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[Copilot]

Pull request overview

Note

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

Fixes EPContext model creation so outer-scope initializers referenced only by subgraphs (implicit inputs) are still copied, preventing resolve/compile failures; adds a regression test for this scenario.

Changes:

• Add a Python regression test that builds an If model whose branch bodies reference outer-scope initializers.
• Update EPContext model construction to also copy initializers that are referenced as implicit inputs in subgraphs.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
onnxruntime/test/python/onnxruntime_test_python_compile_api.py	Adds a compile regression test where subgraphs consume only outer-scope initializers.
onnxruntime/core/framework/graph_partitioner.cc	Ensures initializers referenced via implicit inputs are copied into the EPContext model to avoid dangling references.

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[hcl (hclsys)]

On the copilot note about scanning graph.Nodes(): the AddNode loop just above adds every node of graph.Nodes() to ep_graph (either its EPContext replacement or the node itself), so the scan does not pull in nodes absent from ep_graph. The only over-copy case is a subgraph node that gets fused into an EPContext node — its outer-scope initializer would be copied but unused, which is harmless and bounded to initializers a subgraph actually references. Can scope the scan to the surviving nodes if you would rather avoid that.