[Qiming Bao (14H034160212)]

Description

PropagateCastOps throws when a Cast it removes feeds the same consumer more than once, as in Where(condition, C, C).

RemoveCastNodesChain and the multi-child branch of RemoveBackToBackCasts looked up the consumer input with optimizer_utils::IndexOfNodeInput, which returns the first match. They removed and re-added only that edge, while std::replace rewired every matching input def. The edge into the second input was left pointing at the removed Cast. Cleaning it up later then fails:

• One child Cast, which is the reproduction in the issue: Graph::RemoveEdge ... Argument mismatch when removing edge.
• The FLOAT Cast has another consumer: Graph::RemoveNode ... Can't remove node ... as it still has output edges.

Both loops now go over every input of the consumer that reads the removed output, and move each edge.

Motivation and Context

Fixes #34192.

Tests

New test GraphTransformationTests.PropagateCastOpsTests_RepeatedConsumerInput builds X(fp16) -> Cast(float) -> Cast(fp16) -> C, Y = Where(true, C, C). A second variant gives the float Cast another consumer, which exercises the multi-child branch. Each variant runs with both strategies at levels 0 to 2 through TestGraphTransformer. The test checks that the fp16 Cast is removed and that both Where data inputs read the graph input.

• On main, the test fails with the two exceptions above.
• With this change, it passes.
• onnxruntime_test_all --gtest_filter='GraphTransformation*:*Optimizer*:*Fusion*:GraphUtils*:*PropagateCast*': 793 tests pass (Linux, CPU, Release).

[azure-pipelines]

Azure Pipelines:
There may be pipelines that require an authorized user to comment /azp run to run.

[Copilot]

🟢 Approval recommended

There are no active review issues for the fix preserving graph connectivity when Cast removal affects multiple inputs of the same consumer.

No open issues 🎉

What changed in this PR

Fixes #34192 by making PropagateCastOps preserve graph connectivity when a removed Cast feeds multiple inputs of the same consumer, such as Where(condition, C, C).

Changes:

• Rewires every matching consumer input edge in cast-chain removal and the multi-child back-to-back Cast removal path.
• Adds regression coverage for both removal paths, both propagation strategies, and levels 0–2.

File	Description
onnxruntime/​test/​optimizer/​graph_transform_test.cc	Adds repeated-consumer-input tests with and without another consumer of the FLOAT Cast.
onnxruntime/​core/​optimizer/​propagate_cast_ops.cc	Updates both removal loops to move each affected edge and input definition together.

_{Review effort: Balanced}