Fix dead dedup guard in GraphTransformerManager::Register (audit F10)

[GopalakrishnanN]

Description

GraphTransformerManager::Register guarded against duplicate registration with a std::find over level_to_transformer_map_[level] (a container of std::unique_ptr<GraphTransformer>) looking for the transformer unique_ptr about to be inserted. Since that unique_ptr is not yet in the container and owns a distinct pointer, the comparison can never match — the guard is dead code.

As a result, a transformer registered with a duplicate name at the same level slips through: it is appended a second time to level_to_transformer_map_[level] and applied twice per optimization pass, and the intended "already registered" error is never returned.

Fix

Replace the dead identity check with a per-level name check backed by an O(1) hash lookup: each transformer's name is recorded in the existing transformers_info_ map keyed by (level, name), so a duplicate at the same level is rejected in constant time instead of scanning the transformers already registered at that level (avoiding the quadratic registration cost). This preserves the original per-level intent — the same transformer name at different levels remains valid (e.g. LayerNormFusion is registered at both Level1 and Level2 by GenerateTransformers), which a global-name check would have wrongly rejected.

Tests

Adds GraphTransformationTests.RegisterDuplicateTransformerNameFailsPerLevel:

• same name, same level → FAIL
• same name, different level → OK

Verified locally: the test fails on the pre-fix code (duplicate_status.IsOK() was true, i.e. the duplicate was wrongly accepted) and passes with the fix. The full GraphTransformationTests suite remains green after the O(1) revision — re-verified on a RelWithDebInfo build (350 passed, 15 CUDA/WebGpu skipped, 0 failed), including the layernorm tests that register the same fusion at Level1 and Level2.

Motivation and Context

Fixes the design-audit F10 finding — a non-functional safeguard that silently allowed duplicate transformer registration and double-application.

[Copilot]

Pull request overview

Fixes a non-functional duplicate-registration guard in GraphTransformerManager::Register so that duplicate transformer names at the same optimization level are correctly rejected, preventing accidental double-application of the same transformer within a level.

Changes:

• Replace the dead std::find check (unique_ptr identity) with a per-level Name() uniqueness check in GraphTransformerManager::Register.
• Add a unit test validating: same name + same level is rejected, while same name + different level is allowed.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
onnxruntime/core/optimizer/graph_transformer_mgr.cc	Fixes duplicate detection by checking transformer Name() uniqueness per level before inserting.
onnxruntime/test/optimizer/graph_transform_test.cc	Adds a regression test covering duplicate-name registration behavior across levels.