Enable ScatterElements in-place reuse when planner shape map is missing

[Copilot]

Description

ScatterElements on CPU always paid a full data -> output copy unless buffers were already aliased; in practice, planner-side MayInplace(0,0) reuse was often blocked when context shapes were unavailable (common with symbolic shapes). This change makes the reuse decision use existing NodeArg type-proto shape metadata when planner shape entries are absent.

• Planner reuse eligibility

  • Update allocation_planner.cc::SameSize(const NodeArg&, const NodeArg&):
    • Keep existing path when both context shapes exist.
    • Keep conservative behavior when only one context shape exists.
    • Add fallback when both are missing: compare tensor shapes from TypeAsProto() metadata.

• Regression coverage

  • Add PlannerTest.InPlaceTestWithTypeProtoShapeFallback in allocation_planner_test.cc.
  • Validates MayInplace reuse (kReuse) with symbolic type-proto shapes and no planner context shape entries.

if ((nullptr != p_shape1) && (nullptr != p_shape2)) {
  return SameSize(*p_shape1, arg1, *p_shape2, arg2);
}
if ((nullptr != p_shape1) || (nullptr != p_shape2)) {
  return false;
}
// both missing: fallback to TypeAsProto() tensor shapes
return SameSize(p_type1->tensor_type().shape(), arg1, p_type2->tensor_type().shape(), arg2);

Motivation and Context

ScatterData is designed to skip the copy when input/output buffers alias, but planner constraints around shape availability made that path hard to reach, especially for symbolic-shape graphs (e.g., ConstantOfShape(Shape(x)) -> ScatterElements). This change removes a planner blind spot so valid in-place reuse can be selected more often without relaxing safety checks.

• Fixes CPU ScatterElements always copies its data input, even when the producer's buffer could be reused in place #32062

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[Copilot]

Pull request overview

Attempts to enable in-place buffer reuse when planner shapes are unavailable.

Changes:

• Adds a TypeProto shape fallback.
• Adds symbolic-shape planner coverage.

Reviewed changes

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

File	Description
allocation_planner.cc	Adds shape fallback logic.
allocation_planner_test.cc	Adds fallback reuse test.

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