[AIMIGRAPHX-839] support symbolic shapes for broadcast ops

[shivadbhavsar]

Motivation

Building on top of #4702: update broadcast op compute shapes to work with symbolic shapes. Symbolic shapes also mean we no longer need to pass a 2nd input for shape reference.

Technical Details

Infrastructure

• matcher.hpp: new symbolic_shape predicate (mirrors static_shape / dynamic_shape).
• shape.hpp / shape.cpp: new shape::to_symbolic() — promotes static lens/strides to dd{sym::lit(...)} / sym::lit(...); idempotent on symbolic, throws on range-based dynamic. Centralizes "no mixing" enforcement.
• common.hpp / common.cpp: new make_bcast_shape(shape, vector<dd>) overload for symbolic targets, factored over a templated make_bcast_shape_impl shared with the static overload.

Op support (compute_shape)

• multibroadcast.hpp: 1-input symbolic mode — opt-in via fully-symbolic output_dyn_dims attribute. Static inputs bridged via to_symbolic(); range-dyn rejected.
• broadcast.hpp:
  • New output_dyn_dims attribute + 1-input symbolic mode (mirroring multibroadcast).
  • 2-input path now accepts symbolic inputs. Static s0 bridged via to_symbolic(); range-dyn + symbolic combos rejected via to_symbolic()'s throw.
  • Shared build_output lambda used by both the 1-input and 2-input symbolic paths.
• binary.hpp: symbolic inputs now fall through to the existing packed/broadcasted/permutation logic instead of throwing; routes via dyn_dims()-based with_lens / from_permutation overloads.

Compiler pass (simplify_dyn_ops)

• find_symbolic_2in_broadcasts: rewrites a 2-input broadcast / multibroadcast whose result is fully symbolic into the 1-input form by setting out_dyn_dims.
• find_symbolic_broadcast_for_dot: rewrites symbolic broadcast_for_dot into a 1-input multibroadcast with out_dyn_dims.

Changelog Category

Add a CHANGELOG.md entry for any option other than Not Applicable

• • Added: New functionality.
• • Changed: Changes to existing functionality.
• • Removed: Functionality or support that has been removed. (Compared to a previous release)
• • Optimized: Component performance that has been optimized or improved.
• • Resolved Issues: Known issues from a previous version that have been resolved.
• • Not Applicable: This PR is not to be included in the changelog.

---

[Copilot]

Pull request overview

Adds first-class symbolic-shape support for broadcast-style operators by introducing a shape::to_symbolic() conversion path, a symbolic broadcast-shape builder, and compiler-pass rewrites that canonicalize eligible 2-input broadcasts into 1-input forms carrying symbolic output dims.

Changes:

• Introduce shape::to_symbolic() and a match::symbolic_shape() predicate to enable symbolic-aware matching and shape promotion.
• Add a symbolic overload of make_bcast_shape(...) and update broadcast, multibroadcast, and binary compute-shape logic to support fully-symbolic shapes.
• Extend simplify_dyn_ops to rewrite fully-symbolic 2-input broadcast/multibroadcast and broadcast_for_dot into 1-input ops with out_dyn_dims, plus add extensive tests.

Reviewed changes

Copilot reviewed 12 out of 12 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
src/shape.cpp	Implements shape::to_symbolic() promotion logic (static → symbolic; reject range-dyn).
src/include/migraphx/shape.hpp	Declares the new to_symbolic() API.
src/include/migraphx/matcher.hpp	Adds symbolic_shape matcher predicate for symbolic output shapes.
src/common.cpp	Refactors broadcast-shape construction and adds symbolic make_bcast_shape overload.
src/include/migraphx/common.hpp	Exposes the symbolic make_bcast_shape overload and documents its contract.
src/include/migraphx/op/broadcast.hpp	Adds out_dyn_dims attribute and a symbolic 1-input mode; allows symbolic 2-input path.
src/include/migraphx/op/multibroadcast.hpp	Adds symbolic 1-input mode via fully-symbolic out_dyn_dims and bridges static inputs with to_symbolic().
src/include/migraphx/op/binary.hpp	Allows fully-symbolic inputs to flow through existing broadcast/permutation logic.
src/simplify_dyn_ops.cpp	Adds symbolic broadcast canonicalizations in simplify_dyn_ops.
test/shape_test.cpp	Adds unit tests for to_symbolic() and symbolic/static make_bcast_shape.
test/op_shape_test.cpp	Adds shape tests for symbolic binary ops and symbolic broadcast/multibroadcast modes.
test/simplify_dyn_ops_test.cpp	Adds tests covering symbolic rewrites for broadcast, multibroadcast, and broadcast_for_dot.

[codecov]

Codecov Report

❌ Patch coverage is 96.49123% with 4 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/include/migraphx/op/broadcast.hpp	96.23%	2 Missing ⚠️
src/include/migraphx/op/binary.hpp	80.00%	1 Missing ⚠️
src/include/migraphx/op/multibroadcast.hpp	95.00%	1 Missing ⚠️

Additional details and impacted files

@@                Coverage Diff                 @@
##           sym_dot_shapes    #4819      +/-   ##
==================================================
- Coverage           92.80%   92.80%   -0.00%     
==================================================
  Files                 584      584              
  Lines               30146    30169      +23     
==================================================
+ Hits                27976    27996      +20     
- Misses               2170     2173       +3     

Files with missing lines	Coverage Δ
src/common.cpp	97.46% <100.00%> (+0.14%)	⬆️
src/include/migraphx/matcher.hpp	87.57% <100.00%> (+0.04%)	⬆️
src/simplify_dyn_ops.cpp	99.40% <100.00%> (+0.03%)	⬆️
src/include/migraphx/op/binary.hpp	93.94% <80.00%> (-2.61%)	⬇️
src/include/migraphx/op/multibroadcast.hpp	97.50% <95.00%> (-2.50%)	⬇️
src/include/migraphx/op/broadcast.hpp	96.67% <96.23%> (-0.89%)	⬇️

... and 3 files with indirect coverage changes

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