Add generate_identity_sequences helper and replace lambdas with named functors

[tenpercent]

Summary

• Add generate_identity_sequences<N>() helper that returns Tuple<Sequence<0>, Sequence<1>, ..., Sequence<N-1>>
• Replace lambdas with named functors in transform_tensor_descriptor
• Add unpack_and_merge_sequences helper functor
• Reduces transform_tensor_descriptor instantiations from 388 to 32 (92% reduction)

Motivation

Multiple call sites use generate_tuple([](auto i) { return Sequence<i>{}; }, Number<N>{}) pattern. A named helper reduces lambda instantiations.

Additionally, each lambda in transform_tensor_descriptor creates a unique closure type, causing the function to be instantiated separately for every call site. Named functors share a single type, so the compiler reuses the same instantiation.

Changes

Part 1: generate_identity_sequences helper

• Replaces common lambda pattern for generating identity sequences
• Each lambda expression creates a unique closure type, causing separate template instantiations at every call site
• Named helper shares a single type across all uses

Part 2: Named functors in transform_tensor_descriptor

• Add unpack_and_merge_sequences helper to replace lambda in GetNumOfHiddenDimension
• Use generate_identity_sequences in matrix_padder.hpp

Test Plan

• Added 7 unit tests:
  • 4 tests for generate_identity_sequences
  • 3 tests for unpack_and_merge_sequences
• Waiting for full CI

Related PRs

This PR merges the functionality from:

• Add generate_identity_sequences helper for common pattern #3588 (generate_identity_sequences helper)
• Replace lambdas with named functors in transform_tensor_descriptor #3589 (Named functors in transform_tensor_descriptor)

Part of PR stack for issue #3575 (Reduce CK/CKTile Build Times)

Note: This PR supersedes #3588 and #3589, which can be closed once this is merged.

[Copilot]

Pull request overview

This PR aims to reduce C++ template instantiations (and improve build times) by introducing reusable helpers for common sequence/tuple metaprogramming patterns and by replacing per-call-site lambdas with named functors.

Changes:

• Added generate_identity_sequences<N>() helper to generate Tuple<Sequence<0>, ..., Sequence<N-1>> without lambdas.
• Added named sequence utilities (merge_sequences_functor, unpack_and_merge_sequences) and replaced lambdas in transform_tensor_descriptor/TensorDescriptor logic.
• Updated multiple call sites to use the new helper(s) and added unit tests.

Reviewed changes

Copilot reviewed 18 out of 18 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
test/util/unit_sequence_helper.cpp	Adds unit tests for generate_identity_sequences and unpack_and_merge_sequences.
test/util/CMakeLists.txt	Adds a new gtest executable target for the new unit tests.
include/ck/wrapper/utils/tensor_partition.hpp	Switches identity-dimension tuple generation to generate_identity_sequences.
include/ck/wrapper/utils/layout_utils.hpp	Switches identity-dimension tuple generation to generate_identity_sequences.
include/ck/wrapper/tensor.hpp	Switches identity-dimension tuple generation to generate_identity_sequences.
include/ck/wrapper/operations/gemm.hpp	Switches identity-dimension tuple generation to generate_identity_sequences.
include/ck/wrapper/layout.hpp	Switches identity-dimension tuple generation to generate_identity_sequences.
include/ck/utility/tuple_helper.hpp	Introduces generate_identity_sequences helper implementation.
include/ck/utility/sequence_helper.hpp	Introduces named functors and unpack_and_merge_sequences.
include/ck/tensor_operation/gpu/thread/threadwise_tensor_slice_transfer_v7r3_scatter.hpp	Replaces identity sequence generation lambda with generate_identity_sequences.
include/ck/tensor_operation/gpu/thread/threadwise_tensor_slice_transfer_v7r3.hpp	Replaces identity sequence generation lambda with generate_identity_sequences.
include/ck/tensor_operation/gpu/thread/threadwise_tensor_slice_transfer_v7r2.hpp	Replaces identity sequence generation lambda with generate_identity_sequences.
include/ck/tensor_operation/gpu/thread/threadwise_tensor_slice_transfer_v3r2.hpp	Replaces identity sequence generation lambda with generate_identity_sequences.
include/ck/tensor_operation/gpu/thread/threadwise_tensor_slice_transfer_v3r1_gather.hpp	Replaces identity sequence generation lambda with generate_identity_sequences.
include/ck/tensor_operation/gpu/thread/threadwise_tensor_slice_transfer_v3r1_dequant.hpp	Replaces identity sequence generation lambda with generate_identity_sequences.
include/ck/tensor_operation/gpu/thread/threadwise_tensor_slice_transfer_v3r1.hpp	Replaces identity sequence generation lambda with generate_identity_sequences.
include/ck/tensor_operation/gpu/device/matrix_padder.hpp	Replaces identity sequence generation lambda with generate_identity_sequences.
include/ck/tensor_description/tensor_descriptor.hpp	Replaces lambdas with named functors and uses unpack_and_merge_sequences.

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[tenpercent]

one thing to consider is whether those new helper functors are the implementation detail and not the part of the header interface

[ammallya]

Imported to ROCm/rocm-libraries