Replace nested static_for lambdas with compile-time search helper #3600
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This was referenced Jan 16, 2026
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The GetTransformAndItsUpperDimension function used nested static_for loops with lambdas to search for a hidden dimension in UpperDimensionIdss. This caused 918 applier::operator() instantiations (81% of all applier instantiations). Replace with find_in_tuple_of_sequences helper that uses constexpr array lookup and if-constexpr recursion, eliminating the lambda instantiation overhead. Results on example_grouped_conv_fwd_xdl_fp16: - applier instantiations: 1132 -> 127 (89% reduction) - TensorDescriptor instantiations: 2503 -> 664 (73% reduction) - Template instantiation time: 23.4s -> 19.4s (17% reduction)
…tSize The InitializeElementSize function used generate_tuple with a lambda to compute visible dimension lengths. Each TensorDescriptor type created a unique lambda type, causing 78 instantiations (385ms). Replace with direct pack expansion using helper functions, eliminating the lambda instantiation overhead entirely. Results on example_grouped_conv_fwd_xdl_fp16: - generate_tuple lambdas: 178 -> 100 (44% reduction) - Template instantiation time: 19.5s -> 19.0s
TensorAdaptor has identical InitializeElementSize and GetTransformAndItsUpperDimension patterns as TensorDescriptor. Apply the same optimization: - Replace nested static_for lambdas with find_in_tuple_of_sequences - Replace generate_tuple lambda with pack expansion Results: generate_tuple lambdas 100 -> 96 (4 events, 17ms eliminated)
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Detailed comments explain: - sequence_find_value: Constexpr loop with O(1) template depth vs O(N) recursive - find_in_tuple_of_sequences: Pack expansion instead of nested static_for loops - Why constexpr search reduces template instantiations dramatically - When to apply constexpr search patterns for compile-time operations - Implementation details for each optimization approach This documentation helps maintainers understand the compile-time search optimization strategy without relying on specific benchmark numbers that may vary by use case.
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Summary
find_in_tuple_of_sequencescompile-time search helper with O(1) template depthstatic_forlambdas inTensorDescriptor::GetTransformAndItsUpperDimensiongenerate_tuplelambda inTensorDescriptor::InitializeElementSizewith pack expansionTensorAdaptorMotivation
The
TensorDescriptorandTensorAdaptorclasses had excessive template instantiation from:static_forloops with lambdas (918applier::operator()instantiations)generate_tuplewith lambdas (78+ instantiations per class)Why It Works
Each lambda creates a unique closure type, causing separate instantiations at every call site. The
find_in_tuple_of_sequenceshelper uses O(1) template depth via pack expansion instead of O(N) nestedstatic_forrecursion, and named functors share a single type across all uses.Results (example_grouped_conv_fwd_xdl_fp16)
applierinstantiationsgenerate_tuplelambdasTest Plan
sequence_find_valuefind_in_tuple_of_sequencesPR Stack
This PR is part of the build time optimization effort (issue #3575). All PRs now target develop independently:
__make_integer_seqTracking issue: #3575