Add build time optimization documentation #3608

tenpercent · 2026-01-19T19:27:24Z

Summary

Add BUILD_TIME_OPTIMIZATION.md documenting techniques for reducing C++ template instantiation overhead
Covers: O(1) pack expansion, named functors, constexpr arrays, fold expressions
Includes before/after code examples and metrics from the optimization PRs

Tracking issue: #3575

Add documentation for: - sequence_map_inverse: O(N) to O(1) via pack expansion (95% time reduction) - calculate_element_space_size: fold expression (73% time reduction) Update case studies section with these optimizations.

BUILD_TIME_OPTIMIZATION.md

shumway · 2026-01-19T22:37:39Z

include/ck/BUILD_TIME_OPTIMIZATION.md

+    {
+        return Sequence<F{}(Number<Is>{})...>{};
+    }
+    using type = decltype(make(__make_integer_seq<std::integer_sequence, index_t, N>{}));


There are two things here, the compiler intrinsic __make_integer_seq and removing the recursive generation. How much do you gain from pure C++17 standard (removing the recursion), versus full optimization with the compiler intrinsic? Is this fixed in C++2x?

As far as I can tell there's no way to switch from recursive type generation without using the intrinsic. You can check out the related LLVM and GCC issues such as this

~~__make_integer_seq is actually wrapped in std::make_integer_sequence but this is one more layer of template instantiation~~ nvm, the main problem was drift between the documentation and implementation, I updated docs with rationale for using the intrinsic

shumway · 2026-01-19T22:39:11Z

BUILD_TIME_OPTIMIZATION.md

+
+## Optimization Techniques
+
+### 1. Replace O(N) Recursion with O(1) Pack Expansion


This example is for replacing recursion with pack expansion, but it also has a compiler intrinsic. Can we split that into two different examples? I think everyone would agree with the parameter pack expansion, but considering the compiler intrinsic is a separate issue.

The compiler intrinsic doesn't exist without the parameter packs, so it's impossible to separate.

BUILD_TIME_OPTIMIZATION.md

include/ck/BUILD_TIME_OPTIMIZATION.md

BUILD_TIME_OPTIMIZATION.md

shumway · 2026-01-19T23:07:12Z

include/ck/BUILD_TIME_OPTIMIZATION.md

@@ -0,0 +1,327 @@
+# Build Time Optimization


Let's move this down into the source, where we are making the code changes. It's not customer documentation, it's aimed at the developers.

Can we align on the goal of this doc? This is kind of all over the place. If it's general info, it should probably go in the tracking bug. In fact, the cleanest way is some comments in the tracking bug that link to documented changes in the source. Then the only need for a markdown file is to track files we need to work on and what has been optimized. The scripts should be documented, so that's not needed here.

Yep, let's move to, say, include/ck

The high-level goal is to document the optimization attempts for the metaprogramming constructs that we have, as well as collect the techniques in an accessible way

When relying on the tracking issue we need to keep in mind that the source code and github infra are different sources of information; from recent discussions I had an impression we wanted to start storing the design documentation in the source, which this file would be a start for

Changes: - Move to include/ck/ (developer documentation, not customer-facing) - Add tracking issue link at top - Fix section structure (sequential numbering 1-5) - Remove mismatched transform_tensor_descriptor example - Clarify O(N) constexpr loop vs template recursion distinction - Remove "Case Studies" section (redundant with tracking issue) - Simplify examples for clarity

tenpercent requested review from a team, Snektron, ThomasNing, afagaj, andriy-ca, aosewski, asleepzzz, bartekxk, carlushuang, cgmillette, coderfeli, ddembeckAMD, geyyer, illsilin, poyenc, qianfengz, shumway, vidyasagar-amd and vpietila-amd as code owners January 19, 2026 19:27

tenpercent force-pushed the mpodkory/build-time-docs branch 2 times, most recently from b057073 to 5de5575 Compare January 19, 2026 19:37

shumway linked an issue Jan 19, 2026 that may be closed by this pull request

[Epic] Reduce CK / CKTile Build Times #3575

Open

shumway removed a link to an issue Jan 19, 2026

[Epic] Reduce CK / CKTile Build Times #3575

Open

Add build time optimization documentation

52fa8f6

tenpercent force-pushed the mpodkory/build-time-docs branch from 5de5575 to 52fa8f6 Compare January 19, 2026 21:41