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[CK_TILE] Flatten nested static_for loops into static_ford (#5939) MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit ## Summary Mechanical conversion of 129 nested `static_for`/`static_ford` patterns to flat `static_ford` across 29 ck_tile header files. Each conversion eliminates intermediate lambda closure instantiations by replacing nested compile-time loops with a single flat iteration using index decomposition. ### What `static_ford` eliminates When `static_for` loops are nested, each level creates unique closure types: ```cpp // BEFORE: M + M×N = 20 IR functions (for M=4, N=4) static_for<0, 4, 1>{}([&](auto m) { // 4 closure instantiations static_for<0, 4, 1>{}([&](auto n) { // 4×4 = 16 closure instantiations body(m, n); }); }); // AFTER: M×N = 16 IR functions (with ford_applier, no intermediates) static_ford<sequence<4, 4>>{}([&](auto mn) { constexpr auto m = number<mn[number<0>{}]>{}; constexpr auto n = number<mn[number<1>{}]>{}; body(m, n); }); ``` ### Pattern categories converted | Category | Count | Description | |----------|-------|-------------| | C (2-level `static_for` chains) | 112 | Nested `static_for` → `static_ford` | | C3 (3-level `static_for` chains) | 9 | Three consecutive nests → `static_ford` | | Partial rescue | 3 | Outer 2 levels of blocked 4-level nests | | B (nested `static_ford` merge) | 5 | Two nested `static_ford` → single higher-dim `static_ford` | | **Total** | **129** | Across 29 files | 6 false positives were detected and reverted (in `tensor_adaptor.hpp`, `tile_distribution.hpp`, `tile_distribution_encoding.hpp`) where the inner loop bound depended on the outer variable. ### Files changed by family | Family | Files | Sites | |--------|-------|-------| | Block GEMM | 12 | ~20 | | FlatMM pipelines | 4 | ~69 (including 5 ford-ford merges) | | GEMM quant | 7 | ~22 | | FlatMM kernel | 1 | 2 | | FMHA | 1 | 2 | | Reduce/norm | 2 | 2 | | Epilogue | 1 | 1 | ### Blocked locations from review comments - **block_gemm_areg_breg_creg_v1.hpp:356** — BLOCKED: runtime scale loads (`scale_a_slice`, `scale_b_slice`, A warp tensor load) between every nesting level - **block_universal_gemm_ar_aquant_flatbr_bquant_cr.hpp:228** — BLOCKED: `zero_accumulators()` before inner loop; `sched_barrier` + conditional `block_sync_lds()` after inner loop - **block_universal_gemm_as_aquant_bs_bquant_cr.hpp:298** — BLOCKED: runtime `CWarpTensor` construction before inner loop; quantization scale application code after inner loop - **block_universal_gemm_as_aquant_bs_cr.hpp:277** — BLOCKED: same pattern as above - **block_universal_gemm_as_bs_bquant_cr.hpp:367** — BLOCKED: same pattern as above ## Depends on - #5938 ([CK_TILE] Optimize static_ford and sequence compile-time infrastructure) — provides the `ford_applier` that makes these conversions beneficial. Without it, `static_ford` uses a recursive implementation that provides no IR function savings. ## Results (combined with #5938) ### Build Time (Wilcoxon signed-rank, 7 paired trials, gfx942) | Target | Base (s) | Treat (s) | Delta | % | Significant? | |--------|----------|-----------|-------|---|-------------| | **flatmm** | 161.1 | 149.0 | **-12.1s** | **-7.5%** | **YES** (p<0.01, 7/7 wins) | | **universal_gemm** | 225.4 | 220.3 | **-5.1s** | **-2.3%** | **YES** (p<0.01, 7/7 wins) | ### IR Function Counts (device trace, gfx942) | Target | InstFunc | CodeGen | |--------|----------|---------| | universal_gemm | **-8.5%** | **-9.2%** | | flatmm | **-7.6%** | **-10.5%** | ### ASM Equivalence 5/5 PASS — 650,151 lines verified identical (gfx942). TUs: universal_gemm, flatmm_basic, fmha_bwd, reduce, bscale. ## Test plan - [x] ASM equivalence verified (650K lines, gfx942) - [x] Wilcoxon timing verified (7 trials, p<0.01) - [x] IR function counts verified (-7.6% to -10.5% CodeGen reduction) - [ ] CI 🤖 Generated with [Claude Code](https://claude.com/claude-code)