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diff --git a/chapter20/README.md b/chapter20/README.md index e11dcff2..9f7cb1c5 100644 --- a/chapter20/README.md +++ b/chapter20/README.md @@ -503,59 +503,25 @@ two-address operands, and Phi register agreement; tiny machine graphs exercise hard conflicts independently of optimizer choices. Native execution comes with encoding in Chapter 21. -### Spill-count summed across tests - -Run `make spill-stats` to execute the tests and print each compilation's counts, -CPU/ABI subtotals, and the total below. Assertions remain enabled, and a failing -test makes the command fail. The optimizer's default seed is 123. - -The Chapter 20 program cohort is all 11 source examples in `Chapter20Test`, plus -`BrainFuckTest.testBrainfuck` and `MergeSortTest.testMergeSort`, on x86-64, -RISC-V, and ARM using SystemV: 13 programs and 39 compilations, including the -zero-spill cases. The synthetic allocator regression graphs are correctness -checks, not additional program benchmarks. - -| Program-test cohort | Allocator chapter | Compilations | Split moves | Loop-weighted moves | -|---|---:|---:|---:|---:| -| Chapter 20 | 20 | 39 | 234 | 360 | - -`_spills` counts surviving split moves, including register-to-register copies; -it does not count only stack stores. `_spillScaled` weights each move by -`8^loopDepth`, a rough cost estimate rather than measured execution frequency. -The weighted subtotals are 161 for x86-64, 100 for RISC-V, and 99 for ARM. - -### Comments on the measurements - -Before the correctness fixes, this cohort had 235 moves / 354 weighted moves. -The corrected baseline before lazy memory cost three more of each. The final narrow x86 -store-mask backport accounts for two of those moves: an integer byte/short store -cannot consume an XMM register. This is a correctness cost, not a quality gain. -The fixed-neighbor color-bias correction changes no counts in this cohort. - -With lazy memory and selected-read ordering, the same 39 compilations have -234 moves / 360 weighted moves, versus 238 / 357 before the port. Register -legality passes on every target; allocator heuristics are unchanged. The changed -programs are: - -| Program | Target | Moves before / after | Weighted before / after | -|---|---|---:|---:| -| Array access (`testAlloc2`) | x86-64 | 1 / 2 | 1 / 2 | -| Array prefix sum (`testArray1`) | x86-64 | 5 / 6 | 5 / 13 | -| String hash | x86-64 | 7 / 5 | 21 / 19 | -| String hash | RISC-V | 4 / 3 | 4 / 3 | -| String hash | ARM | 5 / 3 | 5 / 3 | -| Merge sort | ARM | 37 / 36 | 37 / 36 | - -The prefix sum's extra loop move follows from scheduling selected reads before -clobbering writes. A diagnostic build omitting that ordering returns to 5 / 5; -it is not a valid alternative schedule. These are changed frontend and scheduling -graphs, not a comparison of allocator heuristics. The new memory-allocation -regressions check legality but do not add entries to this measured cohort. - -Later chapters will add one quality technique at a time and end with this kind -of table: Chapter 21 will measure both the Chapter 20 and Chapter 21 program -cohorts using its allocator, and Chapter 25 will have rows for cohorts 20-25. -Keep the program/target membership and seeds fixed when comparing a row between -chapters, and separate changes in the optimizer or instruction selection from -changes in allocation. A local regression may be worthwhile when the total -improves; an allocation failure or illegal register assignment never is. +Rows are fixed test cohorts; columns are the compiler/allocator chapters. +Each cell is the sum of `_spillScaled`: retained split moves, including register +copies, weighted by `8^loopDepth`. Lower is better. **# tests counts compilations** +(program/CPU/ABI cases), including zero-spill cases, rather than JUnit methods. +The count and membership of each row stay fixed across columns. + +<!-- spill-matrix:start --> +| Test cohort | # tests | Ch 20 | +|---|---:|---:| +| Ch 20 | 39 | 360 | +<!-- spill-matrix:end --> + +These Windows measurements use optimizer seed 123 for cohorts 20-24 and include +x86-64 SystemV/Win64 and ARM/RISC-V SystemV as applicable. Run `make spill-stats` +here for this compiler, or at the repository root to rebuild the full matrix +and check cohort membership. See the [complete comparison](../docs/regalloc-spills.md) +for measurement details and reproduction commands. + +Cohort 20 contains 11 Chapter20Test programs plus BrainFuck and MergeSort, +each on three SystemV targets: 39 compilations. Synthetic allocator graphs +check correctness separately. This is the baseline; later chapters extend the +columns while keeping these programs and targets fixed. |