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Diffstat (limited to 'chapter24/README.md')
| -rw-r--r-- | chapter24/README.md | 24 |
1 files changed, 17 insertions, 7 deletions
diff --git a/chapter24/README.md b/chapter24/README.md index 93f54a0d..a1fb6ded 100644 --- a/chapter24/README.md +++ b/chapter24/README.md @@ -298,16 +298,17 @@ both the cheaper first attempt and the mandatory fallback. Run `make spill-stats`. All rows use **Chapter 24's compiler**, optimizer seed 123, and the same source/target combinations as the earlier cohort tables. -These Windows results combine x86 SystemV/Win64 and RISC-V/ARM SystemV. +These Windows results combine x86 SystemV/Win64 and RISC-V/ARM SystemV, +remeasured on 2026-09-28 after the function-pointer lifetime backport. | Program cohort | Compilations | Split/move count | Loop-weighted count | |---|---:|---:|---:| -| Chapter 20 | 39 | 331 | 457 | +| Chapter 20 | 39 | 323 | 442 | | Chapter 21 | 52 | 436 | 975 | | Chapter 22 | 24 | 67 | 67 | -| Chapter 23 | 30 | 66 | 115 | -| Chapter 24 | 67 | 432 | 1,342 | -| **Total** | **212** | **1,332** | **2,956** | +| Chapter 23 | 30 | 84 | 231 | +| Chapter 24 | 67 | 441 | 1,400 | +| **Total** | **212** | **1,351** | **3,115** | `_spills` counts retained SplitNodes, including register moves. `_spillScaled` weights those moves by `8^loopDepth`; it is a cost estimate, not measured memory @@ -315,13 +316,15 @@ traffic. Diagnostic machine graphs contribute no allocations to this table. The reporter checks allocation legality and native/emulated results even when spill expectations differ, and exits unsuccessfully for either kind of failure. -With only the cold-first rule disabled, the same compiler and programs produce +In the original 2026-09-20 allocator audit, before subsequent compiler fixes, +the table totaled 1,332 / 2,956. With only the cold-first rule disabled, that +compiler and the same programs produced **1,338 moves / 2,962 weighted moves**. The rule saves six of each. A RISC-V MergeSort case adds one move, offset by improvements in other MergeSort cases, Sieve, and an ARM loop case. Aggregate measurements justify accepting that local regression; the improvement here is modest, not universal. -On cohorts 20-23 alone, Chapter 23 produced 933 / 1,745; Chapter 24 produces +On cohorts 20-23 alone in that audit, Chapter 23 produced 933 / 1,745; Chapter 24 produced 900 / 1,614. Only six of each reduction comes from this allocator change. The rest comes from other compiler changes, including SCCP; comparing chapters alone would overstate the heuristic's benefit. @@ -332,3 +335,10 @@ to cohort 24 alongside this chapter's existing tests. The frozen String workload also exposed a missing null check in the inlining dominator walk; that correctness fix is included on both sides of the heuristic comparison. Area/cost spill ranking remains for Chapter 25. + +The current function-pointer rule keeps unknown callers whenever an address is +used as a value rather than only as a direct call target. This preserves callable +bodies without escape analysis, but Phi-selected functions retain general +parameter types. The no-return String case now drops its unused hash bodies and +needs no splits. Source/target membership remains unchanged; these graph changes +are separate from the cold-first allocator comparison above. |