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Diffstat (limited to 'chapter23/README.md')
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1 files changed, 14 insertions, 8 deletions
diff --git a/chapter23/README.md b/chapter23/README.md index 4a1118b5..c8961647 100644 --- a/chapter23/README.md +++ b/chapter23/README.md @@ -481,18 +481,24 @@ the fallback, including splitting an existing copy when all uses have the same loop depth. Cold-first loop splitting is left for Chapter 24; area/cost spill ranking remains for Chapter 25. +Chapter 21's adjacent-copy forwarding also carries forward: after coloring, +a sole use in the next instruction can read the source register when its +operand mask permits it and no two-address tie is broken. The table below +includes this cleanup. Cohort 22 now also includes the two zero-move C return +ABI checks added since the earlier audit (26 entries instead of 24). + Run `make spill-stats` in this directory. All rows below use **this chapter's compiler**, seed 123, and frozen source/target combinations from each cohort. The Windows run combines x86 SystemV/Win64 and RISC-V/ARM SystemV. Diagnostic machine graphs are checked separately and do not contribute to the counts. -| Program cohort | Compilations | Split/move count | Loop-weighted count | +| Program cohort | Compilations | Retained moves | Loop-weighted moves | |---|---:|---:|---:| -| Chapter 20 | 39 | 332 | 458 | -| Chapter 21 | 52 | 450 | 989 | -| Chapter 22 | 24 | 67 | 67 | -| Chapter 23 | 30 | 84 | 231 | -| **Total** | **145** | **933** | **1,745** | +| Chapter 20 | 39 | 326 | 445 | +| Chapter 21 | 52 | 439 | 971 | +| Chapter 22 | 26 | 67 | 67 | +| Chapter 23 | 30 | 81 | 228 | +| **Total** | **147** | **913** | **1,711** | `_spills` counts retained SplitNodes, including register moves; `_spillScaled` weights them by `8^loopDepth`. These estimate compiler-generated moves, not @@ -500,7 +506,7 @@ runtime memory traffic. The reporter prints individual compilations and sums by CPU/ABI, and still reports failure when a spill expectation or execution check fails. -With grouping disabled and everything else held fixed, this suite produces +In the earlier audit, before adjacent-copy forwarding, disabling grouping produced **the same 933 moves / 1,745 weighted moves**. The original grouping code also has those totals. This suite therefore shows no spill improvement from grouping; the reduced machine-graph regression exercises its compatibility and call rules, @@ -508,7 +514,7 @@ including a null-mask crash in the old implementation. A plausible allocator heuristic needs measurements on workloads that reach it before claiming a win. For the older cohorts alone, Chapter 22's compiler produced 838 moves / 1,496 -weighted moves; this compiler produces 849 / 1,514. That comparison includes +weighted moves; this compiler then produced 849 / 1,514. That comparison includes changes outside allocation. In particular, Chapter 20's frozen String input survives optimization here and costs 16 weighted moves; Chapter 22 eliminated it at this seed. It would be misleading to attribute that difference to grouping. |