diff options
Diffstat (limited to 'skills')
| -rw-r--r-- | skills/chapter25-codex-notes.md | 35 |
1 files changed, 35 insertions, 0 deletions
diff --git a/skills/chapter25-codex-notes.md b/skills/chapter25-codex-notes.md index 4fb182ff..b38d1c29 100644 --- a/skills/chapter25-codex-notes.md +++ b/skills/chapter25-codex-notes.md @@ -121,6 +121,41 @@ lessons rather than duplicating that history. recursive calls keep this regression meaningful. Check all chain members, registered data edges, and one shared copy per function. +## Register allocation review + +- Allocation starts in 20; native encoding in 21. Backport legality and + no-progress fixes to the first applicable chapter, but introduce spill-quality + heuristics gradually. Do not import the complete Chapter 25 allocator into 20. + Printing, deterministic ordering, and diagnostic support may start in 20. +- Compare measured spill totals over the same tests, targets/ABIs, and seeds. + Local increases are acceptable when offset elsewhere; report per-target and + overall totals. `_spills` counts surviving SplitNodes, and `_spillScaled` + weights those moves by `8^loopDepth`; neither means only memory stores. +- Separate allocation completion/register legality/runtime results from quality + expectations. Reaching the round limit is a correctness bug; raising the + limit or changing spill goldens does not prove progress fixed. Heuristics + which defer necessary splitting must retain a bounded fallback. +- Review the README with each allocator chapter. End it with a RegAlloc + improvements section, a measured table, and commentary. Each row names a + program cohort, all compiled by that directory's compiler: 20 in Chapter 20, + 20-21 in Chapter 21, through 20-25 in Chapter 25. Include the BrainFuck and + MergeSort allocator cases in the Chapter 20 cohort (39 compilations, not just + Chapter20Test's 33). Keep diagnostic machine graphs separate from quality data. +- `make spill-stats` starts in 20. Helpers explicitly name the program cohort; + the JUnit listener labels individual cases and sums CPU/ABI and cohort totals. + Assertions stay enabled and failures propagate. Do not silently change cohort + membership, seeds, or targets when comparing chapters. +- Chapter 20's corrected baseline costs one extra weighted move (354->355 over + 39 compilations); document this as a correctness cost. Advanced quality + heuristics remain staged. Stop after 20 for Cliff's review. When reaching 21, + shorten its excessive encoding detail as requested. +- Copy cleanup/reuse must check kill masks even when an instruction has no LRG; + before coloring, a fixed-register definition can clobber despite `_reg==-1`. + Cloning is valid only if its output mask can satisfy the use. A fixed-register + clone with flexible uses needs use-side splits, not a no-op def-side path. +- The staged plan and historical fix inventory are in + `docs/chapter-backports.md`; its review is not evidence of completed backports. + ## Null guards: B13 / issue #246 lessons - Null refinement starts in Chapter 10; arrays in 15; scoped expression guards |