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diff --git a/docs/chapter-backports.md b/docs/chapter-backports.md index 159bc9e6..b2fe0381 100644 --- a/docs/chapter-backports.md +++ b/docs/chapter-backports.md @@ -12,6 +12,61 @@ establish the review workflow. No renumbering is committed. Keep each correction's reduced failure, smallest patch, and test results together for review. +## Follow-ups exposed by the Chapter 22 allocator review + +- **Narrow-store register masks:** fixed locally in 22-24, with + `Chapter21Test.testNarrowStores`. Bring the x86 restriction to 20-21, + and the RISC-V restriction to 21; 19's masks and 20's RISC-V mask are + already general-register-only, and 25 already has both fixes. Byte/short stores + cannot consume XMM/FPR values. The old x86 `_sz >= 2` compares a character to + an integer and always accepts XMM; the intended threshold is `'4'`. RISC-V + previously accepted its full memory mask for every width. With Chapter 21's + bias in 22, `testSextSuccess` emitted an invalid FP byte store on RISC-V and + asserted in `StoreX86.encVal` on x86. Preserve cohort data when backporting: + correcting a mask can substantially change spill counts even without tuning. +- **FunPtrNode backport: defer until register allocation work is complete.** The + minimal reproducer is `return {->42;};`; `return sys.io.p;` fails for the same + reason. Both fail on x86, RISC-V, and ARM at the default seed 123. The first + iterative Opto pass preserves the target. The subsequent pruning loop in + `CodeGen.opto` equates no linked calls with no callers for anonymous and `sys.` + functions, clears their unknown-caller Start edge, and deletes their bodies. + Their function-address ConstantNodes have no edge to keep the bodies alive. + The returned pointer survives while its Return disappears from Stop. + + Instruction selection resets NIDs and never selects the deleted function, so + the linker still maps its pointer to an ideal FunNode. In the reduced anonymous + case that node is 256; the x86 machine graph has UID 19. `Encoding.relo` accepts + the stale target and `patchLocalRelocations` indexes `_opStart[256]`. Enlarging + the array would merely hide a missing function body and produce a wrong address. + + `val f = {->42;}; return f;` retains the named function and encodes on all three + targets. An isolated build that excludes anonymous functions from pruning also + encodes both anonymous reproductions, confirming the cause; it does not fix + escaped `sys.` addresses. Cliff's chosen direction is to investigate backporting + Chapter 25's `FunPtrNode`, whose edge to the function Return keeps the function + body alive. This supersedes the proposed address-reference scan. Leave both + examples as documented known failures while finishing the allocator chapters; + do not fold this reachability change into that work. + + After register allocation, find the earliest applicable chapter and carry the + function-pointer representation and its retention rules together: pointer + creation, Opto's unknown-caller pruning, instruction selection, global constant + cloning, and relocation must agree on the retained function. Adapt these to + each chapter without importing unrelated Chapter 25 module/escape machinery. + Validate a returned pointer by calling it, and cover library pointers and + genuinely unused helpers. Chapter 21 lacks this pruning pass and also treats a constant-only + default main differently, so its old encoding-only coverage was not equivalent. + Diagnostic logs are in `chapter22/build/funptr-review`; the reduced sources and + causal trace above are the durable reproduction. +- **String without an explicit return in 22:** use the unchanged source in + `Chapter20Test.testString`, with the same driver and seeds 0-29. All three CPUs + fail before allocation, in loop-tree construction or GCM (missing loop owner, + dead CallEnd, or a FunNode cast to LoopNode, depending on seed). The original + snapshot reproduces the same 90 failures; seed 123 folds the work away. Reduce + this around Chapter 22's default-return/dead-call handling before changing a + central reachability invariant. Do not count a different seed or added return + as fixing this input. + ## AOT class initialization: larger independent work Proposed on 2026-09-19; deferred behind the smaller BXX cleanup above. This is @@ -69,7 +124,7 @@ Chapter 25 suite, including `make -j 4 tests`. | Group | Eventual home | Why not in the small queue yet | |---|---|---| -| Register allocation and spilling | 20 onward | Chapters 20-21 correction/support passes complete locally; review Chapter 21 statistics before Chapter 22. Staged quality work remains below. | +| Register allocation and spilling | 20 onward | Shared corrections/support now carried through 25; staged allocator/cohort/README reviews are complete through 22, with 23 next. | | Conditional Store and array Load control | Memory/arrays chapters | Reproduce under the earlier alias model before extracting fixes from the new memory implementation. | | SCCP dependencies, function revival, reachability | 24; some foundations may fit 18 | Separate old-IR corrections from new Guard/Escape/BulkMemPhi and external-caller machinery. | | TypeScalar, numeric modes, guards, symbolic fields, open/forward types | Revisit earlier homes later | A connected incomplete-types architecture, including phase ordering and errors. | @@ -78,9 +133,10 @@ Chapter 25 suite, including `make -j 4 tests`. ## Register allocation: correctness first, staged improvements -Review on 2026-09-20. The staged plan follows; Chapters 20-21 -have since been implemented and validated as recorded below. Later snapshots -remain pending. Compared RegAlloc, BuildLRG, IFG, +Review on 2026-09-20. The staged plan follows; Chapters 20-22 +have since been implemented and validated as recorded below. Shared corrections +and test support have also been carried through 23-25; their quality/cohort/README +reviews remain pending. Compared RegAlloc, BuildLRG, IFG, LRG, Coalesce, RegMask, and split support across 20-25, with the original fix commits. Allocation starts in 20; 19 has instruction selection/register masks but no coloring allocator. Most changes are in 20->21 and 24->25. The 22->23 @@ -139,6 +195,13 @@ to add persistent deferral state to the first allocator chapter. - Record actual `_spills` and `_spillScaled` for each compilation, keyed by test, CPU, ABI, and fixed seed. Both count retained SplitNodes; `_spillScaled` weights each by `8^loopDepth`. These are move/split metrics, not solely memory traffic. +- Use one fixed optimizer seed for routine backend validation. Seeds shuffle + IterPeeps/Opto worklists, whose output should normalize modulo NIDs and equivalent + operand orderings; similar post-Opto graphs give little additional allocation, + scheduling, or encoding coverage. Reserve seed sweeps for optimizer/worklist + investigations or demonstrated order-sensitive failures. Inspect post-Opto + differences before multiplying backend runs. Prefer varied programs, register + constraints, targets/ABIs, and execution checks for allocator coverage. - Compare total scaled counts as the existing quality measure, and report raw totals plus the largest local changes. Report per CPU/ABI as well as the whole suite so a regression on one target is visible. Include compilations without @@ -153,14 +216,14 @@ to add persistent deferral state to the first allocator chapter. of the heuristic's exact spill count. - `splitBypass` originally scanned from `j-1` with `idx++` throughout 20-25, reaching its own destination and rejecting nonadjacent bypasses. Corrected - in 20-21 with intervening kill-mask checks and a regression; 22-25 remain pending. + through 25 with intervening kill-mask checks and a regression. Pre-color copy reuse also checks fixed-register definitions before they have an assigned `_reg`. Chapter 25 is not a complete correctness reference. Suggested execution order: support/measurement, small mask/LRG correctness fixes, constrained-register and self-conflict regressions/fixes, then one quality technique at a time. Run each affected snapshot's full suite at each -accepted boundary. Chapters 20-21 have now been implemented; stop for Cliff's review before 22. +accepted boundary. Chapters 20-22 have now been implemented; stop for Cliff's review before 23. Review each chapter's README along the way. Chapter 21's encoding discussion has been shortened, with the bit-level notes retained as a separate reference. End each README with its RegAlloc improvement, measured cohort table, and commentary; the Chapter 25 @@ -206,6 +269,66 @@ Historical results below are dated evidence, not a substitute for a fresh baseline. Logs live in ignored build directories and may no longer exist. Reusable implementation lessons are in `skills/chapter25-codex-notes.md`. +### Shared allocator fixes/support: forwarded through 25, 2026-09-20 + +At Cliff's request, carried the common Chapter 22 corrections into 23-25 in +this review batch, avoiding repeated chapter-by-chapter review of the same +changes. Preserved each later allocator's existing grouping, split-delay, and +area/cost choices; the staged quality/cohort/README reviews still resume at 23. + +The shared packet includes bounded register-mask iteration and nonempty +single-bit tests; commutative BuildLRG output fallback/null masks; resultless +kill handling; fixed-register clone progress; null sample/traversal guards; +and backward copy bypass with kill masks and uncolored fixed definitions. +Chapters 23-24 also receive the corrected clone adjacency/multiple-use test, +narrow-store masks, and native process exit-status assertions. Chapter 25 +already has the store/exit-status fixes and retains its module-aware verifier. + +Forwarded all eight RegAllocTestSupport diagnostic groups and Chapter20Test/ +Chapter21Test hooks. Generic allocation, encoding, native, and emulator helpers +use CheckedCodeGen, whose regAlloc override checks function ownership, register +masks, two-address constraints, and Phis immediately after allocation. Encoding +adds untyped branches and rewrites tail calls, so running these checks afterward +is too late: even Call.regmap may consult CFG.fun. This test-only hook preserves +25's driver serialization/import-unlink ordering. Chapter 22 uses the same hook. + +Unmodified destination baselines passed. Against their saved main classes, +five diagnostic groups fail in 23/24 (masks, resultless kills, clone progress, +commutative Phi fallback, copy clobbers), and three fail in 25 (masks, clone +progress, copy clobbers). All eight pass in all three corrected destinations. +Final `make -j 4 tests` passes 23: 428 + 1 fuzzer, 24: 451 + 1 fuzzer, +and 25: 459 tests across all six groups (8 + 386 + 34 + 18 + 1 + 12). +Chapter 22 still passes 416 + 1 fuzzer; its separate `make spill-stats` passes +55 tests / 115 allocations with the unchanged 838 raw / 1,496 weighted total. + +For this common-fix comparison, froze each destination's existing local program +suite and default seed. Included its Chapter20-24 allocator/native cases as +applicable, BrainFuck, and MergeSort; excluded diagnostic graphs/new regressions. +These are within-chapter before/after comparisons, not the historical cohort +rows needed for the later README reviews. In particular, 25's module suite is +covered by the full tests, not included in these spill sums. + +| Compiler / same local suite | Allocations | Raw before | Raw after | Weighted before | Weighted after | +|---|---:|---:|---:|---:|---:| +| 23 | 119 | 629 | 614 | 1,511 | 1,279 | +| 24 | 174 | 968 | 953 | 2,620 | 2,381 | +| 25 | 146 | 660 | 656 | 1,255 | 1,244 | + +| Compiler | ARM weighted | RISC-V weighted | x86 SystemV weighted | x86 Win64 weighted | +|---|---:|---:|---:|---:| +| 23 | 413 -> 343 | 417 -> 345 | 95 -> 95 | 586 -> 496 | +| 24 | 643 -> 573 | 647 -> 575 | 95 -> 95 | 1,235 -> 1,138 | +| 25 | 348 -> 347 | 346 -> 343 | 123 -> 114 | 438 -> 440 | + +Changed goldens only after measuring the aggregate: in 23/24, NewtonInteger +Win64 55 -> 48, Sieve Win64 257 -> 186 / RISC-V 160 -> 92 / ARM 160 -> 94, +and arg_count Win64 42 -> 32. In 25, NewtonFloat SystemV 48 -> 40 and arg_count +Win64 31 -> 35. That local increase is accepted against the overall reduction. +All measured cases now complete their legality, quality, native/emulator checks: +53 tests in 23, 77 in 24, and 67 in 25. Logs, original classes, and disposable +measurement sources are under each chapter's `build/forward-regalloc`. +The separate FunPtrNode reachability backport remains deferred as requested. + ### Inlined return typing and ARM emulator: corrected, 2026-09-20 The ARM seed-9 String failure was an optimizer bug: inlining can delete a FunNode @@ -235,6 +358,83 @@ Fresh baselines passed before edits. Full suites after correction: 20: 376+1; are excluded from spill measurements. Logs/reducers are in each affected chapter's ignored `build/arm-top`; the earlier chapter-by-chapter allocator review gate remains. +### Chapter 22 allocator: ready for review, 2026-09-20 + +Carried forward the corrected Chapter 21 allocator and its diagnostic checks, +retaining native frame/call support (`CallEndMach` in 22). Five inherited +regressions fail against the original 22 classes: mask iteration/empty masks, +resultless register kills, fixed-register clone progress, commutative Phi fallback, +and copy bypass across clobbers. All eight diagnostic groups pass now. + +Chapter 22 keeps the stronger copy-chain and loop-backedge color bias, and cheap +cloneable/callee-save spill ordering. Cloneable candidates must have samples; +coalescing can leave either absent. The adjacent-use test now compares +`defIndex+1 < useIndex`, not `defIndex < useIndex+1`, and treats multiple uses +explicitly. Popular-use grouping is removed for introduction in 23; cold loop +split deferral and area/cost ranking remain for 24 and 25. + +The native test helper had lost its exit-status assertion. Restored checking of +its full integer exit code; `testNativeExitStatus` proves an empty-output program +returning 7 fails. `testNarrowStores` first failed against the old RISC-V mask, +then against the old x86 mask; both now reject FP registers for byte/short stores, +and signed/unsigned RISC-V byte/short writes execute with the expected bytes. +These restrictions already exist in 25; remaining destinations are queued above. + +Preserved cohorts 20 and 21 rather than silently accepting changed inputs: +`person21` holds the original 64-bit age example, and `testInfiniteReturn` belongs +to 22 while the old loop remains in 21. Cohort 22 includes its new allocation +programs and repeated encoding/emulator compilations; diagnostic tests stay out. + +| Cohort, all using Chapter 22 | Compilations | Original splits | Current splits | Original weighted | Current weighted | +|---|---:|---:|---:|---:|---:| +| Chapter 20 | 39 | 322 | 324 | 448 | 443 | +| Chapter 21 | 52 | 465 | 447 | 1,221 | 986 | +| Chapter 22 | 24 | 67 | 67 | 67 | 67 | +| **Total** | **115** | **854** | **838** | **1,736** | **1,496** | + +The original full suite passed 399 tests plus the fuzzer. Its frozen-cohort run +completed all 115 allocations and execution checks, with 15 differences from +Chapter 21's spill expectations. The final `make -j 4 tests` passes 416 tests plus +the fuzzer; `make spill-stats` passes 55 tests, 115 allocations, and all quality, +register-legality, function-ownership, native, and emulator checks. Sources and +expectations were force-recompiled before checking. The README ends with the +cohort table and explains the metrics; its FFI examples now match `sys.smp`. + +A controlled ablation substitutes only Chapter 21's IFG bias/ordering, keeping +all other code and the new narrow-store restrictions fixed. It completes all +115 allocations and runtime checks: 885 splits / 1,543 weighted, versus 838 / +1,496 with the new preferences, a 47 weighted move (3.0%) improvement. The scratch +ablation expects 42 instead of 41 bytes for the x86 narrow-store example because +its chosen registers need an extra REX byte; runtime and mask checks remain on. +Quality differences are reported with nonzero exit status, not suppressed. + +| Target/ABI, all cohorts | Compilations | Chapter 21 preferences, weighted | Chapter 22 preferences, weighted | +|---|---:|---:|---:| +| x86 SystemV | 22 | 267 | 268 | +| x86 Win64 | 15 | 414 | 415 | +| RISC-V SystemV | 39 | 437 | 407 | +| ARM SystemV | 39 | 425 | 406 | + +Against the controlled ablation, BrainFuck saves 14 on RISC-V and 6 on ARM in +both cohorts; ARM `testAlloc2` saves 4. Several MergeSort variants and RISC-V Sieve +increase by one. Against the original mixed snapshot, Sieve saves 72 weighted +moves on each target and Win64 argCount saves 10. This shows why individual spill +goldens are reviewed against the aggregate rather than requiring every case to +improve. Chapter totals also reflect lowering: the frozen String example has no +explicit return and folds away at seed 123 in 22. + +The supplementary 13-program, three-target, 30-seed encoding sweep completes +990 of 1,170 compilations with register checks. The remaining 180 fail on String +(before allocation) and FltArg (relocation); the original classes reproduce all +180 and additionally fail five allocator diagnostic groups per seed. No new +program failures were introduced by the allocator work. The two source-level +failures are queued above, not hidden by changing inputs, seeds, or expectations. +Cliff clarified after this run that optimizer seed variation is not productive +routine allocator coverage: normalized post-Opto graphs should produce similar +backend work. Retain these historical reproductions, but use fixed-seed backend +validation going forward; seed variation belongs to optimizer investigations. +Stop for Cliff's review before starting Chapter 23. + ### Chapter 21 allocator: ready for review, 2026-09-20 Carries the Chapter 20 legality/progress/support fixes into 21 while retaining @@ -279,7 +479,7 @@ summarizes encoding/ELF, links the retained encoding reference, and ends with coalescing, both cohort rows, and the controlled comparison. Logs and isolated baseline/ablation sources are under `chapter21/build/regalloc-review` (ignored). The allocator changes remain confined to Chapter 21; the subsequent return/emulator -correction is recorded separately above. Chapter 22 allocator work awaits review. +correction is recorded separately above. Chapter 22 allocator work is recorded below the review heading. ### Chapter 20 allocator: ready for review, 2026-09-20 |