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diff --git a/skills/chapter25-codex-notes.md b/skills/chapter25-codex-notes.md index 0bb324ac..ea794c8b 100644 --- a/skills/chapter25-codex-notes.md +++ b/skills/chapter25-codex-notes.md @@ -50,6 +50,32 @@ lessons rather than duplicating that history. files. The B13 `chapter25/tmp` probes were removed at Cliff's request after he reviewed and pushed the fix; future sessions must not rely on those files. +## Dominator caches and searches + +- Real dominator searches start in Chapter 6 (If and Region), before CFGNode + appears in 11. Regions recompute their dominator from current predecessors + using the shared `domLCA` walk; do not cache a dominator pointer just because + the old node is still alive. Rewiring a merge can change its dominator. +- Chapters 6-17 cache a `char` depth with zero meaning unset. From 18, inlining + requires a separate `char` cache version and a checked global version bump. + Keep depth/version as separate fields rather than packing arithmetic into an + int. Assert before narrowing a depth or incrementing the version: 65535 is + the largest representable value, and wrapping must fail clearly. +- Copy both cache fields when copying a CFG node. Ordinary `Node.copy()` clones + already preserve them; CFG copy constructors must do so explicitly. Inlining + invalidates afterward, but future local CFG transforms may preserve valid + caches outside their edit region. +- Every cached depth override, including Region, Loop and Stop, participates in + version validation. Start has fixed depth zero; an unfolded function is a + root, while a folding function uses its new caller-side depth. Preserve the + chapter's dependency direction and dead-predecessor rules when sharing walks. +- Cliff requested removing the dedicated dominator bookkeeping tests/helpers; + do not restore them without a substantive failure to cover. Keep existing + printer cache snapshots checking both fields; cast char depths to int for + numeric display. +- Keep single-return accessors and overrides compact on one line, including + `idepth()` and `validIDepth()`. + ## Null guards: B13 / issue #246 lessons - Null refinement starts in Chapter 10; arrays in 15; scoped expression guards @@ -178,6 +204,12 @@ Consequences: ## Functions and escape analysis +- Unified function returns start in Chapter 18. Check return compatibility from + the optimized return expression, not a parse-time meet that includes dead + exits. Parse-time type-kind flags may describe an error, but must not decide + whether an error exists. Earlier snapshots keep separate Return nodes; they + already accept dead mixed-type exits and do not enforce one common return type. + - A constant Simple function address must be a `FunPtrNode`, not an ordinary `ConstantNode`, so the pointer retains an edge to the function Return. - Before Opto, a live FunPtr keeps its function callable even if no Call is |