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feat(codegen): recursive reassignment + read scan in optimizer passes - #1465
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Three surgical fixes to the optimizer that together let mut-inference (PR #1461) actually deliver clean gen/rust on downstream repos: 1. const_propagate: reassigned-check now uses collect_mutable_names, which already recurses into if/while/for/for-range bodies. Previously a `let X = <literal>` reassigned INSIDE a control-flow block was incorrectly considered non-reassigned, inlined, and its declaration dropped, leaving dangling `X = ...` reassignments in emit. 2. copy_propagate: same recursive reassigned-check guard added. A `let X = Y` where X is reassigned later (including inside control-flow) is no longer copy-propagated. 3. dead_store_elim: new helper collect_reads_in_stmts recurses into if/while/for/for-range bodies when building the `reads` set. Without this a `let i = 0;` that is only read inside a `while` body was seen as dead and eliminated. StmtAssign with a simple-identifier LHS still contributes only the RHS to `reads` (pre-existing dead-store semantics preserved). Measured on tri-net specs (all 119 regenerated): - baseline PR #1461 (SHA 6171697): cargo check --lib -> 208 errors (145x E0425 cannot-find-value, 26x E0107 Vec generics, misc) - this PR: cargo check --lib -> 28 errors (26x E0107 Vec generics, 2x independent) - delta: -180 errors, -87%. E0425 -> 0. t27c own tests: 1491 passed / 3 failed. Same 3 pre-existing failures (#1401 let_binding_is_lowered / test_let_binding_emitted_{c,rust}_1401) that already fail on baseline 6171697; not a regression from this PR. FROZEN_HASH re-sealed via bootstrap/stage0 ceremony. Remaining 28 errors are independent bugs (Vec<> generics elision and 2 type-inference edge cases), not touched by this PR. phi^2 + phi^-2 = 3
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What
Three optimizer passes (
const_propagate,copy_propagate,dead_store_elim) checked for reassignment/reads only at the top-level statement list, without recursing into if/while/for bodies. Locals reassigned inside conditionals had theirletdropped or identifiers inlined, leaving dangling references (E0425).Fixes #1464
How
Recursive reassignment and read scanning in all three passes:
const_propagate: usesassigns_to_recursive()instead of top-level scancopy_propagate: same recursive check before inliningdead_store_elim:collect_reads_in_stmts()recurses into control-flow bodiesassigns_to_recursive(): mirrorscollect_mutable_namespatternMeasured impact (tri-net, cross-env verified)
Cross-env verified: 28 errors on linux, 26 on macOS arm64.
Files
bootstrap/src/compiler.rs— +50 lines (3 pass fixes + helper function)Supersedes closed #1462 (base branch deleted by squash merge of #1461).
phi^2 + phi^-2 = 3