[aasul]

AI assistance disclosure: OpenAI Codex assisted with development, source review, validation, and this description.

Preserve identical typed constants when assignment cleanup paths produce the same IR constant. Building a PHI and then a CV-bound COPY can let the constant spill move before the guard protecting the assignment and overwrite a still-live CV value.

Separately, give reusable pure-expression results and CV assignments distinct hard COPY identities. A later assignment can otherwise overwrite a CV-backed spill that CSE still needs. After optimized liveness and coalescing, reuse the checked assignment COPY's storage only for adjacent, identically typed definitions whose ranges cover every later source range. Reject coalesced/live-in intervals and direct source snapshots, and retain independent storage when those checks fail.

The extra independent values initially exhausted the fixed trace spill frame on a five-expression floating-point workload: the earlier A+C candidate compiled one trace and logged 26 compilation errors. Checked sharing restores two compiled traces with zero errors; read-only probes on current PHP 8.4 and 8.5 show 16 bytes needed within the unchanged 32-byte frame.

Regression coverage includes the original A case, the original two-file C case, a natural floating-point CSE failure, and a pressure test that requires successful trace compilation without requiring an exact trace count. The floating-point PHPT naturally reports wrong: 725 before C's correction and wrong: 0 afterward on local x86_64.

Final Linux x86_64 validation (zero failures or warnings in these runs):

Configuration	PASS	SKIP
Current PHP 8.4 debug NTS, full JIT directory (59f8e1d2653c)	505	10
Current PHP 8.5 debug NTS, full JIT directory (2546fe9e827e)	520	10
Current PHP 8.4 + #24484 and #24635, full JIT directory	508	10
Preserved PHP 8.5 + both PRs, full JIT directory (d98dc49a9a59)	522	10
PHP 8.5 debug ZTS, full JIT directory (d98dc49a9a59)	519	10
PHP 8.5 release NTS, four new PHPTs (d98dc49a9a59)	4	0
Committed PHP 8.4 files, final focused PHPT run	4	0

Nine fixtures agree across interpreter, function JIT, and tracing JIT in each of those six runtime configurations. Original A compiles its loop and caller link (six traces), original C compiles its root (one trace), and the floating-point and unchanged pressure workloads each compile two traces, all without compilation errors.

The original C reproduction already passes naturally on local x86_64 builds before this change. The separate floating-point reproducer and the earlier controlled spill-store diagnostic provide additional evidence: the diagnostic produced 939 wrong calls before / zero after on PHP 8.5, and 936 / zero on PHP 8.4. Those diagnostic artifacts were reviewed separately from natural execution. Natural ARM64 validation remains outstanding.

Compatibility was checked with the actual code and tests at #24484 head 53f79bd859dd5a0c7e2dbfea363dec760512e6b8 and #24635 head 54b5f7cf0c5e2796d62ecaf0c280d0c7e53be1e7. The conflict check still runs before the new COPY, preserving #24484's older-reference safeguard. Both GH-24471 tests pass standalone, but that behavioral overlap does not replace #24484. GH-24634 still requires #24635: its separate test fails standalone and passes in both combined builds.

This contribution covers the two inspected mechanisms, not every possible CV binding problem. Reproduction B still cannot compile its intended tracing path locally (zero compiled traces, 14 compilation errors) and remains unresolved; correct fallback output is not evidence of a B fix.

Refs GH-24683.

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