fix(codegen): the Float64Array region guard reads the receiver's storage byte

[proggeramlug]

Symptom

Compiling OpenCode v1.18.30 on main (Linux x86_64) fails four modules in codegen, all with the same LLVM IR parse error:

error: use of undefined value '@PERRY_TA_VIEW_GUARD'
  %r96 = load i64, ptr @PERRY_TA_VIEW_GUARD

The modules: packages/opencode/src/id/id.ts, @jridgewell/resolve-uri's UMD bundle, and two @smithy CJS bundles. The build then aborts with "4 module(s) failed to compile".

Cause

Two changes crossed on main:

• perf: one ArrayBuffer-aliasing view anywhere, even a dead one, makes all typed-array access 81× slower than Node (process-global PERRY_TA_VIEW_GUARD) #10516 (748cefbb7f, "the header says where elements live, not a global view count") removed the process-wide PERRY_TA_VIEW_GUARD — its runtime definition and its runtime_decls declaration. Every reader was switched to the receiver's own storage byte: header byte 10, TA_STORAGE_INLINE = 0.
• perf: the loop-hoisting tiers only admit single-statement, call-free bodies — a 6x store-path win produces 0.000% on real programs #10741 (63d69c9639) added emit_typed_f64_region_guard, the Float64Array twin of the dense-array region guard, and it still loads @PERRY_TA_VIEW_GUARD. It merged after perf: one ArrayBuffer-aliasing view anywhere, even a dead one, makes all typed-array access 81× slower than Node (process-global PERRY_TA_VIEW_GUARD) #10516, so it references a symbol that no longer exists anywhere.

It is not limited to Float64Array code. Any counted loop whose receiver is not declared a plain Array takes this guard, so a plain Buffer triggers it — id.ts has no typed array at all, only Buffer.alloc(6) and randomBytes(n) in two for loops. At run time such a receiver fails the guard's kind check and takes the slow path, but the IR still names the missing global, so the module never compiles.

Re-declaring the global would be wrong: the runtime no longer defines it, and a stub of 0 would tell the guard that every typed array uses inline storage, including views, whose elements are not at header + 16.

Fix

Read the receiver's storage byte, exactly as the other #10516 sites do (inline_dyn_typed_array.rs, property_get.rs): load i8 at header + 10, inline storage when it is 0. The offset is the runtime's #[repr(C)] TypedArrayHeader layout (length@0, capacity@4, kind@8, elem_size@9, storage@10), which that struct documents as part of the codegen contract.

Test

The existing #10741 test, a_float64array_receiver_reads_canonicalise_nan, generates exactly this guard but asserts only on IR text, so it could not see a reference to an undeclared symbol. The new a_typed_region_guard_names_only_symbols_that_exist builds the region loop for a Float64Array and for a Buffer receiver. It first asserts that the loop really takes the typed guard (rloop.ta), so it cannot pass vacuously; then it asserts that the guard does not name the removed global; then it runs the module through LLVM (testing::verify_ir).

• With the fix: passes.
• With guarded_array.rs reverted: fails at the global assertion, with the precondition holding.
• With guarded_array.rs reverted and the text assertion removed: the LLVM check alone fails with the production error, use of undefined value '@PERRY_TA_VIEW_GUARD'. So the verifier covers the whole class — any symbol the generated code names but nothing defines — not just this one name.

cargo fmt --all -- --check is clean. This is independent of #11817; together the two take the OpenCode build through codegen. The changelog fragment follows once this PR has a number.

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Reviewing files that changed from the base of the PR and between 0ed699b and 26f865f.

📒 Files selected for processing (2)

• crates/perry-codegen/src/expr/index_get/guarded_array.rs
• crates/perry-codegen/src/expr/region_array_loop_tests.rs

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