test(optimizer-bridge): delegate count_arm_byte_size to the production estimator (#511 follow-on, #242)

[avrabe]

What

A small test consolidation following #511. The #[cfg(test)] byte-counting helper count_arm_byte_size was a hand-maintained mirror of the optimized-path size table — a drifted copy with its own _ => 4 default and only a partial op set (a "mirror of a mirror").

#511 extracted that table to estimate_arm_byte_size and established the real independent check — the estimator_encoder_agreement oracle, which pins the table against the actual Thumb-2 encoder (the ground truth). With the encoder as the independent oracle, the local hand-drifted proxy is redundant.

How

• Replace the helper body with arm.iter().map(estimate_arm_byte_size).sum().
• Delete the now-unused reg_idx test helper. −43 lines.

Why it's safe (test-only, production codegen untouched)

estimate_arm_byte_size is unchanged — only the test helper's body is replaced, so this is frozen-by-construction (the frozen byte gate is vacuous here, as in #511).

The three test_issue94_* consumers assert bytes < 30 on post-optimization sequences (Mov/Movw/Asr — all ≤ 4 bytes in both the old proxy and the production table) plus direct structural checks (!has_runtime_shift, asr_count == 1). The production estimator's _ => 2 default yields counts ≤ the old proxy's _ => 4, and the explicitly-sized ops match exactly, so every assertion still holds.

Verification: whole synth-synthesis suite green (463 lib tests); no unused-symbol warnings (confirms reg_idx had no other consumer); fmt + clippy clean.

Scope

Test consolidation — a #511 follow-on. Not a codegen change, not a #242 north-star advance. Refs #511, #242.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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