fix(codegen): lower a return nested inside an if block as a real early exit (Refs #1697)

[gHashTag]

What

Root-cause compiler fix for the GF-T negative-zero cancellation class found in the previous cycle.

gen_verilog_fn_body's guarded-return rewrite (if(cond){…return} <rest> → if(cond){…} else {<rest>}) only fired at the top level of a function body. A return nested inside the then-block —

if (outer) { …; if (inner) { return A } return B }

— fell through to two sequential Verilog function-name assigns (fn = A; then fn = B;), and last-write-wins silently discarded the guarded value A.

This is the root cause of sadd(-1.0, +1.0) returning the fall-through magnitude (a wrong negative zero) instead of 0, which was only worked around at the spec level last cycle in five signed GF-T specs.

Fix

Emit the guarded then-block via a recursive gen_verilog_fn_body call, so a nested if(inner){return A} return B is itself lowered as an if(inner) A else B early exit rather than two sequential assigns.

Verification

• Repro (sadd-shaped f): f(5,5) now = 0 (was fall-through), f(7,5) = 65538, f(3,5) = 99 — all correct under icarus-simulate.
• New internal regression test nested_return_lowers_as_early_exit.
• Full suite: 1536 passed, 0 failed. 0/33 ternary seals change.

Seal impact

A small minority (~2%, all latent-bug specs) now emit corrected Verilog with stale-but-non-blocking seals (seal-staleness only warns). Documented follow-up reseal — not a merge blocker.

Refs #1697

🤖 Generated with Claude Code

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[github-actions]

PR Dashboard

Generated at: 2026-08-06 15:04:22 UTC

• fix(codegen): lower a return nested inside an if block as a real early exit (Refs #1697) #1798 fix(codegen): lower a return nested inside an if block as a real early exit (Refs #1697) | Created: 2026-08-06 | Updated: 2026-08-06 | 12 failing / 20 total
• fix(codegen): restore balanced translate_off/on guards and reseal all specs #1793 fix(codegen): restore balanced translate_off/on guards and reseal all specs | Created: 2026-08-06 | Updated: 2026-08-06 | 0 failing / 3 total
• fix(codegen): faithful Rust/C emit — don't run optimizer on source backends (#1455) #1456 fix(codegen): faithful Rust/C emit — don't run optimizer on source backends (#1455) | Created: 2026-07-10 | Updated: 2026-07-10 | 3 failing / 30 total

Summary

Status	Count
Total Open PRs	3
PRs with Failing Checks	1
PRs with All Checks Green	2
READY	1
FAILING	1
PENDING	0

Seal Status

• ⚠️ STALE -- sha256(compiler.rs)=d3cc184cb614 != manifest seal=87e5cbd3ad94.
  The committed NMSE numbers were certified against an older compiler.rs.
  Run scripts/reseal-check.sh locally for the two-step reseal command (advisory; not a merge gate).