MechaCat02 9ab986ec09 fix(cpu): SWAPBUG-001 — revert addi 32-bit truncation ...

The addi opcode was truncating its result to 32 bits per the post-P4-batch3
"32-bit ABI" rationale (commit bf8208e). Hunk-level bisection during the
2026-05 audit (M11) isolated this single cast as the cause of the
post-P8 swap regression: swaps dropped 2 → 1 and the renderer lost a
frame. PowerISA mandates sign-extension to 64 bits; canary does not
truncate addi. The truncation was a canary-divergent over-extension
of the addis fix (which IS canary-divergent by design, see
addis at interpreter.rs:121-134).

The addi_li_neg_one_zero_extends_upper test encoded the wrong invariant.
Replaced with a sign-extension test asserting canonical PowerISA
behavior (gpr[3] == 0xFFFF_FFFF_FFFF_FFFF for `li r3, -1`).

Verification at -n 100M lockstep:
  swaps:                1 → 2     (gate met)
  draws:                0 → 0     (unchanged — gated by Phase C+D+E)
  instructions:         ~100M (unchanged)
  imports:              11.4M → 987k    (game escapes retry loop)
  packets:              281M → 57M      (same)
  interrupts_delivered: 629 → 630
Tests: 551 passing (unchanged). Lockstep determinism: byte-identical
across two 100M runs except packets (±5%, GPU-thread-race noise floor).

Closes SWAPBUG-001 / PPCBUG-001.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

2026-05-03 13:37:51 +02:00

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