[PTOAS] finalize pipe init nosplit semantics

[TaoTao-real]

Summary

• add explicit frontend nosplit support for aic/aiv_initialize_pipe
• infer missing internal init nosplit from downstream split usage for backward compatibility
• validate mixed split usage / explicit-nosplit conflicts before memory planning
• align A3/A5 EmitC TPipe template argument order with the updated pto-isa layout

Motivation

• follow up on PR infer pipe init nosplit from split-0 users #452 without burying more semantics in ResolveReservedBuffers
• preserve compatibility for older IR such as test/samples/TPushTPop/test3/kernel.pto that omits init-level nosplit
• let newer IR spell nosplit explicitly and fail early when user intent conflicts with downstream split

Design

• frontend ops now accept optional nosplit and forward it during pto-lower-frontend-pipe-ops
• new pto-infer-validate-pipe-init module pass runs before memory planning to:
  • infer nosplit=true/false from tpush/tpop/tfree split usage when missing
  • reject split=0 mixed with split=1/2 on the same logical pipe
  • reject explicit nosplit mismatches and peer-pipe conflicts
  • propagate the resolved nosplit across peer init pairs
• pto-resolve-reserved-buffers is narrowed back to flag-base alignment + reserve/import address materialization
• EmitC now emits:
  • A3/A2: TPipe<flag, dir, slotSize, slotNum, nosplit, localSlotNum>
  • A5: TPipe<flag, dir, slotSize, slotNum, nosplit>

Testing

• build: ninja -C build ptoas
• targeted regressions:
  • test/basic/tpush_tpop_emitc.pto
  • test/basic/tpush_tpop_frontend_lowering_a3.pto
  • test/basic/tpush_tpop_frontend_lowering_a5.pto
  • test/basic/tpush_tpop_frontend_nosplit_a5.pto
  • test/basic/tpush_tpop_frontend_mixed_split_a5.pto
  • test/basic/tpush_tpop_frontend_nosplit_conflict_a5.pto
  • test/basic/resolve_reserved_buffers_reject_incomplete_peer_group_a5.pto
  • test/basic/resolve_reserved_buffers_reject_non_peer_init_a5.pto
• sample compatibility:
  • ptoas --pto-arch=a5 --enable-insert-sync test/samples/TPushTPop/test3/kernel.pto
  • verified generated C++ still contains TPipe<0, Direction::DIR_BOTH, 1024, 4, true> plus matching TPUSH/TPOP/TFREE for the round-trip path

Risk / Rollback

• risk: stacked on top of PR infer pipe init nosplit from split-0 users #452 (codex/pipe-init-nosplit), so merge order matters
• rollback: revert this PR to restore PR452 behavior while keeping the base branch intact

[gemini-code-assist]

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