[AIE] Fix instruction-select crash on unpack of a non-load value

[hunhoffe]

Note: I'm just a peano user, not a dev -- agents helped copiously in this PR, so I'd appreciate a thorough review.

Problem

Feeding the result of acc.to_vector<int8>() directly into aie::unpack crashes Peano with a SIGSEGV during instruction selection, on both AIE2 and AIE2P.

Minimal C++ reproducer (clang++ --target=aie2p-none-unknown-elf -O2):

  #include <aie_api/aie.hpp>
  aie::vector<int16, 32> bad(aie::vector<int8, 32> a, aie::vector<int8, 64> b) {
    using MMUL = aie::mmul<4, 8, 8, int8, int8>;
    MMUL acc; acc.mac(a, b);
    aie::vector<int8, 32> proj = acc.to_vector<int8>(8);
    return aie::unpack(proj);            // <- proj feeds unpack directly
  } 

Backtrace:

• AIE2PInstructionSelector::getCombinedOpcodeUNPACKLoad
• AIE2PInstructionSelector::canCombineUNPACKLoad
• AIEBaseInstructionSelector::selectG_AIE_LOAD_UNPACK
• llvm::InstructionSelect::selectMachineFunction

Root cause

selectG_AIE_LOAD_UNPACK tries to fold a load directly into the unpack. It gates the fold on MemOp.mayLoad(), then calls getLoadStoreSize(MemOp), which dereferences the instruction's first memory operand:

  return (*MI.memoperands_begin())->getSizeInBits().getValue();

The producer here is the SRS narrowing intrinsic (the lowering of to_vector<int8>()), a G_INTRINSIC_W_SIDE_EFFECTS that reports mayLoad() but carries no memory operand. memoperands_begin() == memoperands_end(), so the dereference reads an invalid pointer → segfault.

Fix

Bail out of the combine when the candidate has no memory operand, so a non-load producer falls back to normal VUNPACK selection. Applied to both the AIE2 and AIE2P selectors (both had the identical latent crash).

Testing

• New MIR regression tests for both targets (inst-select-unpack-non-load.mir); they SIGSEGV before this change and select cleanly after.
• Real load→unpack still folds into VLDB_UNPACK (existing inst-select-*vldb_unpack.mir tests unchanged).
• Full llvm/test/CodeGen/AIE/{aie2,aie2p}/GlobalIS*el suites pass locally (391/391).

[martien-de-jong]

Have you tried AIE2PS? If it doesn't occur there, it may mean that the memory operand modeling/handling is better there.

[hunhoffe]

@martien-de-jong Verified — AIE2P crashes identically before this fix. The guard logic in AIE2PInstructionSelector::getCombinedOpcodeUNPACKLoad was if (!MemOp.mayLoad()) return {}; with no memoperands_empty() check, so the same null-deref SIGSEGV occurs. I confirmed this by running the new inst-select-unpack-non-load.mir test against an unpatched build (exit 139 / SIGSEGV) and a patched build (exit 0, selects VUNPACK_mv_unpack_w_unpackSign1).