[all-commits] [llvm/llvm-project] afb584: [SelectionDAG] Ensure that we don't create `UCMP`/...

[Volodymyr Vasylkun via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: afb584a5622d67d19539d30287bc8af461f48ca8
      https://github.com/llvm/llvm-project/commit/afb584a5622d67d19539d30287bc8af461f48ca8
  Author: Volodymyr Vasylkun <vvmposeydon at gmail.com>
  Date:   2024-07-12 (Fri, 12 Jul 2024)

  Changed paths:
    M llvm/lib/CodeGen/SelectionDAG/LegalizeVectorTypes.cpp
    M llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
    M llvm/test/CodeGen/AArch64/ucmp.ll

  Log Message:
  -----------
  [SelectionDAG] Ensure that we don't create `UCMP`/`SCMP` nodes with operands being scalars and result being a 1-element vector during scalarization (#98687)

This patch fixes a problem that existed before where in some situations
a `UCMP`/`SCMP` node which operated on 1-element vectors had a legal
result type (i.e. `v1i64` on AArch64), but illegal operands (i.e.
`v1i65`). This meant that operand scalarization was performed on the
node and the operands were changed to a legal scalar type, but the
result wasn't. This then led to `UCMP`/`SCMP` nodes with different
vector-ness of operands and result appearing in the SDAG. This patch
addresses this issue by fully scalarizing the `UCMP`/`SCMP` node and
then turning its result back into a 1-element vector using a
`SCALAR_TO_VECTOR` node.

It also adds several assertions to `SelectionDAG::getNode()` to avoid
this or a similar issue arising in the future. I wasn't sure if these
two changes are unrelated enough to warrant two small separate PRs, but
I'm happy to split this PR into two if that's deemed more appropriate.



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