[all-commits] [llvm/llvm-project] aecfaf: [flang][acc] Handle fir.undefined with OutlineRema...

[khaki3 via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: aecfaf11953fe6117a15a26b81d86bb75813e09b
      https://github.com/llvm/llvm-project/commit/aecfaf11953fe6117a15a26b81d86bb75813e09b
  Author: khaki3 <47756807+khaki3 at users.noreply.github.com>
  Date:   2026-03-24 (Tue, 24 Mar 2026)

  Changed paths:
    M flang/lib/Optimizer/OpenACC/Support/RegisterOpenACCExtensions.cpp
    M flang/test/Fir/OpenACC/offload-livein-value-canonicalization.fir

  Log Message:
  -----------
  [flang][acc] Handle fir.undefined with OutlineRematerializationOpInterface in OffloadLiveInValueCanonicalization (#188325)

Example:
```fortran
!$ACC KERNELS PRESENT(CG, W1)
  CG(1:W1%WDES1%NPL, NN) = W1%CPTWFP(1:W1%WDES1%NPL)
  CPROJ(:, NN) = W1%CPROJ(1:SIZE(CPROJ,1))
!$ACC END KERNELS
```

When compiling OpenACC kernels containing array section assignments of
rank-2 arrays with a scalar index in one dimension (e.g. `CG(1:NPL,
NN)`), the Fortran lowering creates a `fir.slice` where collapsed
(scalar) dimensions use `fir.undefined index` as the stop/step values.
`SliceOp::getOutputRank()` relies on `getDefiningOp()` returning
`fir::UndefOp` to identify these collapsed dimensions and compute the
correct output rank.

When `fir.undefined` values defined outside an offload region are used
inside it, `gpu-kernel-outlining` turns them into function arguments.
Since function arguments have no defining op (`getDefiningOp()` returns
`nullptr`), `getOutputRank()` no longer recognizes the collapsed
dimensions, computing rank 2 instead of rank 1. This causes the
`fir.rebox` verifier to fail with:

```
'fir.rebox' op result type rank and rank after applying slice operand must match
```

Fix: Register `OutlineRematerializationOpInterface` for `fir::UndefOp`
(and `fir::SliceOp`) in `RegisterOpenACCExtensions.cpp`. This causes
`OffloadLiveInValueCanonicalization` to clone these operations inside
the offload region before outlining, preserving the `fir::UndefOp`
identity so that `getOutputRank()` correctly identifies collapsed
dimensions.



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