[all-commits] [llvm/llvm-project] 7d1a8f: [flang] Fix FIR AliasAnalysis for zero-offset view...

[khaki3 via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 7d1a8f197c57ee2d36c18a2920344f34111394b8
      https://github.com/llvm/llvm-project/commit/7d1a8f197c57ee2d36c18a2920344f34111394b8
  Author: khaki3 <47756807+khaki3 at users.noreply.github.com>
  Date:   2026-05-05 (Tue, 05 May 2026)

  Changed paths:
    M flang/lib/Optimizer/Analysis/AliasAnalysis.cpp
    M flang/test/Analysis/AliasAnalysis/alias-analysis-pack-array.fir
    A flang/test/Analysis/AliasAnalysis/alias-analysis-zero-offset-view-chain.fir
    M flang/test/Transforms/OpenACC/acc-implicit-data.fir

  Log Message:
  -----------
  [flang] Fix FIR AliasAnalysis for zero-offset view chains (#192710)

When subroutine `f` below is inlined, the `ACCImplicitData` pass fails
to recognize that `b` is already covered by the enclosing `!$acc data
deviceptr`. The deviceptr clause operates on a box (`fir.embox` result)
while the inner `acc.serial` uses the underlying ref.
`fir::AliasAnalysis` traces both back through the full def-chain, where
an upstream sliced `fir.embox` (from `a(:,5)`) sets
`approximateSource=true`, causing `MayAlias` instead of `MustAlias`. The
pass falls back to implicit `copyin`/`copyout`, causing a segfault.

```fortran
module test_mod
  real, allocatable :: a(:,:)
contains
  subroutine f(b)
    real, dimension(*) :: b
    !$acc data deviceptr(b(1:100))
    !$acc serial
    print *, b(10)
    !$acc end serial
    !$acc end data
  end subroutine f
end module test_mod

program test
  use test_mod
  call alloc_a
  !$acc data present(a)
  !$acc host_data use_device(a)
  call f( a(:,5) )
  !$acc end host_data
  !$acc end data
end program
```

Fix: add `getZeroOffsetViewRoot()` as a short-circuit in `alias(Source,
Source, Value, Value)`. Before consulting `approximateSource`, it walks
each value backward through `FortranObjectViewOpInterface` ops with zero
offset (embox without slice, declare, box_addr) to find its root. If
both values share the same root, `MustAlias` is returned immediately,
avoiding the conservative `MayAlias` caused by distant
`approximateSource` flags.



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