[PATCH] D119373: [flang] Make folding of LEN less aggressive

[Jean Perier via Phabricator via llvm-commits]

jeanPerier added a comment.

> IsConstantExpr() is too strict of a test; IsScopeInvariantExpr() would be better.

@klausler, while I agree `IsConstantExpr` is throwing away valid rewrites, `IsScopeInvariantExpr` is still letting invalid rewrites like the following:

  module m
  contains
    function cfoo(l)
      integer :: l
      character(l) :: cfoo
      cfoo = "hello"
    end function
  
    subroutine bug(n)
      integer :: n
      print*, len(cfoo(n))
    end subroutine
  end module

`flang-new -fc1 -fdebug-unparse %` rewrites  `print*, len(cfoo(n))`  in `bug` into `PRINT *, int(cfoo%len,kind=4)`, that looks wrong to me. And if the `l` dummy argument is made `intent(in)` in `cfoo`, then `print*, len(cfoo(n))` is rewritten to `PRINT *, int(max(0_8,int(l,kind=8)),kind=4)`, which is also wrong. The information about the actual argument that defines the length was lost and cannot be retrieved anymore.

So a deeper analysis needs to be done here to avoid using `IsConstantExpr`, or LEN() should be changed.


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D119373/new/

https://reviews.llvm.org/D119373