[flang-commits] [flang] [flang] Fix incorrect offset for zero-size COMMON block members. (PR #214174)

[Daniel Chen via flang-commits]

DanielCChen wrote:

> Another test to check:
> 
> ```
> program p20
>   character(1) :: c1
>   real(8) :: z0(0)
>   character(1) :: c2
>   common /blk/ c1, z0, c2
>   print '(A,I0,1X,I0)', 'p20 z0,c2: ', loc(z0) - loc(c1), loc(c2) - loc(c1)
> end program
> ```

For `p20`, flang outputs `0 1` before the fix and `1 1` with the fix in the PR. It seems reasonable in the scope of this PR in the sense that no alignment for the zero-sized variable and natural alignment for `character(1)` variables.

**Ref outputs (all by default):**

- gfortran: `8 8`
- ifx/ifort: `1 1` (it outputs 4 4 or 8 8 if -align commons or -align dcommons option is used.)
- IBM XLF: `1 1`

https://github.com/llvm/llvm-project/pull/214174