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

[Daniel Chen via flang-commits]

DanielCChen wrote:

As for the unaligned COMMON block variables, Fortran standard doesn't have an explicit rule to enforce it either way, so it is processor-dependent.

Each vendor, however, has quite different default behavior in terms of alignment rules for COMMON block variables.

- `gfortran`: enforce alignment by default, and has option`-fno-align-commons` to turn it off.
- `ifx/ifort`: no alignment by default,  and has`-align (no)commons, -align (no)dcommons` to enable or disable it.
- `IBM XLF`: no alignment by default, and has no option to toggle it.
- `flang`: seems inconsistent before the fix of this PR. I will break it down in in response to each test scenario.

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