[flang-commits] [flang] [flang][OpenACC] Relax COMMON block usage restriction in OpenACC directives (PR #162659)

[Eugene Epshteyn via flang-commits]

================
@@ -3627,6 +3627,27 @@ void ModuleVisitor::Post(const parser::UseStmt &x) {
       }
     }
   }
+  // Go through the list of COMMON block symbols in the module scope and add
----------------
eugeneepshteyn wrote:

COMMON block names and sizes are already stored in `SemanticsContext`, available via `SemanticsContext::GetCommonBlocks()`. This is what lowering is using to generate correctly sized blob for COMMON.

We already have a warning for COMMON size differences. The following code
```
module common_multi_mod_a
  integer :: a
  common /my_common/ a
end module

module common_multi_mod_b
  integer :: b
  integer :: c
  common /my_common/ b, c
end module

subroutine s1()
  use common_multi_mod_a
  a = 1
end subroutine

subroutine s2()
  use common_multi_mod_b
  b = 2
  c = 3
end subroutine

subroutine s3()
  use common_multi_mod_b
  use common_multi_mod_a
  a = 4
  b = 5
  c = 6
end subroutine
```
... generates the following warning:
```
$ flang -c common-multi-mod.f90 -pedantic
./common-multi-mod.f90:9:11: portability: A named COMMON block should have the same size everywhere it appears (8 bytes here) [-Wdistinct-common-sizes]
    common /my_common/ b, c
            ^^^^^^^^^
./common-multi-mod.f90:3:11: Previously defined with a size of 4 bytes
    common /my_common/ a
            ^^^^^^^^^
```

https://github.com/llvm/llvm-project/pull/162659