[flang] Change C889 from error into warning

[peixin]

Summary

This constraint is used in OMP2012 benchmark, and other compilers do not
enforce it. Change it into one warning. This addresses the issue
https://github.com/llvm/llvm-project/issues/56003.

[kiranchandramohan]

LGTM. This will help make progress with SpecOMP testing for the OpenMP team. Also, other compilers do not enforce it and gfortran gives a warning.

You can submit it after a day if there are no further requests for changes.

[peixin]

In D127740#3581409, @kiranchandramohan wrote:

LGTM. This will help make progress with SpecOMP testing for the OpenMP team. Also, other compilers do not enforce it and gfortran gives a warning.

You can submit it after a day if there are no further requests for changes.

OK. Thanks.

[klausler]

If no other compiler enforces this useless constraint, then there is no portability concern.

[peixin]

Considering gfortran has warnings, change the portability warning into warning.

[peixin]

Use _warn_en_US.

flang/lib/Semantics/resolve-names.cpp

 void DeclarationVisitor::CheckSaveStmts() {
   for (const SourceName &name : specPartState_.saveInfo.entities) {
     auto *symbol{FindInScope(name)};
     if (!symbol) {
       // error was reported
     } else if (specPartState_.saveInfo.saveAll) {
       // C889 - note that pgi, ifort, xlf do not enforce this constraint
       Say2(name,
-          "Explicit SAVE of '%s' is redundant due to global SAVE statement"_err_en_US,
+          "Explicit SAVE of '%s' is redundant due to global SAVE statement"_warn_en_US,
           *specPartState_.saveInfo.saveAll, "Global SAVE statement"_en_US);
     } else if (auto msg{CheckSaveAttr(*symbol)}) {
       Say(name, std::move(*msg));
       context().SetError(*symbol);
     } else {
       SetSaveAttr(*symbol);
     }
   }

flang/test/Semantics/resolve45.f90

 subroutine s3(x)
   !ERROR: SAVE attribute may not be applied to dummy argument 'x'
   procedure(integer), pointer, save :: x
   !ERROR: Procedure 'y' with SAVE attribute must also have POINTER attribute
   procedure(integer), save :: y
 end
 
 subroutine s4
-  !ERROR: Explicit SAVE of 'z' is redundant due to global SAVE statement
+  !WARNING: Explicit SAVE of 'z' is redundant due to global SAVE statement
   save z
   save
   procedure(integer), pointer :: x
-  !ERROR: Explicit SAVE of 'x' is redundant due to global SAVE statement
+  !WARNING: Explicit SAVE of 'x' is redundant due to global SAVE statement
   save :: x
-  !ERROR: Explicit SAVE of 'y' is redundant due to global SAVE statement
+  !WARNING: Explicit SAVE of 'y' is redundant due to global SAVE statement
   integer, save :: y
 end
 
 subroutine s5
   implicit none
   integer x
   block
     !ERROR: No explicit type declared for 'x'