| Issue |
184927
|
| Summary |
[Flang][OpenMP] declare reduction on derived types fails: verifier error with initializer, abort without initializer
|
| Labels |
flang
|
| Assignees |
|
| Reporter |
nakazawa-fj
|
```
flang version 23.0.0git (https://github.com/llvm/llvm-project.git 3f024d08355d40e935d89c19d799ccdd298e95a7)
```
When using OpenMP `declare reduction` in LLVM Flang to define a user-defined reduction for a derived type,
compilation fails in both cases: with an initializer clause and without an initializer clause.
sample.f90
```fortran
implicit none
type t
integer::member
end type t
integer::i
!$omp declare reduction(a:t:omp_out%member=omp_out%member+omp_in%member)
!$omp initializer(omp_priv%member=0)
type(t)::x1
x1%member=0
call omp_set_num_threads(2)
!$omp parallel do reduction(a:x1)
do i=1,10
x1%member=x1%member+1
end do
!$omp end parallel do
print *,"pass"
end program
```
### Actual Result (with initializer)
```
$ flang sample.f90 -fopenmp
error: loc("/work/home/suguro/bug-report/15401/sample.f90":1:3): 'omp.declare_reduction' op expects initializer region to yield a value of the reduction type
error: verification of lowering to FIR failed
```
### Behavior without the initializer clause
If the initializer clause is removed:
```fortran
!$omp declare reduction(a:t:omp_out%member = omp_out%member + omp_in%member)
```
the compilation fails with the following error:
```
$ flang sample.f90 -fopenmp
error: loc("/work/home/suguro/bug-report/15401/sample.f90":1:3): /work/groups/ssoft/compiler/llvm/src/llvm-main/flang/lib/Lower/OpenMP/ClauseProcessor.cpp:471: not yet implemented: declare reduction without an initializer clause is not yet supported
LLVM ERROR: aborting
```
```
$ gfortran sample.f90 -fopenmp
sample.f90:6:26:
6 | !$omp declare reduction(a:t:omp_out%member=omp_out%member+omp_in%member)
| 1
Error: Missing INITIALIZER clause for !$OMP DECLARE REDUCTION of derived type without default initializer at (1)
```
```
$ ifx sample.f90 -fopenmp
$ ./a.out
pass
```
With an initializer clause, flang attempts to handle `declare reduction`, but fails at the FIR verification stage, leading to a verification error.
Without an initializer clause, flang emits a diagnostic indicating that the feature is not yet implemented.
According to OpenMP 6.0, Section 7.6.14, a declare_reduction is fully identified by the reduction identifier and type-name list,
so the initializer clause is optional. However, compiler behavior differs in practice: some compilers (e.g., gfortran)
impose additional constraints, while others (ifx) accept this code.
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