https://bugs.llvm.org/show_bug.cgi?id=48740
Bug ID: 48740
Summary: OpenMP declare reduction in C does not require an
initializer
Product: OpenMP
Version: unspecified
Hardware: PC
OS: Linux
Status: NEW
Severity: enhancement
Priority: P
Component: Clang Compiler Support
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected]
The following C snippet:
// t.c
struct S {
int x;
};
#pragma omp declare reduction(udr_int : int : omp_out)
#pragma omp declare reduction(udr_agg : struct S : omp_out)
int main() {
int x = 0;
struct S s = {};
#pragma omp parallel reduction(udr_int : x)
{ }
#pragma omp parallel reduction(udr_agg : s)
{ }
}
// end of t.c
When compiled using
clang -c t.c -fopenmp
emits the following diagnostic
t.c:12:42: error: list item of type 'int' is not valid for specified
reduction operation: unable to provide default initialization value
#pragma omp parallel reduction(udr_int : x)
~~~~~~~ ^
t.c:10:7: note: 'x' defined here
int x = 0;
^
t.c:14:42: error: list item of type 'struct S' is not valid for specified
reduction operation: unable to provide default initialization value
#pragma omp parallel reduction(udr_agg : s)
~~~~~~~ ^
t.c:11:12: note: 's' defined here
struct S s = {};
^
2 errors generated.
but my reading of the OpenMP spec suggests that this is actually not required
for C[1]
(C) If no initializer-clause is specified, the private variables will be
initialized following the rules for initialization of objects with static
storage duration.
GCC accepts this code.
This issue can be worked around using an `initializer` clause such as
`initializer(omp_priv = {})` for `udr_agg`.
[1] https://www.openmp.org/spec-html/5.1/openmpsu117.html
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