https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87911
Bug ID: 87911
Summary: OpenACC/OpenMP clauses parsing: comma operator vs.
separator
Product: gcc
Version: 9.0
Status: UNCONFIRMED
Keywords: openacc, openmp
Severity: minor
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: tschwinge at gcc dot gnu.org
CC: jakub at gcc dot gnu.org
Target Milestone: ---
All over OpenACC/OpenMP clauses parsing we sometimes diagnose "warning: left
operand of comma operator has no effect" (C) or "warning: left-hand operand of
comma expression has no effect" (C++) vs. "error: expected ')' before ','
token". For example:
void f()
{
#pragma omp parallel num_threads (3, 4)
;
#pragma omp target device (5, 6)
;
}
C:
../oo.c: In function 'f':
../oo.c:3:36: warning: left-hand operand of comma expression has no effect
[-Wunused-value]
3 | #pragma omp parallel num_threads (3, 4)
| ^
../oo.c:6:29: error: expected ')' before ',' token
6 | #pragma omp target device (5, 6)
| ~ ^
| )
C++:
../oo.c: In function 'void f()':
../oo.c:3:38: warning: left operand of comma operator has no effect
[-Wunused-value]
3 | #pragma omp parallel num_threads (3, 4)
| ^
../oo.c:6:31: warning: left operand of comma operator has no effect
[-Wunused-value]
6 | #pragma omp target device (5, 6)
| ^
I see how this is happening in the front ends.
Note that at least for OpenACC there are certain clauses that do need the comma
as separator, for they accept several expressions: "wait (1, 2, 3)", for
example. Is there any good reason that the single-argument clauses should use
the comma operator semantics (consistently)? I have not verified the
OpenACC/OpenMP standards, but I suppose user expectation would be to diagnose
all these as syntax errors? (Jakub?)
(Also note how the caret location is different for C and C++, and not quite
right for both. But that seems to be a general problem, also seen for "return
1, 2;", for example.)
