https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70124
Bug ID: 70124
Summary: alignas error in constexpr function
Product: gcc
Version: 6.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: msebor at gcc dot gnu.org
Target Milestone: ---
Both attribute aligned and the alignas specifier are rejected with an error in
a constexpr function complaining that the alignment isn't a constant
expression. Attribute vector_size, on the other hand, is accepted in the same
context.
Note also that the diagnostic doesn't mention the value of the (constant)
argument or include the call site, making it difficult to determine which
invocation of the function caused the error when there is more than one.
$ cat x.c && /build/gcc-trunk-bootstrap/gcc/xg++ -B
/build/gcc-trunk-bootstrap/gcc -S -Wall -Wextra -Wpedantic -o/dev/null -xc++
x.c
constexpr int foo (unsigned N)
{
typedef __attribute__ ((aligned (1 << N))) int I;
I i = 0;
return i;
}
int i = foo (__alignof__ (int));
x.c: In function ‘constexpr int foo(unsigned int)’:
x.c:3:50: error: requested alignment is not an integer constant
typedef __attribute__ ((aligned (1 << N))) int I;
^
$ cat x.c && /build/gcc-trunk-bootstrap/gcc/xg++ -B
/build/gcc-trunk-bootstrap/gcc -S -Wall -Wextra -Wpedantic -o/dev/null -xc++
x.c
constexpr int foo (unsigned N)
{
alignas (1 << N) int i = 0;
return i;
}
int i = foo (__alignof__ (int));
x.c: In function ‘constexpr int foo(unsigned int)’:
x.c:3:17: error: ‘N’ is not a constant expression
alignas (1 << N) int i = 0;
^
x.c:3:17: error: ‘N’ is not a constant expression
